Wireless Setup

Third-Generation Partnership Project (3GPP)

2010-11-21T17:20:00.000-08:00

The GPRS recommendations belong to the GSM recommendations. The maintenance of all GSM recommendations is now handled within the Third Generation Partnership Project (3GPP) organization, the partners of which are:

ETSI, the European standardization entity;
Association of Radio Industries and Businesses (ARIB) and Telecommunication Technology Committee (TTC), the Japanese standardization entities;
Telecommunication Technology Association (TTA), the Korean standardization entity;
T1, the American standardization entity;
China Wireless Telecommunication Standard (CWTS) group, the Chinese standardization entity.

These standardization bodies have decided to collaborate within the 3GPP organization in order to produce specifications for a third-generation mobile system. At the beginning, the 3GPP organization was in charge of all specifications related to the third-generation mobile system for radio access technologies called Universal Terrestrial Radio Access (UTRA) and for evolution of GSM core networks.

Since August 2000, specifications related to GSM radio access are also the responsibility of the 3GPP. The 3GPP takes the place of the former Special Mobile Group (SMG) GSM organization. The 3GPP is organized around technical specification groups (TSGs) that deal with the following subjects:

TSG SA (Service Architecture), dealing with service, architecture, security, and speech coding aspects;
TSG RAN (Radio Access Network), focusing on UTRA radio access technologies;
TSG CN (Core Network), dealing with core network specifications;
TSG T (Terminal), covering applications, tests for 3G mobiles, and the USIM card;
TSG GERAN (GSM EDGE Radio Access Network), focusing on GSM radio interface, A and Gb interfaces.

Thus GSM evolutions as GPRS are treated in all TSGs except TSG RAN, which deals exclusively with UTRAN access technologies such as frequency division duplex (FDD), time-division duplex (TDD), and CDMA 2000. The TSG GERAN deals exclusively with the GSM radio interface evolutions and with A and Gb interfaces. The 3GPP recommendations are ranked according to a version reference.

Each new version of 3GPP recommendations contains a list of new features or a list of improvements on existing features. Initially, the GSM recommendations versions were referenced in the following order: Phase 1; Phase 2; Release 96; Release 97; Release 98; Release 99. As the reference year for the new version of phase 2++ recommendations no longer matched the release year of these specifications, it was decided that the versions following Release 99 will be referenced according to a version number, Release 4 being the first new version reference.

The GSM recommendations are organized up to Release 99 in the following series:

01 series: General;
02 series: Service Aspects;
03 series: Network Aspects;
04 series: MS-BS Interface and Protocols;
05 series: Physical Layer on the Radio Path;
06 series: Speech Coding Specification;
07 series: Terminal Adaptors for MSs;
08 series: BS-MSC Interface;
09 series: Network Interworking;
11 series: Equipment and Type Approval Specification;
12 series: Operation and Maintenance.

Each of the series contains a list of specifications identified by numbers. A given specification is therefore defined by its series number, followed by a recommendation number. For example, the 05.03 specification belongs to the physical layer on the radio path, and deals with channel coding issues.

In Release 4 of the 3GPP recommendations, the former GSM 01, 02, 03, 04, 05, and 06 series were kept for all GSM features that have not evolved with the third generation. From Release 4, these GSM series numbers were replaced by new series numbers, to be compliant with the 3GPP numbering. New series numbers can easily be deduced by adding 40 to the GSM series. Thus the 05 series describing the physical layer on the radio path become the 45 series from release 4. Also, the specification numbers in each series are deduced from the previous numbers by inserting a 0 as the first number. Thus, the R99 05.03 becomes the 45.003 from R4. Note that the different releases are continuously maintained.

The GPRS feature was introduced in Release 97 of the 3GPP recommendations. The GPRS recommendations are organized in three stages, as are all 3GPP recommendations:

Stage 1: Description of GPRS services;
Stage 2: Description of GPRS general architecture;
Stage 3: Detailed description of different equipment implemented for GPRS with their external interfaces.

The Stage 1 GPRS recommendations describe the services that will be provided by GPRS. The service description is given in the 02 series recommendations for Release 97 and Release 98 of the 3GPP recommendations and in the 22 series recommendations from Release 99. The evolution of GPRS services is discussed in Working Group 1 (WG1) of TSG SA within the 3GPP.

The stage 2 GPRS recommendations describe the general architecture of GPRS, with nodes implemented in the network and the interface mechanisms between these nodes. The description of the architecture is given in the 03 series of the recommendations for Release 97 and Release 98 of the 3GPP recommendations and in 23 series recommendations from Release 99. The evolution of GPRS architecture is discussed in WG2 of TSG SA within the 3GPP.

The stage 3 GPRS recommendations describe in a detailed manner the equipment and its external interfaces implemented in the network for GPRS (see 04, 05, 06, and 08 series recommendations up to Release 99, and then 44, 45, and 46 series recommendations from Release 4). The evolution of the behavior of this equipment is discussed in working groups of several associated TSGs.

Quality of GSM Service

2010-11-21T17:19:00.003-08:00

The network associates a certain quality of service (QoS) with each data transmission in GPRS packet mode. The appropriate QoS is characterized according to a number of attributes negotiated between the MS and the network. A first list of attributes is defined in Release 97/98 of the 3GPP recommendations. It was replaced in the release 99 by new attributes.

In Release 97/98 of the 3GPP recommendations, QoS is defined according to the following attributes:

Precedence class. This indicates the packet transfer priority under abnormal conditions, as for example during a network congestion load.
Reliability class. This indicates the transmission characteristics; it defines the probability of data loss, data delivered out of sequence, duplicate data delivery, and corrupted data. This parameter enables the configuration of layer 2 protocols in acknowledged or unacknowledged modes.
Peak throughput class. This indicates the expected maximum data transfer rate across the network for a specific access to an external packet switching network (from 8 to 2,048 Kbps).
Mean throughput class. This indicates the average data transfer rate across the network during the remaining lifetime of a specific access to an external packet switching network (best effort, from 0.22 bps to 111 Kbps).
Delay class. This defines the end-to-end transfer delay for the transmission of service data units (SDUs) through the GPRS network. The SDU represents the data unit accepted by the upper layer of GPRS and conveyed through the GPRS network. Table 2.1 shows the delay classes.

The delay class for data transfer gives some information about the number of resources that have to be allocated for a given service. Predictive value in delay class means that the network is able to ensure an end-to-end delay time for the transmission of SDUs; best effort means that the network is not able to ensure a value for an end-to-end transfer delay; in this case transmission of SDUs depends on network load.

The attributes of GPRS QoS were modified in Release 99 of the 3GPP recommendations in order to be identical to the ones defined for UMTS. The attributes described below apply to both GPRS and UMTS standards. Four classes of traffic have been defined for QoS:

Conversational class. These services are dedicated to bidirectional communication in real time (e.g., voice over IP and videoconferencing).
Streaming class. These services are dedicated to unidirectional data transfer in real time (e.g., audio streaming, one-way video).
Interactive class. These services are dedicated to the transport of human or machine interaction with remote equipment (e.g., Web browsing, access to a server, access to a database).
Background class. These services are dedicated to machine-to-machine communication that is not delay sensitive (e.g., e-mail and SMS).

The Release 99 of 3GPP recommendations defines attributes for QoS such as traffic class, delivery order, SDU format information, SDU error ratio, maximum SDU size, maximum bit rate for uplink, maximum bit rate for downlink, residual bit error ratio, transfer delay, traffic-handling priority, allocation/retention priority, and guaranteed bit rate for uplink and guaranteed bit rate for downlink.

Traffic class indicates the application type (conversational, streaming, interactive, background).
Delivery order indicates if there is in-sequence SDU delivery or not.
Delivery of erroneous SDUs indicates if erroneous SDUs are delivered or discarded.
SDU format information indicates the possible exact sizes of SDUs.
SDU error ratio indicates the maximum allowed fraction of SDUs lost or detected as erroneous.
Maximum SDU size indicates the maximum allowed SDU size (from 10 octets to 1,520 octets).
Maximum bit rate for uplink indicates the maximum number of bits delivered to the network within a period of time (from 0 to 8,640 Kbps).
Maximum bit rate for downlink indicates the maximum number of bits delivered by the network within a period of time (from 0 to 8,640 Kbps).
Residual bit error ratio indicates the undetected bit error ratio for each subflow in the delivered SDUs.
Transfer delay indicates the maximum time of SDU transfer for 95th percentile of the distribution of delay for all delivered SDUs.
Traffic-handling priority indicates the relative importance of all SDUs belonging to a specific GPRS bearer compared with all SDUs of other GPRS bearers.
Allocation/retention priority indicates the relative importance of resource allocation and resource retention for the data flow related to a specific GPRS bearer compared with the data flows of other GPRS bearers (useful when resources are scarce).
Guaranteed bit rate for uplink indicates the guaranteed number of bits delivered to the network within a period of time (from 0 to 8,640 Kbps).
Guaranteed bit rate for downlink indicates the guaranteed number of bits delivered to the network within a period of time (from 0 to 8,640 Kbps).

Use of GPRS

2010-11-21T17:19:00.001-08:00

The GPRS provides a set of GSM services for data transmission in packet mode within a PLMN. In packet-switched mode, no permanent connection is established between the mobile and the external network during data transfer. Instead, in circuit-switched mode, a connection is established during the transfer duration between the calling entity and the called entity. In packet-switched mode, data is transferred in data blocks, called packets.

When the transmission of packets is needed, a channel is allocated, but it is released immediately after. This method increases the network capacity. Indeed, several users can share a given channel, since it is not allocated to a single user during an entire call period. One of the main purposes of GPRS is to facilitate the interconnection between a mobile and the other packet-switched networks, which opens the doors to the world of the Internet.

With the introduction of packet mode, mobile telephony and Internet converge to become mobile Internet technology. This technology introduced in mobile phones allows users to have access to new value-added services, including:

Client-server services, which enable access to data stored in databases. The most famous example of this is access to the World Wide Web (WWW) through a browser.
Messaging services, intended for user-to-user communication between individual users via storage servers for message handling. Multimedia Messaging Service (MMS) is an example of a well-known messaging application.
Real-time conversational services, which provide bidirectional communication in real-time. A number of Internet and multimedia applications require this scheme such as voice over IP and video conferencing.
Tele-action services, which are characterized by short transactions and are required for services such as SMS, electronic monitoring, surveillance systems, and lottery transactions.

GPRS allows for radio resource optimization by using packet switching for data applications that may present the following transmission characteristics:

Infrequent data transmission, as when the time between two transmissions exceeds the average transfer delay (e.g., messaging services);
Frequent transmission of small data blocks, in processes of several transactions of less than 500 octets per minute (e.g., downloading of several HTML pages from a browsing application);
Infrequent transmission of larger data blocks, in processes of several transactions per hour (e.g., access of information stored in database centers);
Asymmetrical throughput between uplink and downlink, such as for data retrieval in a server where the uplink is used to send signaling commands and the downlink is used to receive data as a response of the request (e.g., WEB/WAP browser).

As the GPRS operator optimizes radio resources by sharing them between several users, he is able to propose more attractive fees for data transmission in GPRS mode than in circuit-switched mode. Indeed, the invoicing in circuit-switched mode takes into account the connection time between the calling user and the called user. Studies on data transmission show that data are exchanged from end to end during 20% of a circuit-switched connection time.

For example, a user browses the WWW, downloads an HTML page identified by a uniform resource locator (URL), reads the content of the HTML page, then downloads a new HTML page to read. In this example no data is exchanged from end to end between the two HTML page downloads. For this type of application, a more appropriate invoicing would take into account the volume of data exchanged instead of the circuit-switched connection time. In packet mode, the GPRS user may be invoiced according to the requested service type, the volume of data exchanged.

Logical Channels of GSM Radio Interface

2010-11-21T17:18:00.005-08:00

The association of a radio frequency channel and a time slot-the pair ARFCN and TN-uniquely defines a physical channel on both the uplink and the downlink. On top of the physical channels, logical channels ar mapped to convey the information of voice, data, and signaling. This signaling information is used for setting up a call, or to adapt the link to rapidly changing radio conditions, or to manage handovers, to give a few examples.

Logical channels can be seen as pipes, each one used for a different purpose by the higher layers of the system. Two types of logical channels exist, traffic channels and control channels. Among the control channels, according to their functions, four classes are defined: broadcast, dedicated, common, and associated. A broadcast channel is used by the network (in downlink only) to send general information to the MSs.

A channel is said to be dedicated if only one MS can transmit or receive in the ARFCN-TN defining this channel, and common if it carries information for several mobiles. An associated control channel is allocated to one mobile, in addition to a dedicated channel, and carries signaling for the operation of this channel. The purposes of the beacon are:

To allow a synchronization in time and frequency of the MSs to the BTS. This synchronization is needed by the MS to access the services of a cell.
To help the mobile in estimating the quality of the link during a communication, by measurements on the received signal from the BTS it is transmitting to, and from the other BTSs of the geographical area. These measurements are used by the network to determine when a handover is necessary, and to which BTS this handover should apply.
To help the mobile in the selection of a cell when it is in idle mode (that is, not in communication, but still synchronized to the system and able to receive an incoming call or to initiate a call). This selection is performed on the basis of the received power measurements made on the adjacent cells' beacon channels.
To access the general parameters of the cell needed for the procedures applied by the MS, or general information concerning the cell, such as its identification, the beacon frequencies of the surrounding cells, or the option supported by the cell (services).

To allow these various operations, the logical channels transmitted on the beacon are:

The broadcast control channel (BCCH), which continually broadcasts, on the downlink, general information on the cell, including base station identity, frequency allocations, and frequency-hopping sequences. The information is transmitted within system information (SI) blocks, which can be of different types according to the information that is carried out. The frequency with which an SI is retransmitted on the BCCH varies with the type of information.
The frequency control channel (FCCH), used by the MS to adjust its local oscillator (LO) to the BTS oscillator, in order to have a frequency synchronization between the MS and the BTS.
The synchronization channel (SCH), used by the MS to synchronize in time with the BTS, and to identify the cell.

As listed below, four channels comprise the common control channels (CCCH). Among these, the first three are used for the MS-initiated call or for call paging (notification of an incoming call toward the MS):

The random access channel (RACH) is used for the MS access requests to the network, for the establishment of a call, based on a slotted aloha method.
The paging channel (PCH) is defined to inform the MS of an incoming call.
The access grant channel (AGCH) is used to allocate some physical resource to a mobile for signaling, following a request on the RACH.
The cell broadcast channel (CBCH) may be used to broadcast specific news to the mobiles of a cell.

The dedicated control channels are:

The stand-alone dedicated control channel (SDCCH), utilized for registration, authentication, call setup, and location updating.
The slow associated control channel (SACCH), which carries signaling for the TCH or SDCCH with which it corresponds. The information that is transmitted on this channel concerns the radio link control (RLC), such as the power control on the corresponding TCH or SDCCH, or the time synchronization between the MS and the BTS.
The fast associated control channel (FACCH), carries the signaling that must be sent by the network to the MS to notify that a handover is occurring.

The TCHs can be of several types, according to the service that is accessed by the subscribers: voice or data, with various possible data rates.

General Characteristics of GSM Radio Interface

2010-11-21T17:18:00.003-08:00

Currently, there are several types of networks in the world using the GSM standard, but at different frequencies.

The GSM-900 is the most common in Europe and the rest of the world. Its extension is E-GSM.
The DCS-1800 operates in the 1,800-MHz band and is used mainly in Europe, usually to cover urban areas. It was also introduced to avoid saturation problems with the GSM-900.
The PCS-1900 is used primarily in North America.
The GSM-850 is under development in America.
The GSM-400 is intended for deployment in Scandinavian countries in the band previously used for the analog Nordic Mobile Telephony (NMT) system.

The system is based on frequency-division duplex (FDD), which means that the uplink (radio link from the mobile to the network-that is, mobile transmit, base receive), and downlink (from the network to the mobile-that is, base transmit, mobile receive) are transmitted on different frequency bands. For instance, in the 900-MHz E-GSM band, the block 880-915 MHz is used for transmission from mobiles to network, and the block 925-960 MHz is used for the transmission from network to mobiles.

Operators may implement networks that operate on a combination of the frequency bands listed above to support multiband mobile terminals. There are different ways of sharing the physical resource among all the users in a radio system, and this is called the multiple-access method. The multiple-access scheme defines how simultaneous communications share the GSM radio spectrum. The various multiple-access techniques in use in radio systems are frequency-division multiple access (FDMA), TDMA, and code-division multiple access (CDMA). GSM is based on both FDMA and TDMA techniques.

FDMA consists in dividing the frequency band of the system into several channels. In GSM, each RF channel has a bandwidth of 200 kHz, which is used to convey radio modulated signals, or carriers. Each pair of uplink/ downlink channels is called an absolute radio frequency channel (ARFC) and is assigned an ARFC number (ARFCN). The mapping of each ARFCN on the corresponding carrier frequency is given in.

TDMA is the division of the time into intervals: within a frequency channel, the time is divided into time slots. This division allows several users (eight) to be multiplexed on the same carrier frequency, each user being assigned a single time slot. A packet of data information, called a burst, is transmitted during a time slot. The succession of eight time slots is called a TDMA frame, and each time slot belonging to a TDMA frame is identified by a time slot number (TN), from 0 to 7.

GSM Network Architecture

2010-11-21T17:18:00.001-08:00

The structure of a GSM network relies on several functional entities, which have been specified in terms of functions and interfaces. It involves three main subsystems, each containing functional units and interconnected with the others through a series of standard interfaces.

The MS, the handheld mobile terminal;
The base station subsystem (BSS), which controls the radio link with the MS;
The network and switching subsystem (NSS), which manages the function of connection switching to other fixed public network or mobile network subscribers, and handles the databases required for mobility management and for the subscriber data.

As can be seen from the figure, in a PLMN, the radio access network part (BSS) is logically separated from the core network (NSS), in order to ease the standardization of the different functions.

MS

The MS is made up of the mobile equipment (ME), and a SIM. It performs the following functions:

Radio transmission and reception;
Source and channel coding and decoding, modulation and demodulation;
Audio functions (amplifiers, microphone, earphone);
Protocols to handle radio functions: power control, frequency hopping, rules for access to the radio medium;
Protocol to handle call control and mobility; Security algorithms (encryption techniques).

As mentioned, the SIM enables the user to have access to subscribed services irrespective of a specific terminal. The insertion of the SIM card into any GSM terminal allows the user to receive calls on that terminal, to make calls from that terminal, and to use the other subscribed services. The ME is identified with an international mobile equipment identity (IMEI).

The SIM card contains, among other information, the international mobile subscriber identity (IMSI) used to identify the subscriber to the system, and a secret key for authentication. The IMEI and the IMSI are independent, thereby allowing personal mobility.

BSS

The BSS is composed of several base station controllers (BSCs) and BTS. These two elements communicate across the Abis interface. The BTS contains the radio transceivers, responsible for the radio transmissions with the MS. This includes the following functions:

Modulation and demodulation;
Channel coding and decoding;
Encryption process;
RF transmit and receive circuits (power control, frequency hopping, management of antenna diversity, discontinuous transmission).

Several types of BTS exist: the normal BTS, the micro BTS, and the pico BTS. The micro BTS is different from a normal BTS in two ways. First, the range requirements are reduced, and the close proximity requirements are more stringent. Second, the micro BTS is required to be small and affordable in order to allow external street deployment in large numbers. The pico BTS is an extension of the micro BTS concept to the indoor environments.

The RF performances of these different BTSs are slightly different. The BSC manages the radio resources for one or more BTSs. It handles the management of the radio resource, and as such it controls the following functions: allocation and release of radio channels, frequency hopping, power control algorithms, handover management, choice of the encryption algorithm, and monitoring of the radio link.

Network Subsystem

The mobile services switching center (MSC) is the central part of the network subsystem (NSS). It is responsible for the switching of calls between the mobile users (between different BSCs or toward another MSC) and between mobile and fixed network users.

It manages outgoing and incoming calls from various types of networks, such as PSTN, ISDN, and PDN. It also handles the functionality required for the registration and authentication of a user, and the mobility operations. This includes location updating, inter-MSC handovers, and call routing. The BSS communicates with the MSC across the A interface.

Associated with the MSC, two databases, the home location register (HLR) and the visitor location register (VLR), provide the call-routing and roaming capabilities. The HLR contains all the administrative information related to the registered subscribers within the GSM network. This includes the IMSI, which unequivocally identifies the subscriber within any GSM network, the MS ISDN number (MSISDN), and the list of services subscribed by the user (such as voice, data service).

The HLR also stores the current location of the MS, by means of the address of the VLR in which it is registered. The VLR temporarily keeps the administrative data of the subscribers that are currently located in a given geographical area under its control. Each functional entity may be implemented as an independent unit, but most of the time, the VLR is colocated with the MSC, so that the geographical area controlled by the MSC corresponds to that controlled by the VLR.

The MSC contains no information about particular MSs, but rather, the information is stored in the location registers. Two other registers are used for authentication and security purposes:

The equipment identity register (EIR) is a database that contains a list of all valid ME on the network, where each MS is identified by its IMEI. An IMEI is marked as invalid if it has been reported stolen.
The authentication center (AuC) is a protected database that contains a copy of the secret key stored in each subscriber's SIM card, for authentication and encryption over the radio channel. The AuC verifies if a legitimate subscriber has requested a service. It provides the codes for both authentication and encryption to avoid undesired violations of the system by third parties.

Two other important entities of the NSS are the operations and maintenance center (OMC) and the network management center (NMC). These entities perform the functions relative to the network management (NM), such as the configuration of the system (locally or remotely), maintenance and tests of the pieces of equipment, billing, statistics on the performance, and gathering of all information related to subscriber traffic necessary for invoicing and administration of subscribers.

GSM Services

2010-11-21T17:17:00.003-08:00

In the specification of a telecommunication standard such as GSM, the first step is of course the definition of the services offered by the system. GSM is a digital cellular system designed to support a wide variety of services, depending on the user contract and the network and mobile equipment capabilities. In GSM terminology, telecommunication services are divided into two broad categories:

Bearer services are telecommunication services providing the capability of transmission of signals between access points [the user-network interfaces (UNIs) in ISDN]. For instance, synchronous dedicated packet data access is a bearer service.
Teleservices are telecommunication services providing the complete capability, including terminal equipment functions, for communication between users according to protocols established by agreement between network operators.

In addition to these services, supplementary services are defined that modify or supplement a basic telecommunication service.

Bearer Services

There exist several categories of bearer services:

Unrestricted digital information (UDI) is designed to offer a peer-to-peer digital link.
The 3.1 kHz is external to the PLMN and provides a UDI service on the GSM network, interconnected with the ISDN or the PSTN by means of a modem.
PAD allows an asynchronous connection to a packet assembler/disassembler (PAD). This enables the PLMN subscribers to access a packet-switched public data network (PSPDN).
Packet enables a synchronous connection to access a PSPDN network and alternate speech and data, providing the capability to switch between voice and data during a call.
Speech followed by data first provides a speech connection, and then allows to switch during the call for a data connection. The user cannot switch back to speech after the data portion.

Teleservices

In terms of application, teleservices correspond to the association of a particular terminal to one or several bearer services. They provide access to two kinds of applications:

Between two compatible terminals;
From an access point of the PLMN to a system including high-level functions, for example, a server.

Of course, the most basic teleservice supported by GSM is digital voice telephony, based on transmission of the digitally encoded voice over the radio. The voice service also includes emergency calls, for which the nearest emergency-service provider is notified by dialing three digits. The other teleservices that are defined for a PLMN are:

Data services, with data rates ranging from 2.4 Kbps to 14.4 Kbps. These services are based on circuit-switched technology. Circuit switched means that during the communication, a circuit is established between two entities for the transfer of data. The physical resource is used during the whole duration of the call.
Short message service (SMS), which is a bidirectional service for short alphanumeric (up to 160 bytes) messages.
Access to a voice message service.
Fax transmission.

Supplementary Services

Supplementary services include several forms of call forward (such as call forwarding when the mobile subscriber is unreachable by the network), caller identification, call waiting, multiparty conversations, charging information, and call barring of outgoing or incoming calls. These call-barring features can be used for example when roaming in another country, if the user wants to limit the communication fees.

GSM General Concepts

2010-11-21T17:17:00.001-08:00

First-generation telephony systems were analog. During the early 1980s these systems underwent rapid development in Europe. Although the NMT system was used by all the Nordic countries, and the TACS system in the United Kingdom and Italy, there was a variety of systems and no compatibility among them. Compared with these systems, the main advantages offered by GSM, which is the most important of the second-generation digital systems, are:

Standardization;
Capacity;
Quality;
Security.

Standardization guarantees compatibility among systems of different countries, allowing subscribers to use their own terminals in those countries that have adopted the digital standard. The lack of standardization in the first-generation system limited service to within the borders of a country. Mobility is improved, since roaming is no longer limited to areas covered by a certain system. Calls can be charged and handled using the same personal number even when the subscriber moves from one country to another.

Standardization also allows the operator to buy entities of the network from different vendors, since the functional elements of the network and the interfaces between these elements are standardized. This means that a mobile phone from any manufacturer is able to communicate with any network, even if this network is built with entities from different vendors. This leads to a large economy of scale and results in cost reduction for both the operator and the subscriber. Furthermore, the phone cost is also reduced, because as GSM is an international standard, produced quantities are greater and the level of competition is high.

With respect to capacity, the use of the radio resource is much more efficient in a digital system such as GSM than in an analog system. This means that more users can be allocated in the same frequency bandwidth. This is possible with the use of advanced digital techniques, such as voice compression algorithms, channel coding, and multiple access techniques. Note that capacity gains are also achieved with radio frequency reuse, which had also been used in analog systems.

The quality in digital transmission systems is better, thanks to the channel coding schemes that increase the robustness in the face of noise and disturbances such as interference caused by other users or other systems. The quality improvement is also due to the improved control of the radio link, and adaptations to propagation conditions, with advanced techniques such as power control or frequency hopping.

In terms of security, powerful authentication and encryption techniques for voice and data communications are enabled with GSM, which guarantees protected access to the network, and confidentiality.

Cellular Telephony

In mobile radio systems, one of the most important factors is the frequency spectrum. In order to make the best use of the bandwidth, the system is designed by means of the division of the service area into neighboring zones, or cells, which in theory have a hexagonal shape. Each cell has a base transceiver station (BTS), which to avoid interference operates on a set of radio channels different from those of the adjacent cells.

This division allows for the use of the same frequencies in nonadjacent cells. A group of cells that as a whole use the entire radio spectrum available to the operator is referred to as a cluster. The shape of a cell is irregular, depending on the availability of a spot for the BTS, the geography of the terrain, the propagation of the radio signal in the presence of obstacles, and so on.

In dense urban areas, for instance, where the mobile telephony traffic is important, the diameter of the cells is often reduced in order to increase capacity. This is allowed since the same frequency channels are used in a smaller area. On the other hand, reducing the cell diameter leads to a decrease in the distance necessary to reuse the frequencies (that is, the distance between two cochannel cells), increasing cochannel interference. In order to minimize the level of interference, several techniques are used on the radio interface.

Public Land Mobile Network

A public land mobile network (PLMN) is a network established for the purpose of providing land mobile telecommunications services to the public. It may be considered as an extension of a fixed network, such as the Public Switched Telephone Network (PSTN), or as an integral part of the PSTN.

Multiband Mobile Phones

Because of the increasing demand on the mobile networks, today the mobile stations (MSs) tend to be multiband. Indeed, to avoid network saturation in densely populated regions, mobile phones capable of supporting different frequency bands have been implemented, to allow for the user making communications in any area, at any time.

A dual-band phone can operate in two different frequency bands of the same technology, for instance in the 900-MHz and 1800-MHz frequency bands of the GSM system. Triple-band mobile phones have also come on the market, with the support of GSM-900 (900-MHz GSM band), DCS-1800 (1800-MHz GSM band), and PCS-1900 (1900-MHz GSM band), for example.

Note that DCS-1800 and PCS-1900 are never deployed in the same country, and therefore this kind of phone can be used by travelers who want to have service coverage in a large number of countries.

SIM Card

One of the most interesting innovations of GSM is that the subscriber's data is not maintained in the mobile phone. Rather a "smart card," called a subscriber identity module (SIM) card, is used. The SIM is inserted in the phone to allow the communications. A user may thus make telephone calls with a mobile phone that is not his own, or have several phones but only one contract.

It is for example possible to use a SIM card in a different mobile when traveling to a country that has adopted the GSM on a different frequency band. A European can therefore rent a PCS1900 phone when traveling to the United States, while still using his own SIM card, and thus may receive or send calls. The SIM is used to keep names and phone numbers, in addition to those that are already kept in the phone's memory.

The card is also used for the protection of the subscriber, by means of a ciphering and authentication code.

Mobility

GSM is a cellular telephony system that supports mobility over a large area. Unlike cordless telephony systems, it provides location, roaming, and handover.

Location Area - The ability to locate a user is not supported in first-generation cellular systems. This means that when a mobile is called, the network has to broadcast the notification of this call in all the radio coverage. In GSM, however, location areas (LAs), which are groups of cells, are defined by the operator. The system is able to identify the LA in which the subscriber is located. This way, when a user receives a call, the notification (or paging) is only transmitted in this area. This is far more efficient, since the physical resource use is limited.

Roaming - In particular, the GSM system has the capability of international roaming, or the ability to make and receive phone calls to and from other nations as if one had never left home. This is possible because bilateral agreements have been signed between the different operators, to allow GSM mobile clients to take advantage of GSM services with the same subscription when traveling to different countries, as if they had a subscription to the local network.

To allow this, the SIM card contains a list of the networks with which a roaming agreement exists. When a user is "roaming" to a foreign country, the mobile phone automatically starts a search for a network stipulated on the SIM card list. The choice of a network is performed automatically, and if more than one network is given in the list, the choice is based on the order in which the operators appear. This order can be changed by the user.

The home PLMN is the network in which the user has subscribed, while the visited PLMN often refers to the PLMN in which the user is roaming. When a user receives a call on a visited PLMN, the transfer of the call from the home PLMN to the visited PLMN is charged to the called user by his operator.

Handover - When the user is moving from one cell to the other during a call, the radio link between BTS 1 and the MS can be replaced by another link, between BTS 2 and the MS. The continuity of the call can be performed in a seamless way for the user. This is called handover. With respect to dual-band telephones, one interesting feature is called the dual-band handover. It allows the user in an area covered both by the GSM-900 and by the DCS-1800 frequency bands, for instance, to be able to transfer automatically from one system to the other in the middle of a call.

Beacon Channel

For each BTS of a GSM network, one frequency channel is used to broadcast general signaling information about this cell. This particular carrier frequency is called a beacon channel, and it is transmitted by the BTS with the maximum power used in the cell, so that every MS in the cell is able to receive it.

MS Idle Mode

When it is not in communication, but still powered on, the MS is said to be in idle mode. This means that it is in a low consumption mode, but synchronized to the network and able to receive or initiate calls.

Birth of the GSM System

2010-11-21T17:16:00.001-08:00

The first step in the history of GSM development was achieved back in 1979, at the World Administrative Radio Conference, with the reservation of the 900-MHz band. In 1982 at the Conference of European Posts and Telegraphs (CEPT) in Stockholm, the Groupe Spécial Mobile was created, to implement a common mobile phone service in Europe on this 900-MHz frequency band.

Currently the acronym GSM stands for Global System for Mobile Communication; the term "global" was preferred due to the intended adoption of this standard in every continent of the world. The proposed system had to meet certain criteria, such as:

Good subjective speech quality (similar to the fixed network);
Affordability of handheld terminals and service;
Adaptability of handsets from country to country;
Support for wide range of new services;
Spectral efficiency improved with respect to the existing first-generation analog systems;
Compatibility with the fixed voice network and the data networks such as ISDN;
Security of transmissions.

Digital technology was chosen to ensure call quality.

The basic design of the system was set by 1987, after numerous discussions led to the choice of key elements such as the narrowband time-division multiple access (TDMA) scheme, or the modulation technique. In 1989 responsibility for the GSM was transferred to the European Telecommunication Standards Institute (ETSI).

ETSI was asked by the EEC to unify European regulations in the telecommunications sector and in 1990 published phase I of the GSM system specifications (the phase 2 recommendations were published in 1995). The first GSM handset prototypes were presented in Geneva for Telecom '91, where a GSM network was also set up.

Commercial service had started by the end of 1991, and by 1993 there were 36 GSM networks in 22 countries. The system was standardized in Europe, but is now operational in more than 160 countries all over the world, and was adopted by 436 operators. The growth of subscribers has been tremendous, reaching 500 million by May 2001.

The thousands of pages of GSM recommendations, designed by operators and infrastructure and mobile vendors, provide enough standardization to guarantee proper interworking between the components of the system. This is achieved by means of the functional and interface descriptions for each of the different entities.

The GSM today is still under improvement, with the definition of new features and evolution of existing features. This permanent evolution is reflected in the organization of the recommendations, first published as phase I, then phase II and phase II+, and now published with one release each year (releases 96, 97, 98, 99, and releases 4 and 5 in 2000 and 2001). As stated, responsibility for the GSM specifications was carried by ETSI up to the end of 1999.

During 2000, the responsibility of the GSM recommendations was transferred to the Third Generation Partnership Project (3GPP). This world organization was created to produce the third-generation mobile system specifications and technical reports. The partners have agreed to cooperate in the maintenance and development of GSM technical specifications and technical reports, including evolved radio access technologies [e.g., General Packet Radio Service (GPRS) and Enhanced Data rates for Global Evolution (EDGE)].

Wireless Internet Service Providers

2010-11-12T18:29:00.001-08:00

Wireless Internet service providers (WISPs) use Wi-Fi technology to offer access to the Internet at speeds of up to 11 Mbps when users are in range of an antenna. Based on the IEEE 802.11b Standard, Wi-Fi technology is used by WISPs to provide wireless Internet access at airports, hotels, convention centers, coffee shops, and other public places.

Users download free software from the WISP’s Web page and use it to find an available signal (Figure W-3). On powering up a notebook computer equipped with a Wi-Fi-compatible IEEE 802.11b card, the software searches all available networks and establishes a wireless connection within seconds.

There are usually several service plans to chose from, according to the number of days the user expects to be online:

10-day connect package A package of 10 connect days a month, which includes unlimited access in a WISP’s service location for up to 24 hours. The user can even disconnect and reconnect within each 24-hour period from the same location with no additional charge. Each additional connect day is charged separately.

Unlimited usage Unlimited usage allows the user to stay connected to the wireless network all day every day for a fixed monthly charge.

Pay-as-you-go For users who are not sure how much they will use the service, they can sign up for the service and pay a daily charge instead of a monthly fee. Aconnect day includes unlimited access in a WISP’s service location for up to 24-hours. The user can disconnect and reconnect within each 24-hour period from the same location with no additional charge.

In addition to being able to connect to hundreds of hot spot locations, a monthly service plan also may include:

Wi-Fi “sniffer” software that checks the airwaves for available wireless networks.
Location directory to find service locations.
Web-based account management, allowing the user to manage his or her own account. Online and 800 number customer support is available.
Save and manage security keys and network settings.
Built-in personal virtual private network (VPN) to ensure secure connections to corporate networks.

Wi-Fi services are also offered by traditional ISPs such as Earthlink, giving customers another way to access their services while at public places where they can use the precious little time they have catching up on e-mail or connecting to the Internet.

Some cellular service providers are offering wireless data access via an integrated GPRS/EDGE/IEEE 802.11b service offering. By combining the benefits of their existing 2.5/3G and Wi-Fi networks, they expect to give customers what they want most from wireless data services: ubiquitous coverage and high speed.

Customers will have seamless service between the two wireless networks via a combo PC card for notebook computers that provides access to both GPRS/EDGE and IEEE 802.11b networks, giving them the ability to move between the two environments without having to change cards.

The existing GPRS and upcoming EDGE networks provide wide area coverage for applications where customers need constant access to such applications as e-mail and calendar, whereas Wi-Fi networks available in convenient public locations allow them to spend time accessing larger data files and multimedia messages or browse the Web.

Wireless Internet Access

2010-11-12T18:28:00.001-08:00

In most organizations today, Internet access via the LAN is the norm. Workers share applications, data, and services through their hub- or switch-based LAN connection. When they require Internet access to do research on the Web or send e-mail to someone on another network, for example, the traffic goes through a router connected to the hub or switch and then out to the ISP via a dedicated, “always on” connection such as a Digital Subscriber Line (DSL) or T1 link or even cable.

Telecommuters may have to rely on dialup services that offer no more than 56 kbps. However, there are two trends that make the case for wireless Internet access. One trend has to do with the workforce itself; more and more workers are becoming mobile and require a flexible method of Internet access from wherever they happen to be. This greatly improves flexibility in that the user does not have to find an available phone line in order to dial into the Internet.

Wireless access to the Internet also increases productivity in that the user can accomplish work-related tasks at the most opportune time, even while traveling or taking a “vacation.” Second, more companies require high-speed Internet access and cannot always get ISDN, DSL, or cable in their areas or afford the price of one or more T1 lines.

Larger companies that require broadband Internet access in the multimegabit range via T3 or OC-3 may not be able to wait for fiber installation to their locations. These companies are looking to fixed wireless providers for fast installation as well as cheap bandwidth. Whereas a new fiber build may take months to complete under a best-case scenario, wireless broadband connectivity from the customer premises to the service provider’s hub antenna can be accomplished in a matter of days.

Business users have a growing number of wireless Internet access services to choose from, and vendors and service providers are emphasizing technologies designed to let users take the Internet with them wherever they go. Already, wireless offerings run the gamut from Wireless Application Protocol (WAP)–enabled mobile phones to broadband architectures that offer fixed wireless access to IP-based networks at megabit-per-second speeds.

In addition, Internet connectivity is now available with all major mobile phone protocols, including Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), and Global System for Mobile (GSM) telecommunications.

Wireless Access Methods

There are several methods to wirelessly access the Internet, including analog cellular and cellular digital packet data networks, packet radio services, and satellite.

Cellular Networks Analog cellular phone subscribers can send files and e-mail wirelessly via the Internet by hooking up a modem to their phones. Of course, this method of access requires that the user have a cell phone in the first place, as well as an adapter cable to connect the phone to the modem. Cellular modems work anywhere a cell phone does. The problem is that they work only as well as the cell phone does at any given moment.

Checking e-mail on the Internet can be slow, and connection quality varies from network to network. To access Web content on the Internet, however, really requires a digital cellular service [also called Personal Communication Service (PCS)] and a special phone equipped with a liquid-crystal display (LCD) screen. AT&T’s PocketNet phone, for example, lets users access the Internet in areas served by its Cellular Digital Packet Data (CDPD) network.

With this type of cellular service, standard analog cell phones will not work; a digital CDPD phone is required. An alternative is to use a dual-mode phone that operates in standard analog cellular mode for voice conversations and CDPD mode for access to the Internet at 19.2 kbps. AT&T’s PocketNet service includes a personal information manager (PIM) that contains an address book, calendar, and to-do list that are maintained on AT&T’s Web site and accessed through the phone.

The personal address book is tied to the PocketNet phone’s “easy dialing” feature for fast, convenient calling. Another feature offered by CDPD is mobility management, which routes messages to users regardless of the location or the technology. Gateways provide the cellular network with the capability to recognize when subscribers move out of the CDPD coverage area and transfer messages to them via circuit-switched cellular.

Packet Radio Networks An example of a radio network is provided by the Ricochet service developed by Metricom, now a subsidiary of Aerie Networks, that provides network solutions and wireless data communications for industrial and PC applications. The Ricochet service comprises radios, wired access points (AP), and network interconnection facilities (NIF) that enable data to be sent across a network of intelligent radio nodes at speeds of over 176 kbps, with bursts of up to 400 kbps.

The network uses frequency-hopping spread-spectrum packet radios. Alarge number of these low-power radios are installed throughout a geographic region in a mesh topology, usually placed on top of streetlights or utility poles. These radio receivers, about the size of a shoebox, are also referred to as “microcell radios.”

Only a small amount of power is required for the radio, which is received by connecting a special adapter to the streetlight. No special wiring is required. These radios are placed about every quarter to a half mile and take only about 5 minutes each to install. Using 162 frequency- hopping channels in a random pattern accommodates many users at the same time, along with providing a high degree of security.

Distributed among the radios are APs, which are used to route the wireless packets on to the wired backbone. Gathering and converting the packets so that they can be transmitted to the wired backbone is accomplished via a T1- based Frame Relay connection. The packets can then be sent to another AP, the Internet, or the appropriate service provider. If the packet is sent to another WAP, it is being used as an alternate route through the mesh.

The number of paths a packet can take through the network enhances speed throughput, since network blockage is not as frequent and many possible repeaters exist for the packet. The Ricochet modem weighs only 8 ounces and thus is very portable. It can be plugged into the serial port of a computer and can be connected to online services and networks just like a standard phone modem.

The modem works with most communications software, as well as with Intel-based and Macintosh hardware platforms and operating systems. Ricochet’s wired backbone is based on standard Internet Protocol (IP) technology, routing data via a metropolitan service area. If a data packet has to move across the country, Ricochet’s NIF system is used. The NIF functions as a router, collecting packets from the WAPs and using leased lines to connect with NIFs situated in the different metropolitan areas.

A name server is part of the Ricochet network backbone, providing security by validating all connection requests. Metricom had been testing a new wireless data technology that would have provided data rates equal to that provided by wired ISDN 128-kbps service. This technology, called Ricochet II, uses two bands of unlicensed spectrum: the 900- MHz band and the 2.4-GHz band.

The new network is compatible with the company’s existing Ricochet network and modems. After investing $1.3 billion in infrastructure, Metricom declared bankruptcy and discontinued operations in August 2001. Under new management, the company is in the process of reactivating the existing network and expanding Ricochet to areas where high-speed broadband access is currently unavailable.

The outlook for Ricochet is unclear. Newer, cheaper Wi-Fi networks are being set up that greatly surpasses the speed of Ricochet. In fact, a new type of wireless Internet service provider (WISP) has emerged, such as Boingo Wireless, which uses the 2.4-GHz frequency band to offer data rates of up to 11 Mbps in public places.

Fixed Wireless Access As an alternative to traditional wirebased local telephone service, fixed wireless access technology provides a wireless link to the Public Switched Telephone Network (PSTN). Unlike cellular technologies, however, which provide services to mobile users, fixed wireless services require a rooftop antenna to an office building or home that has a line of sight with a service provider’s hub antenna.

Fixed wireless access systems come in two varieties: narrowband and broadband. Anarrowband fixed wireless access service can provide bandwidth up to 128 kbps, which can support one voice conversation and a data session such as Internet access or fax transmission. Abroadband fixed wireless access service can provide bandwidth in the multimegabit-per-second range, which is enough to support telephone calls, television programming, and broadband Internet access.

A narrowband fixed wireless service requires a wireless access unit that is installed on the exterior of a home or business to allow customers to originate and receive calls with no change to their existing analog telephones. Voice and data calls are transmitted from the transceiver at the customer’s location to the base station equipment, which relays the call through carrier’s existing network facilities to the appropriate destination. No investment in special phones or facsimile machines is required; customers use all their existing equipment.

Narrowband fixed wireless systems use the licensed 3.5- GHz radio band with 100-MHz spacing between uplink and downlink frequencies. Subscribers receive network access over a radio link within a range of 200 meters (600 feet) to 40 kilometers (25 miles) of the carrier’s hub antenna. About 2000 subscribers can be supported per cell site. Broadband fixed wireless access systems are based on microwave technology.

Multichannel Multipoint Distribution Service (MMDS) operates in the licensed 2- to 3-GHz frequency range, while Local Multipoint Distribution Service (LMDS) operates in the licensed 28- to 31-GHz frequency range. Both services are used by Competitive Local exchange Carriers (CLECs) primarily to offer broadband Internet access. These technologies are used to bring data traffic to the fiberoptic networks of Interexchange Carriers (IXCs) and nationwide CLECs, bypassing the local loops of the Incumbent Local Exchange Carriers (ILECs).

Fixed wireless access technology originated out of the need to contain carriers’ operating costs in rural areas, where pole and cable installation and maintenance are more expensive than in urban and suburban areas. However, wireless access technology also can be used in urban areas to bypass the local exchange carrier for long-distance calls. Since the IXC or CLEC avoids having to pay the ILEC’s local loop interconnection charges, the savings can be passed back to the customer. This arrangement is also referred to as a “wireless local loop.”

Satellite Services Satellites are another solution for the rapidly growing demand to transmit Internet and other networking traffic because they offer reliable connections to virtually anywhere in the world.

CyberStar, for example, offers a portfolio of business services, including a global broadband IP multicasting service that allows business users to send high-bandwidth voice, video, and data files to branch offices. By integrating IP, applications, video and audio streaming, IP multicast, Webcasting, and high-speed delivery onto an independent, satellite-based platform, CyberStar gives the IT manager a scalable broadband network.

The satellite service enhances, not replaces, existing enterprise communications infrastructures. The CyberStar system is intended as an overlay that fits with whatever companies are currently running. They can keep missioncritical applications on the current network and run dataintensive and media-rich applications over a reliable and cost-efficient satellite network.

Customers pay for the bandwidth they use rather than signing up for a flat-rate service. Pricing is based on the amount of traffic that is sent each month and the number of sites that are receiving that traffic. Customers are charged initial installation costs per site, which includes antennas, satellite receiver cards, and service activation fees. Other satellite service providers also support Internet traffic.

For homes and businesses, Hughes Network Systems (HNS) has given has been offering its one-way DirecPC Internet access service for several years as well as a newer one- and two-way broadband service, called DirecWAY, which offers 400 kbps. In the near future, low-earth-orbit (LEO) satellites such as Teledesic will provide Internet access and support other broadband applications with bandwidth on demand ranging from 64 kbps to multimegabit-per-second speeds.

Service Caveats

The biggest and most obvious concern to those interested in wireless technology is that it is more expensive than its wired counterpart and requires an investment in special equipment. As portability becomes more of a factor with regard to Internet access, corporations will become more willing to pay the higher cost of wireless technology. As history has shown, once prices drop due to corporate participation, consumers also will be able to reap the benefits of wireless technology.

Another concern is how network managers are going to integrate the wireless and wired worlds. This involves not only two skill sets, but also two network management systems and two separate application development paths. Nevertheless, wireless technology is becoming more accepted because it can now be economically integrated with wired networks. This can be done with wireless LAN access points that are connected to the hub or switch with Category 5 cable.

Performance is another issue that needs to be improved in wireless Internet access, particularly for real-time applications. The perception is that a wireless connection should have the same throughput and latency as a wired connection, but this is usually not possible. This tends to give the notion that there is not a reasonable response time for interactive applications with wireless connections.

While good response time can be had with fixed wireless systems that use MMDS and LMDS, these technologies have other issues that bear consideration, such as limited distance and a lineof- sight requirement. These technologies also falter during heavy rain, dense fog, and dust storms. While the service is out periodically, wired links for backup may be required.

As noted, there are some wireless Internet access providers that are starting to use the 2.4-GHz ISM (industrial, scientific, medical) frequency band to offer commercial Wi-Fi services. But this is unlicensed spectrum, which means that there is no guarantee against interference. MMDS and LMDS, on the other hand, are services provided over licensed spectrum. Since the FCC controls the use of this spectrum, business users can expect interference-free wireless connections for Internet access.

There are a variety of technologies available for wireless Internet access. Although wide-scale deployment of wireless Internet access services is still somewhere in the future, the long-term prospects for those services may be brighter than ever, due in large part to the number of carriers getting involved with the various technologies and the increasing investments being made toward further development.

In many parts of the United States, there is the growing realization that obtaining broadband Internet access through cable and DSL will not be available anytime soon, if ever. Wireless technologies have an important role to play on filling this niche.

Wireless Fidelity

2010-11-12T18:27:00.001-08:00

Wireless Fidelity (Wi-Fi) refers to a type of Ethernet specified under the IEEE 802.11a and IEEE 802.11b Standards for LANs operating in the 5- and 2.4-GHz unlicensed frequency bands respectively. Wi-Fi is equally suited to residential users and businesses, and equipment is available that allows both bands to be used to support separate networks simultaneously.

The IEEE 802.11 Standard makes the wireless network a straightforward extension of the wired network. This has allowed for a very uncomplicated implementation of wireless communication with obvious benefits—they can be installed using the existing network infrastructure with minimal retraining or system changes. Notebook users can roam throughout their sites while remaining in contact with the network via strategically placed access points that are plugged into the wired network.

Wireless users can run the same network applications they use on an Ethernet LAN. Wireless adapter cards used on laptop and desktop systems support the same protocols as Ethernet adapter cards. For most users, there is no noticeable functional difference between a wired Ethernet desktop computer and a wireless computer equipped with a wireless adapter other than the added benefit of the ability to roam within the wireless cell.

Under many circumstances, it may be desirable for mobile network devices to link to a conventional Ethernet LAN in order to use servers, printers, or an Internet connection supplied through the wired LAN. Awireless access point (AP) is a device used to provide this link. The IEEE 802.11b Standard designates devices that operate in the 2.4-GHz band to provide a data rate of up to 11 Mbps at a range of up to 300 feet (100 meters) using directsequence spread-spectrum technology.

Some vendors have implemented proprietary extensions to the IEEE 802.11b Standard, allowing applications to burst beyond 11 Mbps to reach as much as 22 Mbps. Users can share files and applications, exchange e-mail, access printers, share access to the Internet, and perform any other task as if they were directly cabled to the network. The IEEE 802.11a Standard designates devices that operate in the 5-GHz band to provide a data rate of up to 54 Mbps at a range of up to 900 feet (300 meters).

Sometimes called “Wi-Fi5,” this amount of bandwidth allows users to transfer large files quickly or even watch a movie in MPEG format over the network without noticeable delays. This technology works by transmitting high-speed digital data over a radio wave using Orthogonal Frequency Division Multiplexing (OFDM) technology. OFDM works by splitting the radio signal into multiple smaller subsignals that are then transmitted simultaneously at different frequencies to the receiver.

OFDM reduces the amount of interference in signal transmissions, which results in a high-quality connection. Wi-Fi5 products automatically sense the best possible connection speed to ensure the greatest speed and range possible with the technology. Some vendors have implemented proprietary extensions to the IEEE 802.11a Standard allowing applications to burst beyond 54 Mbps to reach as much as 72 Mbps.

IEEE 802.11 wireless networks can be implemented in infrastructure mode or ad-hoc mode. In infrastructure mode—referred to in the IEEE specification as the “basic service set”—each wireless client computer associates with an AP via a radio link. The AP connects to the 10/100-Mbps Ethernet enterprise network using a standard Ethernet cable and provides the wireless client computer with access to the wired Ethernet network.

Ad-hoc mode is the peer-topeer network mode, which is suitable for very small instal lations. Ad-hoc mode is referred to in the IEEE 802.11b specification as the “independent basic service set.” Security for Wi-Fi networks is handled by the IEEE standard called Wired Equivalent Privacy (WEP), which is available in 64- and 128-bit versions. The more bits in the encryption key, the more difficult it is for hackers to decode the data.

It was originally believed that 128-bit encryption would be virtually impossible to break due to the large number of possible encryption keys. However, hackers have since developed methods to break 128-bit WEP without having to try each key combination, proving that this system is not totally secure. These methods are based on the ability to gather enough packets off the network using special eavesdropping equipment to then determine the encryption key.

Although WEP can be broken, it does take considerable effort and expertise to do so. To help thwart hackers, WEP should be enabled and the keys rotated on a frequent basis. The wireless LAN industry has recognized that WEP is not as secure as once thought and is responding by developing another standard, known as IEEE 802.11i, that will allow WEP to use the Advanced Encryption Algorithm (AES) to make the encryption key even more difficult to determine.

AES replaces the older 56-bit Digital Encryption Standard (DES), which had been in use since the 1970s. AES can be implemented in 128- , 192- , and 256-bit versions. Assuming a computer with enough processing power to test 255 keys per second, it would take 149 trillion years to crack AES.

Wi-Fi is a certification of interoperability for IEEE 802.11b systems awarded by the Wireless Ethernet Compatibility Alliance (WECA), now known as the Wi-Fi Alliance. The Wi- Fi seal indicates that a device has passed independent tests and will reliably interoperate with all other Wi-Fi certified equipment. Customers benefit from this standard by avoiding becoming locked into one vendor’s solution—they can purchase Wi-Fi certified access points and client devices from different vendors and still expect them to work together.

Wireless Communications Services

2010-11-12T18:26:00.001-08:00

Wireless Communications Services (WCS) is a category of service that operates in the 2.3-GHz band of the electromagnetic spectrum from 2305 to 2320 MHz and 2345 to 2360 MHz. The FCC issued licenses for WCS as the result of a spectrum auction held in April 1997. Licensees are permitted—within their assigned spectrum and geographic areas—to provide any fixed, mobile, radiolocation, or broadcast-satellite service.

One use for the WCS spectrum is for services that adhere to the Personal Access Communications System (PACS) standard. This standard is applied to consumer-oriented products, such as personal cordless devices. There are two 10-MHz WCS licenses for each of 52 major economic areas (MAEs) and two 5-MHz WCS licenses for each of 12 regional economic area groupings (REAGs).

WCS licensees are permitted to partition their service areas into smaller geographic service areas and to disaggregate their spectrum into smaller blocks without limitation. Licenses are good for a term of 10 years and are renewable just like PCS and cellular licensees. In addition, WCS licensees will be required to provide “substantial service” within their 10-year license term.

WCS is implemented through small relay stations, which may interface with the Public Switched Telephone Network (PSTN). Where WCS poses interference problems with existing Multipoint Distribution Service (MDS) or Instructional Television Fixed Service (ITFS) operations, the WCS licensees must bear the full financial obligation for the remedy.

WCS licensees must notify potentially affected MDS/ITFS licensees at least 30 days before commencing operations from any new WCS transmission site or increasing power from an existing site of the technical parameters of the WCS transmission facility. The FCC expects WCS and MDS/ITFS licensees to coordinate voluntarily and in good faith to avoid interference problems, which will result in the greatest operational flexibility in each of these types of operations.

In establishing WCS, the FCC believed that the flexible use of the 2305- to 2320-MHz and 2345- to 2360-MHz frequency bands would help ensure that new technologies are developed and deployed, such as a wireless system tailored to provide portable Internet access over wide areas at data rates comparable to an ISDN-type connection.

Because the technical characteristics of such a system would differ significantly from those for some other systems that might use this band (e.g., PCS), the FCC neither restricted the services provided in this band nor dictated technical standards for operation beyond those required to avoid interference and protect the public interest. In fact, WCS licensees are not constrained to a single use of this spectrum and, therefore, may offer a mix of services and technologies to their customers.

Wireless Centrex

2010-11-12T18:25:00.002-08:00

Centrex—short for “central office exchange”—is a service that handles business calls at the telephone company’s switch rather than through a customer-owned, premisesbased Private Branch Exchange (PBX). Centrex provides a full complement of station features, remote switching, and network interfaces that provides an economical alternative to owning a PBX.

Centrex offers remote options for businesses with multiple locations, providing features that appear to users and the outside world as if the remote sites and the host switch are one system. Centrex-capable switches now support wireless links, which extends the boundaries of business services. Centrex users have access to direct inward dialing (DID) features, as well as station identification on outgoing calls.

Each station has a unique line appearance in the central office, in a manner similar to residential telecommunications subscriber connections. ACentrex call to an outside line exits the switch in the same manner as a toll call exits a local exchange. Users dial a four- or five-digit number without a prefix to call internal extensions and dial a prefix (usually 9) to access outside numbers.

The telephone company operates, administers, and maintains all Centrex switching equipment for the customers. It also supplies the necessary operating power for the switching equipment, including backup power to ensure uninterrupted service during commercial power failures. Centrex may be offered under different brand names. BellSouth calls it Essex, and SBC Communications calls it Plexar, while Verizon calls it CentraNet.

Centrex is also offered through resellers that buy Centrex lines in bulk from the local exchange carrier. Using its own or commercially purchased software, the reseller packages an offering of Centrex and perhaps other basic and enhanced telecommunications services to meet the needs of a particular business. The customer gets a single bill for all local, long-distance, 800, 900, and calling-card services at a fee that is less than the customer would otherwise pay.

Centrex Features

Centrex service offerings typically include direct inward dialing (DID), direct outward dialing (DOD), and automatic identification of outward dialed calls (AIOD). Advanced digital Centrex service provides all the basic and enhanced features of the latest PBXs in the areas of voice communications, data communications, networking, and Integrated Services Digital Network (ISDN) access.

Commonly available features include voice mail, electronic mail, message center support, and modem pooling. For large networks, the Centrex switch can act as a tandem switch, linking a company’s PBXs through an electronic tandem network. Centrex is also compatible with most private switched network applications, including the Federal Telecommunications System (FTS) and the Defense Switched Network (DSN).

Many organizations subscribe to Centrex service primarily because of its networking capabilities, particularly for setting up a virtual citywide network without major cost or management concerns. With city-wide Centrex, a business can set up a network of business locations with a uniform dialing plan, a single published telephone number, centralized attendant service, and full feature transparency for only an incremental cost per month over what a single Centrex site would cost.

Wireless Service

A number of value-added services are available through wireless Centrex. Pacific Bell’s Wireless Centrex, for example, combines an existing Centrex service with Ericsson’s Freeset Business Wireless Telephone system to create a private wireless environment at a company’s business location without incurring expensive cellular airtime charges. At the corporate facility multiple, overlapping cells cover assigned areas.

The number of cells required is determined by traffic density at a given location. An on-premises system called the “radio exchange” handles such functions as powering, control, and facilities for connection to Centrex. Base stations relay calls from the radio exchange to the portable telephones. Each base station provides multiple simultaneous speech channels. The coverage of each base station depends on the character of the environment, but it is typically between 8000 and 15,000 square feet.

Portable telephones contain the intelligence needed to accommodate roaming and cell-to-cell handover. When the radio exchange receives an incoming call, it transmits the identification signal of a portable telephone to all base stations. Because the portable telephone communicates with the nearest base station, even in standby mode, it receives the signal and starts ringing.

When the call is answered, the portable telephone selects the channel with the best quality transmission. Pacific Bell’s Wireless Centrex service gives business users full wireless mobility plus the following options:

Account codes
Authorization codes
Automatic callback
Automatic recall
Call diversion/call forwarding
Call diversion override
Call hold
Call transfer
Call waiting
Call pickup
Speed calling
Call park
Conference/three-way calling
Remote access to network services
Distinctive/priority ringing
Do not disturb
External call forwarding
Executive intrusion/executive busy override
Individual abbreviated dialing/single digit dialing
Speed dialing
Last number redial
Loudspeaker paging
Message waiting indication
Remote access to subscriber features
Select call forwarding

Centrex offers high-quality, dependable, feature-rich telephone service that supports a variety of applications. For many organizations, Centrex offers distinct advantages over on-premises PBX or key/hybrid systems. Centrex can save money over the short term because there is no outlay of cash for an on-premises system. If the service is leased on a month-to-month basis, there is little commitment and no penalty for discontinuing the service.

A company can pick up and move without worrying about reinstalling the system, which may not be right for the new location. With wireless capabilities, businesses get the advantage of mobility without the expense of investing in wireless infrastructure of their own.

Wireless Application Service Providers

2010-11-12T18:25:00.000-08:00

Application service providers (ASPs) host business-class applications in their data centers and make them available to customers on a subscription basis over the network.1 Among the business functions commonly outsourced in this way are customer relationship management (CRM), financial management, human resources, procurement, and enterprise resource planning (ERP).

The ASP owns the applications, and subscribers are charged a fixed monthly fee for use of the applications over secure network connections. Wireless ASPs (WASPs) provide hosted wireless applications so that companies will not have to build their own sophisticated wireless infrastructures.

An ASP enables customers to avoid many of the significant and unpredictable ongoing application management challenges and costs. Following the implementation of software applications, performed for a fixed fee or on a time and materials basis, customers pay a monthly service fee based largely on the number of applications used, total users, the level of service required, and other factors.

By providing application implementation, integration, management, and various upgrade services and related hardware and network infrastructure, the ASP reduces information technology (IT) burdens of its customers, enabling them to focus on their core businesses and react quickly to dynamic market conditions. Traditionally, organizations have installed, operated, and maintained enterprise software applications internally.

The implementation of enterprise software applications often takes twice as long as planned. Moreover, the ongoing costs of operating these applications, including patching, upgrading, training, and management expenses, are often significant, unpredictable, and inconsistent and may increase over time.

The emergence of the Internet, the increased communications bandwidth, and the rewriting of enterprise software to be delivered over IP networks are transforming the way enterprise software applications are being provided to companies. Instead of in-house installations, these applications are beginning to be hosted by third parties, in which the hosting company maintains the applications on an off-site server, typically in a data center, and delivers the applications to customers over the Internet as a service.

In addition, competitive pressures have led to a renewed focus on core competencies, with many businesses concluding that building and maintaining IT capabilities across their entire set of applications are not core competencies. In response to these factors, companies are adopting hosted applications rather than managing them in-house. An ASP typically can complete a standard implementation of its services in 2 to 14 weeks.

This allows customers to avoid the longer implementation times frequently experienced with installing and integrating customized, sophisticated applications. This enables customers to achieve the desired benefits quickly by reducing the time required to establish or augment IT capabilities with wire or wireless infrastructures of their own.

To address this market, many types of companies are setting themselves up as ASPs in this relatively new market, including long-distance carriers, telephone companies, computer firms, Internet service providers (ISPs), software vendors, integrators, and business management consultants. Intel Corp., for example, has built data centers around the world to be ready to host electronic business sites for millions of businesses that will embrace the Internet within 5 years.

Another ASP, Corio, enables businesses to obtain best-ofbreed applications at an affordable cost. Corio is responsible for maintaining and managing the applications and ensuring their availability to its customers from its data centers. For a fixed monthly fee for the suite of integrated business applications and services, businesses can achieve a 70 percent reduction on average of total cost of ownership (TCO) in the first year versus traditional models and a 30 to 50 percent TCO reduction over a 5-year period.

Among the WASPs are Etrieve and Wireless Knowledge. Etrieve combines the reach of wireless, information processing technology, and voice recognition to provide mobile professionals with the right information, at the right time, in the right format. As an extension of the desktop, Etrieve enables mobile professionals to manage their critical office information—e-mail, calendar, and address book—by voice, by text, and by importance. Wireless Knowledge, a subsidiary of Qualcomm, provides mobile access to Microsoft Exchange or Lotus Domino groupware.

Past Attempts

Application outsourcing has been around for nearly 30 years under the concept of the service bureau. In the service bureau arrangement, business users rented applications running the gamut from rudimentary data processing to high-end proprietary payroll. Companies such as EDS and IBM hosted the applications at centralized sites for a monthly fee and typically provided access via low-speed private-line connections.

In an early 1990s incarnation of the service-bureau model, AT&T rolled out hosted Lotus Notes and Novell NetWare services, complete with 24 × 7 monitoring and management. Users typically accessed the applications over a Frame Relay service or dedicated private lines. AT&T’s Notes hosting effort failed and was discontinued in early 1996. The carrier lacked the expertise needed to provide application-focused services and did not offer broad enough access to these applications.

The lesson: Large telecommunications companies are focused on building networks, which is quite different from implementing and managing enterprise applications. In 1998, there emerged renewed interest in this type of service with a new twist—that of providing an array of standardized services to numerous business customers. Economies of scale could be achieved in this “one to many” model by cost reductions incurred in service delivery; specifically by relying on managed IP networks.

Further cost reductions could be achieved by developing implementation templates, innovative application management tools, and integration models that can be used for numerous applications across a variety of companies and industries. To help sell the benefits of applications outsourcing, 25 companies have formed the Applications Service Provider Industry Consortium.

The consortium includes a wide range of companies, including AT&T on the service-provider side. Compaq Computer, IBM, and Sun Microsystems are representative of the systems and software vendors. Interconnect companies such as Cisco Systems are also members. The consortium’s goals include education, common definitions, research, standards, and best practices.

Several trends have come together to rekindle the market for applications outsourcing. The rise of the Internet as an essential business tool, the increasing complexity of enterprise software programs, and the shortage of IT expertise have created a ready environment for carriers and other companies entering the applications hosting business.

The economics of outsourcing are compelling, and new companies are being created to deal with customers’ emerging outsourcing requirements. As wireless technologies become popular, WASPs have emerged to bring applications to mobile devices, saving companies the trouble and expense of doing it themselves.

Wireless Application Protocol

2010-11-12T18:24:00.001-08:00

The Wireless Application Protocol (WAP) is a specification developed by the WAP Forum for sending and reading Internet content and messages on small wireless devices, such as cellular phones equipped with text displays. Common WAP-enabled information services are news, stock quotes, weather reports, flight schedules, and corporate announcements.

Special Web pages called “WAP portals” are specifically formatted to offer information and services. CNN and Reuters are among the content providers that offer news for delivery to cell phones, wireless personal digital assistants (PDAs), and handheld computers. Electronic commerce and e-mail are among the WAP-enabled services that can be accessed from these devices as well.

Typically, these devices will have very small screens, so content must be delivered in a “no frills” format. In addition, the bandwidth constraints of today’s cellular services mean that the content must be optimized for delivery to handheld devices. To get the information in this form, Web sites are built with a light version of the HyperText Markup Language (HTML) called the Wireless Markup Language (WML).

The strength of WAP is that it spans multiple air link standards and, in the true Internet tradition, allows content publishers and application developers to be unconcerned about the specific delivery mechanism. Like the Internet, the WAP architecture is defined primarily in terms of network protocols, content formats, and shared services. This approach leads to a flexible client-server architecture that can be implemented in a variety of ways but which also provides interoperability and portability at the network interfaces.

WAP solves the problem of using Internet standards such as HTML, HyperText Transfer Protocol (HTTP), TLS, and Transmission Control Protocol (TCP) over mobile networks. These protocols are inefficient, requiring large amounts of mainly text-based data to be sent. Web content written with HTML generally cannot be displayed in an effective way on the small-sized screens of pocket-sized mobile phones and pagers, and navigation around and between screens is not easy with one hand.

Furthermore, HTTP and TCP are not optimized for the intermittent coverage, long latencies, and limited bandwidth associated with wireless networks. HTTP sends its headers and commands in an inefficient text format instead of compressed binary format. Wireless services using these protocols are often slow, costly, and difficult to use. The TLS security standard, too, is problematic, since many messages need to be exchanged between client and server.

With wireless transmission latencies, this back-and-forth traffic flow results in a very slow response for the user. WAP has been optimized to solve all these problems. It makes use of binary transmission for greater compression of data and is optimized for long latency and low to medium bandwidth.

WAP sessions cope with intermittent coverage and can operate over a wide variety of wireless transports using the Internet Protocol (IP) where possible and other optimized protocols where IP is impossible. The WML used for WAP content makes optimal use of small screens, allows easy navigation with one hand without a full keyboard, and has built-in scalability from two-line text displays through to the full graphic screens on smart phones and communicators.

WAP Applications Environment

WAP applications are built within the Wireless Application Environment (WAE), which closely follows the Web content delivery model, but with the addition of gateway functions. Figure W-2 contrasts the conventional Web model with the WAE model. All content is specified in formats that are similar to the standard Internet formats and is transported using standard protocols on the Web while using an optimized HTTP-like protocol in the wireless domain (i.e., WAP).

The architecture is designed for the memory and CPU processing constraints that are found in mobile terminals. Support for low-bandwidth and high-latency networks is also included in the architecture as well. Where existing standards were not appropriate due to the unique requirements of small wireless devices, WAE has modified the standards without losing the benefits of Internet technology.

The major elements of the WAE model include:

WAE user agents These client-side software components provide specific functionality to the end user. An example of a user agent is a browser that displays content downloaded from the Web. In this case, the user agent interprets network content referenced by a Uniform Resource Locator (URL). WAE includes user agents for the two primary standard content types: encoded WML and compiled WML Script.

Content generators Applications or services on servers may take the form of Common Gateway Interface (CGI) scripts that produce standard content formats in response to requests from user agents in the mobile terminal. WAE does not specify any particular content generator, since many more are expected to become available in the future.

Standard content encoding A well-defined content encoding, allowing a WAE user agent (e.g., a browser) to conveniently navigate Web content. Standard content encoding includes compressed encoding for WML, bytecode encoding for WMLScript, standard image formats, a multipart container format, and adopted business and calendar data formats (i.e., vCard and vCalendar).

Wireless Telephony Application (WTA) This collection of telephony specific extensions provides call and feature control mechanisms, allowing users to access and interact with mobile telephones for phonebooks and calendar applications.

WMLScript is a lightweight procedural scripting language based on JavaScript. It enhances the standard browsing and presentation facilities of WMLwith behavioral capabilities. For example, an application programmer can use WMLScript to check the validity of user input before it is sent to the network server, provide users with access to device facilities and peripherals, and interact with the user without a round-trip to the network server (e.g., display an error message).

WAP 2.0

The latest version of the Wireless Application Protocol is WAP 2.0, which continues the convergence of WAP with the evolving Internet, merging the work of the WAP Forum, the World Wide Web Consortium (W3C), and the Internet Engineering Task Force (IETF) and enabling more rapid development of new mobile Internet applications.

New technologies of WAP 2.0 that will improve the user experience are data synchronization, multimedia messaging service (MMS), persistent storage interface, provisioning, and pictograms. Additionally, WTA, Push, and User Agent Profile (UAPROF) use more advanced features in WAP 2.0 than in previous versions.

Data synchronization adopts the SyncML protocol to ensure a common solution framework with a multitude of devices. The SyncML messages are supported over both the Wireless Session Protocol (WSP) and the HTTP/1.1 protocols.

Multimedia messaging service provides the framework to develop applications that support feature-rich messaging solutions, permitting delivery of varied types of content in order to tailor the user experience.

Persistent storage interface provides a set of storage services that allows the user to organize, access, store, and retrieve data on wireless devices.

Provisioning permits the network operator to manage the devices on its network with a common set of tools.

Pictogram permits the use of a set of tiny images, allowing users to quickly convey concepts in a small amount of space while transcending traditional language boundaries.

Wireless Telephony Application provides a range of advanced telephony services within the application environment, enabling a host of call handling functions such as making and answering calls, placing them on hold, and redirecting them even while performing data-centric tasks. The availability of these services enables operators to offer customers a unique user interface to control complex network features, such as call forwarding options.

Push technology allows trusted application servers to proactively send personalized content to the end user, such as a sales offer for a product a person might be interested in buying, a new e-mail notification, or a locationdependent promotion. Push technology complements the traditional “pull” model of the Internet, where users request specific information from a Web site.

User agent profile enables application servers to send the appropriate content to the user and to recognize the capabilities of devices, such as screen size and color, to maximize performance potential, bringing the user increased satisfaction.

WAP 2.0 is a next-generation specification that addresses the needs of all players in the wireless industry who plan on incorporating the platform-agnostic specification in their products and services to grow the wireless market by offering value-added features.

WAP is an open global specification that empowers mobile users with wireless devices to easily access and interact with information and services instantly. It is designed to work with most wireless networks, including Bluetooth, Infrared, CDPD, CDMA, GSM, PDC, PHS, TDMA, iDEN, DECT, and GRPS. It can be built to run on any operating system, including PalmOS, EPOC, Windows CE, FLEXOS, OS/9, and JavaOS. WAP offers the additional advantage of providing service interoperability between different device families.

Wireless 911

2010-11-12T18:23:00.001-08:00

The number 911 is the designated universal emergency number in North America for both wireline and wireless telephone service. Dialing 911 puts the caller in immediate contact with a public safety answering point (PSAP) operator who arranges for the dispatch of appropriate emergency services—ambulance, fire, police, rescue—based on the nature of the reported problem.

Since its inception in 1968, this concept has amply demonstrated its value by saving countless lives in thousands of cities and towns across the United States and Canada. In a series of orders since 1996, the Federal Communications Commission (FCC) has taken action to improve the quality and reliability of 911 emergency services for wireless phone users by adopting rules to govern the availability of basic 911 services and the implementation of enhanced 911 (E911) for wireless services.

To further these goals, the agency has required wireless carriers to implement E911 service, subject to certain conditions and schedules. The wireless 911 rules apply to all cellular, broadband Personal Communications Service (PCS) and certain Specialized Mobile Radio (SMR) service providers. These carriers are required to provide to the PSAP the telephone number of the originator of a 911 call and the location of the cell site or base station receiving a 911 call.

This information assists in the provision of timely emergency responses both by providing some information about the general location from which the call is being received and by permitting emergency call takers to reestablish a connection with the caller if the call is disconnected.

All mobile phones manufactured for sale in the United States after February 13, 2000, that are capable of operating in an analog mode, including dual-mode and multimode handsets, must include a special method for processing 911 calls. When a 911 call is made, the handset must override any programming that determines the handling of ordinary calls and must permit the call to be handled by any available carrier, regardless of whether the carrier is the customer’s preferred service provider.

As of October 2001, wireless carriers were required to begin providing automatic location identification (ALI) as part of E911 service implementation, according to the following schedule:

Begin selling and activating ALI-capable handsets no later than October 1, 2001.
Ensure that at least 25 percent of all new handsets activated are ALI-capable no later than December 31, 2001.
Ensure that at least 50 percent of all new handsets activated are ALI-capable no later than June 30, 2002.
Ensure that 100 percent of all new digital handset activated are ALI-capable no later than December 31, 2002 and thereafter.
By December 31, 2005, achieve 95 percent penetration of ALI-capable handsets among its subscribers.

Originally, the FCC envisioned that carriers would need to deploy network-based technologies to provide ALI. However, there have been significant advances in location technologies that employ new or upgraded handsets and that are based on the Global Positioning System (GPS). These methods are approved for implementing enhanced 911 services as well.

Emergency 911 services have become valuable tools in rendering prompt and appropriate assistance to people in critical need. Most states have laws that mandate prompt action on all calls received by a PSAP operator. Unfortunately, 911 systems are so taken for granted that many calls are not for emergencies at all, and expensive resources end up being expended needlessly on trivial pursuits.

PSAP operators now receive calls on such matters as garbage collection dates, late mail delivery, a leaky faucet or heater the landlord won’t fix, directions to stores and restaurants, and whether or not to see a lawyer for this or that problem. The 911 systems in some communities have become so bogged down with nonemergency calls that the subject is frequently addressed by public awareness campaigns in the print and broadcast media.

Wired Equivalent Privacy

2010-11-12T18:22:00.001-08:00

Wired Equivalent Privacy (WEP) is the security protocol specified in the IEEE 802.11b Standard for Wireless Fidelity (Wi-Fi) networks. Akey point of vulnerability exists on the wireless link between client devices and access points. Here, WEP provides a level of security and privacy ostensibly comparable to what is expected of a wired local area network (LAN).

Since it was not intended as an end-to-end security solution, however, users must implement additional safeguards to fully protect their information. WEP relies on a secret key that is shared between a mobile station such as a notebook equipped with a wireless Ethernet card and an access point that provides a wired connection to the LAN. The secret key is used to encrypt packets before they are transmitted, and an integrity check is used to ensure that packets are not modified in transit.

The IEEE standard does not discuss how the shared key is established. In practice, most installations use a single key that is shared between all mobile stations and access points. Commercial products offer more sophisticated key management techniques that can be used to help defend against hacker attacks, but products for the residential market generally lack these features because they require a more technical understanding of security concepts.

WEP uses the RC4 encryption algorithm, which is known as a “stream cipher.” Astream cipher operates by expanding a short key into an infinite pseudo-random key stream. The sending device implements the XOR (exclusive or) operation on the key stream with the plaintext to produce ciphertext. The receiving device has a copy of the same key and uses it to generate an identical key stream.

By implementing XOR on the key stream with the ciphertext, the original plaintext is recovered. Researchers from the University of California at Berkeley have found that this mode of operation makes stream ciphers vulnerable to several attacks. If an attacker flips a bit in the ciphertext, then on decryption the corresponding bit in the plaintext will be flipped.

Also, if an eavesdropper intercepts two ciphertexts encrypted with the same key stream, it is possible to obtain the XOR of the two plaintexts. According to the Berkeley researchers, knowledge of this XOR can enable statistical attacks to recover the plaintexts. The statistical attacks become increasingly effective as more ciphertexts using the same key stream become known.

Once one of the plaintexts becomes known, it is a relatively simple matter to recover all of the others. These attack methods work equally well on both 64- and 128-bit versions of WEP. WEP has defenses against both of these attacks. To ensure that a packet has not been modified in transit, it uses an integrity check (IC) field in the packet. To avoid encrypting two ciphertexts with the same key stream, an initialization vector (IV) is used to augment the shared secret key and produce a different RC4 key for each packet.

The IV is also included in the packet. However, the Berkeley researchers contend that both these measures are implemented incorrectly, resulting in poor security. The integrity check field is implemented as a CRC-32 checksum, which is part of the encrypted payload of the packet. However, CRC-32 is linear, which means that it is possible to compute the bit difference of two CRCs based on the bit difference of the messages over which they are taken.

In other words, flipping bit X in the message results in a deterministic set of bits in the CRC that must be flipped to produce a correct checksum on the modified message. Because flipping bits carries through after an RC4 decryption, this allows the attacker to flip arbitrary bits in an encrypted message and correctly adjust the checksum so that the resulting message appears valid.

Vendors that offer business-class products that use WEP for security on wireless links have dealt with these problems by adding features to WEP. Cisco Systems, for example, offers Dynamic WEP Key Management, which allows network administrators to set time increments in which WEP keys are exchanged per user per session. Increasing the frequency in which keys are exchanged helps systems mitigate the possibility of successful attacks.

Although WEP will be refined continually to increase the security of wireless links, even Cisco recognizes that no single security scheme works for all customers. Accordingly, in addition to WEP, Cisco also offers virtual private network (VPN), firewall, and other features to enhance the end-toend security of corporate networks.

WEP seeks to establish a similar level of protection as that offered by the wired network’s physical security measures by encrypting data transmitted over the wireless LAN. Data encryption protects the vulnerable wireless link between clients and access points. Once this measure has been taken, other typical LAN security mechanisms such as password protection, end-to-end encryption, VPNs, client firewall software, and authentication can be put in place to further ensure privacy.

Voice Compression

2010-11-12T18:21:00.001-08:00

Voice compression entails the application of various algorithms to the voice stream to reduce bandwidth requirements while preserving the quality or audibility of the voice transmission. Numerous compression standards for voice have emerged over the years that allow businesses to achieve substantial savings on leased lines with only a modest cost for additional hardware.

Using these standards, the normal 64-kbps voice channel can be reduced to 32, 16, or 8 kbps, or even as little as 6.3 and 5.3 kbps, for sending voice over the Internet or cellular phone networks. As the compression ratio increases, however, voice quality diminishes. In the 1960s, the CCITT standardized the use of Pulse Code Modulation (PCM) as the internationally accepted coding standard (G.711) for toll-quality voice transmission.

Under this standard, a single voice channel requires 64 kbps when transmitted over the telephone network, which is based on Time Division Multiplexing (TDM). The 64-kbps PCM time slot—or payload bit rate—forms the basic building block for today’s public telephone services and equipment, such that 24 time slots or channels of 64 kbps each that can be supported on a T1 line.

Pulse Code Modulation

A voice signal takes the shape of a wave, with the top and the bottom of the wave constituting the signal’s frequency level, or amplitude. The voice is converted into digital form by an encoding technique called Pulse Code Modulation (PCM). Under PCM, voice signals are sampled at the minimum rate of two times the highest voice frequency level of 4000 Hertz (Hz), which equates to 8000 times per second.

The amplitudes of the samples are encoded into binary form using enough bits per sample to maintain a high signal-to-noise ratio. For quality reproduction, the required digital transmission speed for 4-kHz voice signals works out to 8000 samples per second × 8 bits per sample = 64,000 bps (64 kbps). The conversion of analog voice signals to and from digital is performed by a coder-decoder, or codec, which is a key component of D4 channel banks and multiplexers.

The codec translates amplitudes into binary values and performs mu-law quantizing. The mu-law process (North America only) is an encoding-decoding scheme for improving the signal-to-noise ratio. This is similar in concept to Dolby noise reduction, which ensures quality sound reproduction.

Other components in the channel bank or multiplexer interleave the digital signals representing as many as 24 channels to form a 1.544-Mbps bit stream (including 8 kbps for control) suitable for transmission over a T1 line. PCM exhibits high quality, is robust enough for switching through the public network without suffering noticeable degradation, and is simple to implement. But PCM allows for only 24 voice channels over a T1 line. Digital compression techniques can be applied to multiply the number of channels on a T1 line.

Compression Basics

Among the most popular compression methods is Adaptive Differential Pulse Code Modulation (ADPCM), which has been a worldwide standard since 1984. It is used primarily on private T-carrier networks to double the channel capacity of the available bandwidth from 24 to 48 channels, but it can be applied to microwave and satellite links as well.

ADPCM is also used on some cellular networks such as those based on the Personal Handyphone System (PHS) and Personal Air Communications Systems (PACS). Both employ 32-kbps ADPCM waveform encoding, which provides near landline voice quality. ADPCM has demonstrated a high degree of tolerance to the cascading of voice encoders (vocoders), as experienced when a mobile subscriber calls a voice-mail system and the mailbox owner retrieves the message from a mobile phone.

With other mobile technologies, the playback quality is noticeably diminished, but with PHS and PACS, it is very clear. The ADPCM device accepts the 8000-sample-per-second rate of PCM and uses a special algorithm to reduce the 8-bit samples to 4-bit words. These 4-bit words, however, no longer represent sample amplitudes but only the difference between successive samples. This is all that is necessary for a like device at the other end of the line to reconstruct the original amplitudes.

Integral to the ADPCM device is circuitry called the “adaptive predictor” that predicts the value of the next signal based only on the level of the previously sampled signal. Since the human voice does not usually change significantly from one sampling interval to the next, prediction accuracy can be very high. Afeedback loop used by the predictor ensures that voice variations are followed with minimal deviation.

Consequently, the high accuracy of the prediction means that the difference in the predicted and actual signal is very small and can be encoded with only 4 bits rather than the 8 bits used in PCM. In the event that successive samples vary widely, the algorithm adapts by increasing the range represented by the 4 bits. However, this adaptation will decrease the signal-to-noise ratio and reduce the accuracy of voice frequency reproduction.

At the other end of the digital facility is another compression device, in which an identical predictor performs the process in reverse to reinsert the predicted signal and restore the original 8-bit code. By halving the number of bits to accurately encode a voice signal, T1 transmission capacity is doubled from the original 24 channels to 48 channels, providing the user with a 2 for 1 cost savings on monthly charges for leased T1 lines.

It is also possible for ADPCM to compress voice to 16 kbps by encoding voice signals with only 2 bits instead of 4 bits, as discussed above. This 4 to 1 level of compression provides 96 channels on a T1 line without significantly reducing signal quality. Although other compression techniques are available for use on wire and wireless networks, ADPCM offers several advantages.

ADPCM holds up well in the multinode environment, where it may undergo compression and decompression several times before arriving at its final destination. And unlike many other compression methods, ADPCM does not distort the distinguishing characteristics of a person’s voice during transmission.

Variable-Rate

ADPCM Some vendors have designed ADPCM processors that not only compress voice but also accommodate 64-kbps passthrough as well. The use of very compact codes allows several different algorithms to be handled by the same ADPCM processor. The selection of algorithm is controlled in software and is done by the network manager. Variable-rate ADPCM offers several advantages.

Compressed voice is more susceptible to distortion than uncompressed voice—16 kbps more so than 32 kbps. When line conditions deteriorate to the point where voice compression is not possible without seriously disrupting communications, a lesser compression ratio may be invoked to compensate for the distortion. If line conditions do not permit compression even at 32 kbps, 64-kbps pass-through may be invoked to maintain quality voice communication.

Of course, channel availability is greatly reduced, but the ability to communicate with the outside world becomes the overriding concern at this point rather than the number of channels. Variable-rate ADPCM provides opportunities to allocate channel quality according to the needs of different classes of users. For example, all intracompany voice links may operate at 16 kbps, while those used to communicate externally may be configured to operate at 32 kbps.

The number of channels may be increased temporarily by compressing voice to 16 kbps instead of 32 kbps until new facilities can be ordered, installed, and put into service. As new links are added to keep up with the demand for more channels, the other links may be returned to operation at 32 kbps. Variable-rate ADPCM, then, offers much more channel configuration flexibility than products that offer voice compression at only 32 kbps.

Other Compression Techniques

Other compression schemes can be used over T-carrier facilities, such as Continuously Variable Slope Delta (CVSD) modulation and Time Assigned Speech Interpolation (TASI).

CVSD The higher the sampling rate, the smaller is the average difference between amplitudes. At a high enough sampling rate—32,000 times a second in the case of 32- kbps voice—the average difference is small enough to be represented by only 1 bit. This is the concept behind CVSD modulation, where the 1 bit represents the change in the slope of the analog curve.

Successive 1s or 0s indicate that the slope should get steeper and steeper. This technique can result in very good voice quality if the sampling rate is fast enough. Like ADPCM, CVSD will yield 48 voice channels at 32 kbps on a T1 line. But CVSD is more flexible than ADPCM in that it can provide 64 voice channels at 24 kbps or 96 voice channels at 16 kbps. This is so because the single-bit words are sampled at the signaling rate.

Thus, to achieve 64 voice channels, the sampling rate is 24,000 times a second, while 96 voice channels takes only 16,000 samples per second. In reducing the sampling rate to obtain more channels, however, the average difference between amplitudes becomes greater. And since the greater difference between amplitudes is still represented by only 1 bit, there is a noticeable drop in voice quality. Thus the flexibility of CVSD comes at the expense of quality. It is even possible for CVSD to provide 192 voice channels at 8 kbps.

TASI Since people are not normally able to talk and listen simultaneously, network efficiency at best is only 50 percent. And since all human speech contains pauses that constitute wasted time, network efficiency is further reduced by as much as 10 percent, putting maximum network efficiency at only 40 percent.

Statistical voice compression techniques, such as Time Assignment Speech Interpolation (TASI), take advantage of this quiet time by interleaving various other conversation segments together over the same channel. TASI-based systems actually seek out and detect the active speech on any line and assign only active talkers to the T1 facility. Thus TASI makes more efficient utilization of “time” to double T1 capacity.

At the distant end, the TASI system sorts out and reassembles the interwoven conversations on the line to which they were originally intended. The drawback to statistical compression methods is that they have trouble maintaining consistent quality. This is so because such techniques require a high number of channels, at least 100, from which a good statistical probability of usable quiet periods may be gleaned. However, with as few as 72 channels, a channel gain ratio of 1.5 to 1 may be achieved.

If the number of input channels is too few, a condition known as “clipping” may occur, in which speech signals are deformed by the cutting off of initial or final syllables. Arelated problem with statistical compression techniques is freeze-out, which usually occurs when all trunks are in use during periods of heavy traffic.

In such cases, a sudden burst in speech can completely overwhelm the total available bandwidth, resulting in loss of entire strings of syllables. Another liability inherent in statistical compression techniques, even for large T1 users, is that they are not suitable for transmissions having too few quiet periods, such as when facsimile and music on-hold is used. Statistical compression techniques, then, work better in large configurations than in small ones.

Adding lines and equipment is one way that organizations can keep pace with increases in traffic. But even when funds are immediately available for such network upgrades, communications managers must contend with the delays inherent in ordering, installing, and putting new facilities into service.

To accommodate the demand for bandwidth in a timely manner, communications managers can apply an appropriate level of voice compression to obtain more channels out of the available bandwidth. Depending on the compression technique selected, there need not be a noticeable decrease in voice quality.

Voice Cloning

2010-11-12T18:20:00.003-08:00

Voice cloning is a technology that promises human-sounding synthetic speech that can be used to support existing applications and encourage the development of new applications, particularly for use in mobile phone voice mail, announcement messages, and voice-activated features. Although synthesized speech systems go back to 1939, today’s technology offers voice quality that is so realistic that it justifies being called “cloning.”

Voice cloning is based on technology developed by AT&T Labs and has two components. The first is a text-to-speech engine that turns written words into natural-sounding speech. The second includes a library of voices and the ability to custom-develop a voice, perhaps duplicating a celebrity spokesperson. The English-speaking voice, male or female, can be used to read text on a computer, cell phone, or personal digital assistant (PDA).

The technology can even be added to a car’s computer system to recite driving directions, provide city and restaurant guides, and report on the performance of key subsystems. The speech software is so good at reproducing the sounds, inflections, and intonations of a human voice that it can recreate voices and even bring the voices of long-dead celebrities back to life.

The software, which turns printed text into synthesized speech, makes it possible for a company to use recordings of a person’s voice to utter new things that the person never actually said. The software, called Natural Voices, is not flawless—the synthesized speech may contain a few robotic tones and unnatural inflections—but this is the first text-to-speech software to raise the specter of voice cloning, replicating a person’s voice so perfectly that the human ear cannot tell the difference.

The product itself is provided as a text-to-speech server engine and client software development kit (SDK) that is an integrated collection of C++ classes to help developers integrate text to speech into their applications. The SDK includes a sample application that can be used to explore potential uses of the SDK and text-to-speech server. Both the text-to-speech server engine and SDK run on popular computer and development platforms, including Linux, Solaris, and Windows NT and 2000.

An installation package installs the AT&T Labs Natural Voices TTS engine, documentation, tools, class libraries, sample applications, and demo applications onto the target system. AT&T Labs also offers a custom voice product that entails a person going to a studio where staff record 10 to 40 hours of readings.

Texts range from business and news reports to outright babble. The recordings are then chopped into the smallest number of units possible and sorted into databases. When the software processes text, it retrieves the sounds and reassembles them to form new sentences. In the case of long-dead celebrities, archival recordings can be used in the same way.

Applications

Potential customers for the software, which is priced in the thousands of dollars, include telephone call centers, companies that make software that reads digital files aloud, and makers of automated voice devices. Businesses could use the software to:

Create new revenue-generating applications and services for cell phone users.
Improve customer relationships by putting a pleasantsounding voice interface on applications, products, or services.
Realize mobility and “access anywhere/anytime/any device” strategies by making computer-based information accessible by voice.
Facilitate international expansion plans through a wide variety of text-to-speech languages.

Third-party developers can use voice cloning technology to add significant enhancements to existing applications and services, drive new revenue opportunities, and add “stickiness” to applications or services. Voice on an e-commerce Web site, for example, can make content easily accessible to the visually impaired, which would keep them coming back for future purchases.

The software also can be used by publishers of video games and books on tape. In the near future, people will want high-end speech technology that enables them to interact at length with their cell phones and Palm organizers instead of typing entries and squinting at a tiny screen.

Ownership

Issues Voice cloning technology raises ownership issues. For example, who owns the rights to a celebrity’s voice? This and related issues can be addressed in contracts that include voice-licensing clauses. Current technical limitations may alleviate any worries that a person’s voice could be cloned without permission.

Although the technology is not yet good enough to carry out fraud, synthesized voices eventually may be capable of tricking people into thinking that they are getting phone calls from people they know—such as a politician during an election campaign.

Politicians already make use of machines that perfectly mimic their signatures and handwritten postscript messages, making it appear that they are sending personal letters to constituents. In the not too distant future, we can expect voice cloning to add another personal touch to campaigning.

What is unique about voice cloning is the ability to recreate custom voices. AT&T has previously licensed speech technology, such as SpeechWorks, to other companies but contends that the latest version represents a huge technological leap forward. Despite the technical breakthroughs by AT&T Labs, many engineers are skeptical that a completely simulated voice can be indistinguishable from that of a human.

With the pressure on to perfect the technology, however, it is too soon to rule out this possibility. Already industry analysts are predicting that the market for text-to-speech software will reach more than $1 billion in the next 5 years, providing ample incentive to fine-tune the technology.

Universal Mobila Telephone Service

2010-11-12T18:20:00.001-08:00

One of the major new third-generation (3G) mobile systems being developed within the global IMT-2000 framework is the Universal Mobile Telecommunications System (UMTS), which has been standardized by the European Telecommunications Standards Institute (ETSI). UMTS makes use of UMTS Terrestrial Radio Access (UTRA) as the basis for a global terrestrial radio access network.

Europe and Japan are implementing UTRAin the paired bands 1920–1980 MHz and 2110–2170 MHz. Europe also has decided to implement UTRA in the unpaired bands 1900–1920 MHz and 2010–2025 MHz. UMTS combines key elements of Time Division Multiple Access (TDMA)—about 80 percent of today’s digital mobile market is TDMA-based—and Code Division Multiple Access (CDMA) technologies with an integrated satellite component to deliver wideband multimedia capabilities over mobile communications networks.

The transmission rate capability of UTRAwill provide at least 144 kbps for full-mobility applications in all environments, 384 kbps for limited-mobility applications in the macro- and microcellular environments, and 2.048 Mbps for low-mobility applications particularly in the micro- and picocellular environments. The 2.048-Mbps rate also may be available for short-range or packet applications in the macrocellular environment.

Because the UMTS incorporates the best elements of TDMAand CDMA, this 3G system provides a glimpse of how future wireless networks will be deployed and what possible services may be offered within the IMT-2000 family of systems.

UMTS Objectives

UMTS makes possible a wide variety of mobile services ranging from messaging to speech, data and video communications, Internet and intranet access, and high-bit-rate communication up to 2 Mbps. As such, UMTS is expected to take mobile communications well beyond the current range of wireline and wireless telephony, providing a platform that will be ready for implementation and operation in the year 2002.

UMTS is intended to provide globally available, personalized, and high-quality mobile communication services. Its objectives include:

Integration of residential, office, and cellular services into a single system, requiring one user terminal.
Speech and service quality at least comparable to current fixed networks.
Service capability up to multimedia.
Separation of service provisioning and network operation.
Number portability independent of network or service provider.
The capacity and capability to serve over 50 percent of the population.
Seamless and global radio coverage and radio bearer capabilities up to 144 kbps and further to 2 Mbps.
Radio resource flexibility to allow for competition within a frequency band.

Description

UMTS separates the roles of service provider, network operator, subscriber, and user. This separation of roles makes pos sible innovative new services without requiring additional network investment from service providers. Each UMTS user has a unique network-independent identification number, and several users and terminals can be associated with the same subscription, enabling one subscription and bill per household to include all members of the family as users with their own terminals.

This arrangement would give children access to various communications services under their parents’ account. This application also would be attractive for businesses that require cost-efficient system operation— from subscriber/user management down to radio system—as well as adequate subscriber control over the user services. UMTS supports the creation of a flexible service rather than standardizing the implementations of services in detail.

The provision of services is left to service providers and network operators to decide according to the market demand. The subscriber— or the user when authorized by the subscriber— selects services into individual user service profiles, either with the subscription or interactively with the terminal. UMTS supports its services with networking, broadcasting, directory, localization, and other system facilities, giving UMTS a clear competitive edge over mobile speech and restricted data services of earlier-generation networks.

Being adept at providing new services, UMTS is also competitive in the cost of speech services and as a platform for new applications. UMTS offers a high-quality radio connection that is capable of supporting several alternative speech codecs at 2 to 64 kbps, as well as image, video, and data codecs. Also supported are advanced data protocols covering a large portion of those used in Integrated Services Digital Network (ISDN). The concept includes variable and high bit rates up to 2 Mbps.

Functional Model

The UMTS functional model relies on distributed databases and processing, leaving room for service innovations without the need to alter implemented UMTS networks or existing UMTS terminals. This service-oriented model provides three main functions: management and operation of services, mobility and connection control, and network management.

Management and operation of services Aservice data function (SDF) handles storage and access to service-related data. Aservice control function (SCF) contains overall service and mobility control logic and service-related data processing. Aservice switching function (SSF) invokes service logic—to request routing information, for example. Acall control function (CCF) analyzes and processes service requests in addition to establishing, maintaining, and releasing calls.

Mobility and connection control Drawing on the contents of distributed databases, UMTS will provide for the realtime matching of user service profiles to the available network services, radio capabilities, and terminal functions. This function will handle mobile subscriber registration, authentication, location updating, handoffs, and call routing to a roaming subscriber.

Network management Under UMTS, the administration and processing of subscriber data, maintenance of the network, and charging, billing, and traffic statistics will remain within the traditional telecommunications management network (TMN).

TMN consists of a series of interrelated national and international standards and agreements that provide for the surveillance and control of telecommunications service provider networks on a worldwide scale. The result is the ability to achieve higher service quality, reduced costs, and faster product integration. TMN is also applicable in wireless communications, CATV networks, private overlay networks, and other large-scale, high-bandwidth communications networks.

With regard to UTMS (and other 3G wireless networks), TMN will be enhanced to accommodate new requirements. In areas such as service profile management, routing, and radio resource management between UMTS services, networks, and terminal capabilities, new TMN elements will be developed.

Bearer Services

Under UMTS, four kinds of bearer services will be provided to support virtually any current and future application:

Class A This bearer service offers constant-bit-rate (CBR) connections for isochronous (real-time) speech transmission. This service provides a steady supply of bandwidth to ensure the highest quality speech.
Class B This bearer service offers variable-bit-rate connections that are suited for bursty traffic, such as transaction-processing applications.
Class C This bearer service is a connection-oriented packet protocol that can be used support time-sensitive legacy data applications such as those based on IBM’s Systems Network Architecture (SNA).
Class D This is a connectionless packet bearer service. This is suitable for accessing data on the public Internet or private intranets.

By harnessing the best in cellular, terrestrial, and satellite wideband technology, UMTS will guarantee access to all communications, from simple voice telephony to high-speed, high-quality multimedia services. It will deliver information directly to users and provide them with access to new and innovative services and applications.

It will offer mobile personalized communications to the mass market regardless of location, network, or terminal used. Users will be provided with adaptive multimode/multiband phones or terminals with a flexible air interface to enable global roaming across locations and with backward compatibility with second-generation (2G) systems.

Ultra Wideband

2010-11-12T18:19:00.003-08:00

Ultra wideband (UWB) offers the promise of new radar and imaging services that can save lives by helping to rescue hostages, locate disaster victims trapped under the rubble of a collapsed building, detect hidden flaws in the construction of highways or airport runways, secure homes and businesses, and possibly even provide short-range high-speed Internet access to the classroom.

UWB devices operate by employing very narrow or short-duration pulses that result in very large or wideband transmission bandwidths. Its ultrawide disbursement of ultra-low power bursts presents novel interference questions that must be addressed, including how to ensure that existing services are not adversely impacted—especially those services which support public safety—and whether widespread deployment would have any appreciable effect on the noise floor.

With appropriate technical standards, however, UWB devices can operate using spectrum occupied by existing radio services without causing interference, thereby permitting scarce spectrum resources to be used more efficiently. In early 2002, the Federal Communications Commission (FCC) issued standards designed to ensure that existing and planned radio services, particularly safety services, are adequately protected from UWB users.

The FCC will enforce the rules and act quickly on any reports of interference. The standards are based in large measure on standards that the National Telecommunications and Information administration (NTIA) believes are necessary to protect against interference to vital federal government operations. On an ongoing basis, the FCC intends to review the standards for UWB devices, explore more flexible standards, and address the operation of additional types of UWB operations and technology.

Since there is no production UWB equipment available at this writing and there is little operational experience with the impact of UWB on other radio services, the FCC chose to err on the side of conservatism in setting emission limits when there are unresolved interference issues. The FCC establishes different technical standards and operating restrictions for three types of UWB devices based on their potential to cause interference.

These three types of UWB devices are imaging systems, including groundpenetrating radars (GPRs), wall, through-wall, medical imaging, and surveillance devices; vehicular radar systems; and communications and measurement systems.

Imaging systems Provides for the operation of GPRs and other imaging devices subject to certain frequency and power limitations. The operators of imaging devices must be eligible for licensing, except that medical imaging devices may be operated by a licensed health care practitioner. At the request of NTIA, the FCC will notify or coordinate with NTIAprior to the operation of all imaging systems. Imaging systems include:

Ground-penetrating radar systems GPRs must be operated below 960 MHz or in the frequency band 3.1 to 10.6 GHz. GPRs operate only when in contact with or within close proximity of the ground for the purpose of detecting or obtaining the images of buried objects. The energy from the GPR is intentionally directed down into the ground for this purpose. Operation is restricted to law enforcement, fire and rescue organizations, scientific research institutions, commercial mining companies, and construction companies.

Wall-imaging systems Wall-imaging systems must be operated below 960 MHz or in the frequency band 3.1 to 10.6 GHz. Wall-imaging systems are designed to detect the location of objects contained within a “wall,” such as a concrete structure, the side of a bridge, or the wall of a mine. Operation is restricted to law enforcement, fire and rescue organizations, scientific research institutions, commercial mining companies, and construction companies.

Through-wall imaging systems These systems must be operated below 960 MHz or in the frequency band 1.99 to 10.6 GHz. Through-wall imaging systems detect the location or movement of persons or objects that are on the other side of a structure such as a wall. Operation is limited to law enforcement and fire and rescue organizations.

Medical systems These devices must be operated in the frequency band 3.1 to 10.6 GHz. Amedical imaging system may be used for a variety of health applications to “see” inside the body of a person or animal. Operation must be at the direction of or under the supervision of a licensed health care practitioner.

Surveillance systems Although technically these devices are not imaging systems, for regulatory purposes they are treated in the same way as through-wall imaging and are permitted to operate in the frequency band 1.99 to 10.6 GHz. Surveillance systems operate as “security fences” by establishing a stationary radio frequency (RF) perimeter field and detecting the intrusion of persons or objects in that field. Operation is limited to law enforcement, fire and rescue organizations, public utilities, and industrial entities.

Surveillance systems Although technically these devices are not imaging systems, for regulatory purposes they are treated in the same way as through-wall imaging and are permitted to operate in the frequency band 1.99 to 10.6 GHz. Surveillance systems operate as “security fences” by establishing a stationary radio frequency (RF) perimeter field and detecting the intrusion of persons or objects in that field. Operation is limited to law enforcement, fire and rescue organizations, public utilities, and industrial entities.

Communications and measurement systems Provides for use of a wide variety of other UWB devices, such as highspeed home and business networking devices as well as storage tank measurement devices under Part 15 of the FCC’s rules subject to certain frequency and power limitations. The devices must operate in the frequency band 3.1 to 10.6 GHz. The equipment must be designed to ensure that operation can only occur indoors, or it must consist of handheld devices that may be employed for such activities as peer-to-peer operation.

UWB technologies are destined to play a significant public safety role. UWB devices will save the lives of firefighters and police officers, prevent automobile accidents, assist search-and-rescue crews in seeing through the rubble of disaster sites, enable broadband connections between home electronics, and allow new forms of communications in the years ahead. The U.S. government already uses UWB extensively to make soldiers, airport runways, and highway bridges safer.

But opinion differs greatly on the interference effect of the widespread use of UWB technologies by the public. If interference does occur, it conceivably could affect critical government and nongovernment spectrum users. National defense and several safety-of-life systems depend on bands that have the potential to be impacted by UWB devices. For this reason, the FCC and NTIAwill cooperate in managing the use of UWB technology.

Time Division Multiple Access

2010-11-12T18:19:00.001-08:00

Time Division Multiple Access (TDMA) technology is used in digital cellular telephone communication. It divides each cellular channel into three time slots to increase the amount of conversations that can be carried. TDMAimproves the bandwidth utilization and overall system capacity offered by older FM radio systems by dividing the 30-kHz channel into three narrower channels of 10 kHz each. Newer forms of TDMA allow even more users to be supported by the same channel.

TDMA systems have been providing commercial digital cellular service since mid-1992. Versions of the technology are used to provide Digital American Mobile Phone Service (D-AMPS), Global System for Mobile (GSM) communications, Personal Digital Cellular (PDC), and Digital Enhanced Cordless Telecommunications (DECT). Originally, the TDMA specification was described in EIA/TIAInterim Standard 54 (IS-54).

An evolved version of that standard is IS-136, which is used in the United States for both cellular and Personal Communications Services (PCS) in the 850- MHz and 1.9-GHz frequency bands, respectively. The difference is that IS-136 makes use of a control channel to provide advanced call features and messaging services.

Time Slots

As noted, TDMA divides the original 30-kHz channel into three time slots. Users are assigned their own time slot into which voice or data are inserted for transmission via synchronized timed bursts. The bursts are reassembled at the receiving end and appear to provide continuous, smooth communication because the process is very fast.

The digital bit streams that correspond to the three distinct voice conversations are encoded, interleaved, and transmitted using a digital modulation scheme called Differential Quadrature Phase-Shift Keying (DQPSK). Together these manipulations reduce the effects of most common radio transmission impairments. If one side of the conversation is silent, however, the time slot goes unused.

Enhancements to TDMAuse dynamic time slot allocation to avoid the wasted bandwidth when one side of the conversation is silent. This technique almost doubles the bandwidth efficiency of TDMAover the original analog systems. Frequency reuse further enhances network capacity. In nonadjacent cells, the same frequency sets are used as in other cells, but the cells with the same frequency sets are spaced many miles apart to reduce interference.

Framing

In a TDMAsystem, the digitized voice conversations are separated in time, with the bit stream organized into frames, typically on the order of several milliseconds. A6-millisecond frame, for example, is divided into six 1-millisecond time slots, with each time slot assigned to a specific user. Each time slot consists of a header and a packet of user data for the call assigned to it. The header generally contains synchronization and addressing information for the user data.

If the data in the header become corrupted as a result of a transmission problem—signal fade, for example—the entire slot can be wasted, in which case no more data will be transmitted for that call until the next frame. The loss of an entire data packet is called “frame erasure.” If the transmission problem is prolonged (i.e., deep fade), several frames in sequence can be lost, causing clipped speech or forcing the retransmission of data.

Most transmission problems, however, will not be severe enough to cause frame erasure. Instead, only a few bits in the header and user data will become corrupted, a condition referred to as “single-bit errors.”

Network Functions

The IS-54 standard defines the TDMAradio interface between the mobile station and the cell site radio. The radio downlink from the cell site to the mobile phone and the radio uplink from the mobile phone to the cell site are functionally similar. The TDMAcell site radio is responsible for speech coding, channel coding, signaling, modulation/demodulation, channel equalization, signal strength measurement, and communication with the cell site controller.

The TDMAsystem’s speech encoder uses a linear predictive coding technique and transfers Pulse Code Modulated (PCM) speech at 64 kbps to and from the network. The channel coder performs channel encoding and decoding, error correction, and bit interleaving and deinterleaving. It processes speech and signaling information, builds the time slots for the channels, and communicates with the main controller, modulator, and demodulator.

The modulator receives the coded information and signaling bits for each time slot from the channel coders. It performs DQPSK modulation to produce the necessary digital components of the transmitter waveform. These waveform samples are converted from digital to analog signals. The analog signals are then sent to the transceiver, which transmits and receives digitally modulated radiofrequency (RF) control and information signals to and from the cellular phones.

The modulator/equalizer receives signals from the transceiver. It performs filtering, automatic gain control, receive signal strength estimation, adaptive equalization, and demodulation. The demodulated data for each of the time slots is then sent to the channel coder for decoding. Newer voice coding technology is available that produces near-landline speech quality in wireless networks based on the IS-136 TDMAstandard.

One technology uses an algebraic code excited linear predictive (ACELP) algorithm, an enhanced internationally accepted code for dividing waves of sound into binary bits of data. The ACELP coders can be integrated easily into current wireless base station radios as well as new telephones. ACELP-capable phones enable users to take advantage of the improved digital clarity over both North American frequency bands—850 MHz for cellular and 1.9 GHz for PCS.

Call Handoff

Receive signal strength estimation is used in the call handoff process. The traditional handoff process involves the cell site currently serving the call, the switch, and the neighboring cells that potentially can continue the call. The neighboring cells measure the signal strength of the potential call to be handed off and report that measurement to the serving cell, which uses it to determine which neighboring cell can best handle the call.

TDMA systems, on the other hand, reduce the time needed and the overhead required to complete the handoff by assigning some of this signal strength data gathering to the cellular phone, relieving the neighboring cells of this task and reducing the handoff interval.

Digital Control Channel

Digital Control Channel (DCCH), described in IS-136, gives TDMAfeatures that can be added to the existing platform through software updates. Among these new features are:

Over-the-air activation Allows new subscribers to activate cellular or PCS service with just a phone call to the service provider’s customer service center.
Messaging Allows users to receive visual messages up to the maximum length allowed by industry standards (200 alphanumeric characters). Transmission of messages permits a mobile unit to function as a pager.
Sleep mode Extends the battery life of mobile phones and allows subscribers to leave their portables powered on throughout the day, ready to receive calls.
Fraud prevention The cellular system is capable of identifying legitimate mobile phones and blocking access to invalid ones.

A number of other advanced features also can be supported over the DCCH, such as voice encryption and secure data transmission, caller ID, and voice mail notification.

Many vendors and service providers have committed to supporting either TDMAor CDMA. Those who have committed to CDMAclaim that they did so because they consider TDMAto be too limited in meeting the requirements of the next generation of cellular systems. Although TDMA provides service providers with a significant increase in capacity over AMPS, the standard was written to fit into the existing AMPS channel structure for easy migration.

Proponents of TDMA, however, note that the inherent compatibility between AMPS and TDMA, coupled with the deployment of dual-mode/dual-band terminals, offers full mobility to subscribers with seamless handoff between PCS and cellular networks. They also note that the technology is operational in many of the world’s largest wireless networks and is providing reliable, high-quality service without additional development or redesign.

These TDMAsystems can be easily and cost-effectively integrated with existing wireless and landline systems, and the technology is evolving to meet the quality and service requirements of the global third-generation (3G) wireless infrastructure.

Telemetry

2010-11-12T18:18:00.001-08:00

Telemetry is the monitoring and control of remote devices from a central location via wire-line or wireless links. Applications include utility meter reading, load management, environmental monitoring, vending machine management, and security alarm monitoring. Companies are deploying telemetry systems to reduce the cost of manually reading and checking remote devices.

For example, vending machines need not be visited daily to check for proper operation or out-of-stock conditions. Instead, this information can be reported via modem to a central control station so that a repair technician or supply person can be dispatched as appropriate. Such telemetry systems greatly reduce service costs. When telemetry applications use wireless technology, additional benefits accrue.

The use of wireless technology enables systems to be located virtually anywhere without depending on the telephone company for line installation. For instance, a kiosk equipped with a wireless modem can be located anywhere in a shopping mall without incurring line installation costs. Via wireless modems, data are collected from all the area kiosks at the end of the day for batch processing at a data center.

The kiosk also runs continuous diagnostics to ensure proper operation. If a malfunction occurs, problems are reported via the wireless link to a central control facility, which can diagnose and fix the problem remotely or dispatch a technician if necessary.

Security Application

A number of wireless security systems are available for commercial and residential use. Wireless technology provides installation flexibility, since sensors can be placed anywhere without proximity to phone jacks. Anumber of sensors are available to detect such things as temperature, frequency, or motion. The system can be programmed to automatically call monitoring station personnel, police, or designated friends and neighbors when an alert is triggered.

Such systems can be set to randomly turn lights on and off at designated times to give the appearance of occupancy. Depending on vendor, the system may even perform continuous diagnostics to report low battery power or tampering. In a typical implementation, the security system console monitors the sensors placed at various potential points of entry.

The console expects the sensor to send a confirmation signal at preset intervals, say, every 90 seconds. If the console does not get the signal, it knows that something is wrong. For example, a sensor attached to a corner of the window or other glass panel is specially tuned to vibrations caused by breaking glass. When it detects the glass breaking, the sensor opens its contact and sends a wireless signal to an audio alarm located on the premises, at a police station, or at a private security firm.

The use of wireless technology for security applications actually can improve service reliability. Asecurity service that does not require a dedicated phone line is not susceptible to intentional or accidental outages when phone lines are down or there is bad weather. Wireless links offer more immunity to such problems.

Traffic Monitoring

Another common application of wireless technology is its use in traffic monitoring. For example, throughout the traffic signal control industry there has been a serious effort to find a substitute for the underground hard-wired inductive loop that is in common use today to detect the presence of vehicles at stoplights. Although the vehicle detection loop is inherently simple, it has many disadvantages:

Slot cutting for loop and lead-in wire is time-consuming and expensive.
Traffic is disrupted during installation.
Reliability depends on geographic conditions.
Maintenance costs are high, especially in cold climates.

Awireless proximity detector can overcome these problems. Its signals activate traffic lights in the prescribed sequence. The proximity detector, usually mounted on a nearby pole, focuses the wireless signal very narrowly on the road to represent a standard loop. The microprocessor-based detector provides real-time information while screening out such environmental variations as temperature, humidity, and barometric pressure.

By tuning out environmental variations, the detectors provide consistent output. This increases the reliability of traffic control systems. Using a laptop computer with a Windows-compatible setup package, information can be exchanged with the detector via an infrared link. From the laptop, the pole-mounted detector can be set up remotely, calibrated, and put through various diagnostic routines to verify proper operation.

Role of Cellular Carriers

Cellular carriers are well positioned to offer wireless telemetry services. The cellular telephone system has a total of 832 channels, half of which are assigned to each of the two competing cellular carriers in each market. Each cellular carrier uses 21 of its 416 channels as control channels. Each control channel set consists of a Forward Control Channel (FOCC) and a Reverse Control Channel (RECC).

The FOCC is used to send general information from the cellular base station to the cellular telephone. The RECC is used to send information from the cellular telephone to the base station. The control channels are used to initiate a cellular telephone call. Once the call is initiated, the cellular system directs the cellular telephone to a voice channel.

After the cellular telephone has established service on a voice channel, it never goes back to a control channel. All information concerning handoff to other voice channels and termination of the telephone call is handled via communication over the voice channels. This leaves the control channels free to provide other services such as telemetry, which is achieved by connecting a gateway to a port at the local mobile switching center (MSC) or regional facility.

The gateway can process the telemetry messages according to the specific needs of the applications. For instance, if telemetry is used to convey a message from an alarm panel, the gateway will process the message on a real-time, immediate basis and pass the message to the central alarm monitoring service.

On the other hand, if a soft drink vending company uses telemetry to poll its machines at night for their stock status, the gateway will accumulate all the data from the individual vending machines and process them in batch mode so that the management reports can be ready for review the next morning. Individual applications can have different responses from the same telemetry radio.

While the vending machine uses batch processing for its stock status, it could have an alarm message conveyed to the vending company on an immediate basis, indicating a malfunction. Asimilar scenario is applicable for utility meter reading. Normal meter readings can be obtained on a batch basis during the night and delivered to the utility company the following morning.

However, realtime meter readings can be made any time during the day for customers who desire to close out or open service and require an immediate, current meter reading. Telemetry can even be used to turn on or turn off utility service remotely by the customer service representative.

Web-Enabled Telemetry

The next big market for telemetry systems is for those which distribute data through the Internet for access by a Web browser, which lowers the cost of implementing telemetry applications. Agrowing number of companies offer Webenabled telemetry solutions for such applications as ground station telemetry processing as well as remote and wide area monitoring.

With such systems, a host device acts as a network server that plugs into the local area network (LAN) with standard Category 5 cabling and RJ-45 connectors. The host device is connected to remote units over phone lines or wireless links to the Internet. Data are sent and received between the host and remote units in standard Transmission Control Protocol/Internet Protocol (TCP/IP) packets.

Client computers connected anywhere on the LAN or the Internet can use a standard Web browser to display the collected data with no requirement for additional software. In some cases, integrated Java applets provide real-time telemetry display. With accumulated data published as Web pages over an Ethernet LAN or over the Internet, it possible to monitor and control a process through a browser from anywhere in the world.

For example, using a remote unit attached to a heater with a wireless link to an access point, an engineer can monitor the temperature, change set points or alarm points, turn the heater on and off, or make other modifications from anywhere on the local network, or anywhere on the Internet, simply by using a Web browser. The remote unit also can send an e-mail message to the engineer alerting him or her to an alarm condition or updating the status of the remote device.

Leveraging the technology of the Internet even further, the engineer could receive a message from the remote unit on an Internet-capable pager or cell phone. Through the Web browser an administrator can set monitoring and measurement parameters from any computer on the network and configure and change all communication parameters of the remote units in the field. Access to configurations and data is protected through passwords. Selectable local disk archiving protects data for future reference should the primary storage disk fail.

Telemetry services, once implemented by large companies over private networks, are becoming more widely available for a variety of mainstream business and consumer applications. Wireless technology permits more flexibility in the implementation of telemetry systems and can save on line installation costs.

Telemetry systems are inherently more reliable when wireless links are used to convey status and control information, since they are less susceptible to outages due to tampering and severe weather. As data communications technology advances and companies continue to exploit the global ubiquity of the Internet, telemetry solutions will become more pervasive.

Telegraphy

2010-11-12T18:17:00.003-08:00

Telegraphy is a form of data communication that is based on the use of a signal code. The word telegraphy comes from Greek tele meaning “distant” and graphein meaning “to write”—writing at a distance. The inventor of the first electric telegraph was Samuel Finley Breese Morse, an American inventor and painter.

On a trip home from Italy, Morse became acquainted with the many attempts to create usable telegraphs for long-distance telecommunications. He was fascinated by this problem and studied books on physics for 2 years to acquire the necessary scientific knowledge.

Morse focused his research on the characteristics of electromagnets, whereby they became magnets only while the current flows. The intermittence of the current produced two states—magnet and no magnet—from which he developed a code for representing characters, which eventually became known as Morse Code. (The International Morse Code is a system of dots and dashes that can be used to send messages by a flash lamp, telegraph key, or other rhythmic device such as a tapping finger.)

His first attempts at building a telegraph failed, but he eventually succeeded with the help of some friends who were more technically knowledgeable. The signaling device was very simple. It consisted of a transmitter containing a battery and a key, a small buzzer as a receiver, and a pair of wires connecting the two. Later, Morse improved it by adding a second switch and a second buzzer to enable transmission in the opposite direction as well.

In 1837, Morse succeeded in a public demonstration of his first telegraph. Although he received a patent for the device in 1838, he worked for 6 more years in his studio at New York University to perfect his invention. Finally, on May 24,1844, with a $30,000 grant from Congress, Morse unveiled the results of his work. Over a line strung from Washington, D.C., to Baltimore, Morse tapped out the message, “What hath God wrought.”

The message reached Morse’s collaborator, Alfred Lewis Vail, in Baltimore, who immediately sent it back to Morse. With the success of the telegraph assured, the line was expanded to Philadelphia, New York, Boston, and other major cities and towns. The telegraph lines tended to follow the rights-of-way of railroads, and as the railroads expanded westward, the nation’s communications network expanded as well.

Morse Code uses a system of dots and dashes that are tapped out by an operator using a telegraph key. (It also can be used to communicate via radio and flash lamp.) Various combinations of dots and dashes represent characters, numbers, and symbols separated by spaces.

Morse Code is the basis of today’s digital communication. Although it has virtually disappeared in the world of professional communication, it is still used in the world of amateur radio (HAM) and is kept alive by history buffs. There are even pages on the Web that teach telegraphy and perform translations of text into Morse Code.

Wireless Telegraphy

An Italian inventor and electrical engineer, Guglielmo Marconi (1874–1937), pioneered the use of wireless telegraphy. Telegraph signals previously had been sent through electrical wires. In experiments he conducted in 1894, Marconi demonstrated that telegraph signals also could be sent through the air.

A few years earlier, Heinrich Hertz had produced and detected the waves across his laboratory. Marconi’s achievement was in producing and detecting the waves over long distances, laying the groundwork for what today we know as radio. So-called Hertzian waves were produced by sparks in one circuit and detected in another circuit a few meters away.

By continuously refining his techniques, Marconi could soon detect signals over several kilometers, demonstrating that Hertzian waves could be used as a medium for communication. The results of these experiments led Marconi to approach the Italian Ministry of Posts and Telegraphs for permission to set up the first wireless telegraph service. He was unsuccessful, but in 1896, his cousin, Henry Jameson-Davis, arranged an introduction to Nyilliam Preece, engineer-inchief of the British Post Office.

Encouraging demonstrations in London and on Salisbury Plain followed, and in 1897, Marconi obtained a patent and established the Wireless Telegraph and Signal Company, Ltd, which opened the world’s first radio factory at Chelmsford, England, in 1898. Experiments and demonstrations continued. Queen Victoria at Osborne House received bulletins by radio about the health of the Prince of Wales, convalescing on the royal yacht off Cowes.

Radio transmission was pushed to greater and greater lengths, and by 1899, Marconi had sent a signal 9 miles across the Bristol Channel and then 31 miles across the English Channel to France. Most people believed that the curvature of the earth would prevent sending a signal much farther than 200 miles, so when Marconi was able to transmit across the Atlantic in 1901, it opened the door to a rapidly developing wireless industry.

Commercial broadcasting was still in the future—the British Broadcasting Company (BBC) was established in 1922—but Marconi had achieved his aim of turning Hertz’s laboratory demonstration into a practical means of communication.

By Morse’s death in 1872, the telegraph was being used worldwide and would pave the way for the invention of the telephone. Western Union had the monopoly on commercial telegraph service but spurned Alexander Graham Bell, who approached the company with an improvement that would convey voice over the same wires.

Bell had to form his own company, American Bell Telephone Company, to offer a commercial voice communication service. Since then, voice and data technologies have progressed through separate evolutionary paths. Only in recent years has voice-data integration been pursued as a means of containing the cost of telecommunication services.

Spread Spectrum Radio

2010-11-12T18:17:00.001-08:00

Spread spectrum is a digital coding technique in which the signal is taken apart or “spread” so that it sounds more like noise to the casual listener, allowing many more users to share the available bandwidth while affording each conversation a high degree of privacy. Actress Hedy Lamarr (Figure S-5) and composer George Antheil share the patent for spread-spectrum technology.

Their patent for a “Secret Communication System,” issued in 1942, was based on the frequency-hopping concept, with the keys on a piano representing the different frequencies and frequency shifts. Lamarr had become intrigued with radio-controlled missiles and the problem of how easy it was to jam the guidance signal. She realized that if the signal jumped from frequency to frequency quickly—like changing stations on a radio—and both sender and receiver changed in the same order at the same time, then the signal could never be blocked without knowing exactly how and when the frequency changed.

Although the frequency-hopping idea could not be implemented at that time because of technology limitations, it eventually became the basis for cellular communication based on Code Division Multiple Access (CDMA) and wireless Ethernet LANs based on infrared technology.

Frequency Assignment

Spread spectrum uses the industrial, scientific, and medical (ISM) bands of the electromagnetic spectrum. The ISM bands include the frequency ranges at 902 to 928 MHz and 2.4 to 2.484 GHz, which do not require a site license from the FCC. Spread spectrum is a highly robust wireless data transmission technology that offers substantial performance advantages over conventional narrowband radio systems.

As noted, the digital coding technique used in spread spectrum takes the signal apart and spreads it over the available bandwidth, making it appear as random noise. The coding operation increases the number of bits transmitted and expands the bandwidth used. Noise has a flat, uniform spectrum with no coherent peaks and generally can be removed by filtering.

The spread signal has a much lower power density but the same total power. This low power density, spread over the expanded transmitter bandwidth, provides resistance to a variety of conditions that can plague narrowband radio systems, including:

Interference Acondition in which a transmission is being disrupted by external sources, such as the noise emitted by various electromechanical devices, or internal sources such as cross-talk.
Jamming Acondition in which a stronger signal overwhelms a weaker signal, causing a disruption to data communications.
Multipath Acondition in which the original signal is distorted after being reflected off a solid object.
Interception Acondition in which unauthorized users capture signals in an attempt to determine its content.

Non-spread-spectrum narrowband radio systems transmit and receive on a specific frequency that is just wide enough to pass the information, whether voice or data. In assigning users different channel frequencies, confining the signals to specified bandwidth limits, and restricting the power that can be used to modulate the signals, undesirable cross-talk—interference between different users—can be avoided.

These rules are necessary because any increase in the modulation rate widens the radio signal bandwidth, which increases the chance for cross-talk. The main advantage of spread-spectrum radio waves is that the signals can be manipulated to propagate fairly well through the air, despite electromagnetic interference, to virtually eliminate cross-talk.

In spread-spectrum modulation, a signal’s power is spread over a larger band of frequencies. This results in a more robust signal that is less susceptible to interference from similar radio-based systems, since, although they too are spreading their signals, they use different spreading algorithms.

Spreading

Spread spectrum is a digital coding technique in which a narrowband signal is taken apart and “spread” over a spectrum of frequencies (Figure S-6). The coding operation increases the number of bits transmitted and expands the amount of bandwidth used. With the signal’s power spread over a larger band of frequencies, the result is a more robust signal that is less susceptible to impairment from electromechanical noise and other sources of interference.

It also makes voice and data communications more secure. Using the same spreading code as the transmitter, the receiver correlates and collapses the spread signal back down to its original form. The result is a highly robust wireless data transmission technology that offers substantial performance advantages over conventional narrowband radio systems. There are two spreading techniques in common use today: direct sequence and frequency hopping.

Direct Sequence In direct sequence spreading—the most common implementation of spread-spectrum technology—the radio energy is spread across a larger portion of the band than is actually necessary for the data. Each data bit is broken into multiple subbits called “chips.” The higher modulation rate is achieved by multiplying the digital signal with a chip sequence. If the chip sequence is 10, for example, and it is applied to a signal carrying data at 300 kbps, then the resulting bandwidth will be 10 times wider.

The amount of spreading depends on the ratio of chips to each bit of information. Because data modulation widens the radio carrier to increasingly larger bandwidths as the data rate increases, this chip rate of 10 times the data rate spreads the radio carrier to 10 times wider than it would otherwise be for data alone. The rationale behind this technique is that a spreadspectrum signal with a unique spread code cannot create the exact spectral characteristics as another spread-coded signal.

Using the same code as the transmitter, the receiver can correlate and collapse the spread signal back down to its original form, while other receivers using different codes cannot. This feature of spread spectrum makes it possible to build and operate multiple networks in the same location. When each network is assigned its own unique spreading code, all transmissions can use the same frequency range yet remain independent of each other.

The transmissions of one network appear to the other as random noise and are filtered out because the spreading codes do not match. This spreading technique would appear to result in a weaker signal-to-noise ratio, since the spreading process lowers the signal power at any one frequency. Normally, a low signal-to-noise ratio would result in damaged data packets that would require retransmission.

However, the processing gain of the despreading correlator recovers the loss in power when the signal is collapsed back down to the original data bandwidth but is not strengthened beyond what would have been received had the signal not been spread. The FCC has set rules for direct sequence transmitters.

Each signal must have 10 or more chips. This rule limits the practical raw data throughput of transmitters to 2 Mbps in the 902-MHz band and 8 Mbps in the 2.4-GHz band. The number of chips is directly related to a signal’s immunity to interference. In an area with a lot of radio interference, users will have to give up throughput to successfully limit interference.

Frequency Hopping In frequency hopping, the transmitter jumps from one frequency to the next at a specific hopping rate in accordance with a pseudo-random code sequence. The order of frequencies selected by the transmitter is taken from a predetermined set as dictated by the code sequence. For example, the transmitter may have a hopping pattern of going from Channel 3 to Channel 12 to Channel 6 to Channel 11 to Channel 5, and so on.

The receiver tracks these changes. Since only the intended receiver is aware of the transmitter’s hopping pattern, then only that receiver can make sense of the data being transmitted. Other frequency-hopping transmitters will be using different hopping patterns that usually will be on noninterfering frequencies. Should different transmitters coincidentally attempt to use the same frequency and the data of one or both become garbled at that point, retransmission of the affected data packets is required.

Those data packets will be sent again on the next hopping frequency of each transmitter. The FCC mandates that frequency-hopped systems must not spend more than 0.4 second on any one channel each 20 seconds, or 30 seconds in the 2.4-GHz band. Furthermore, they must hop through at least 50 channels in the 900-MHz band or 75 channels in the 2.4-GHz band. These rules reduce the chance of repeated packet collisions in areas with multiple transmitters.

Direct sequence spread spectrum offers better performance, but frequency-hopping spread spectrum is more resistant to interference and is preferable in environments with electromechanical noise and more stringent security requirements. Direct sequence is more expensive than frequency hopping and uses more power.

Although spread spectrum generally provides more secure data transmission than conventional narrowband radio systems, this does not mean the transmissions are immune from interception and decoding by knowledgeable intruders with sophisticated tapping equipment. For this reason, many vendors provide optional encryption for added security.

Spectrum Planning

2010-11-12T18:16:00.001-08:00

Radio spectrum is managed as a scarce natural resource in the United States. It is scarce because at any given time and place one use of a portion of the spectrum precludes any other use of that portion. In the broadcasting service alone, the broadcaster must know where the station’s signal can be received in order to meet the needs of advertisers.

Interference is unacceptable because it unnaturally limits the broadcaster’s market. Similarly, a taxi company or a police department must be able to reliably determine their coverage areas and know that they will be able to operate without interference in that area. Consequently, for the public good, the use of the radio spectrum is regulated, access is controlled, and rules for its implementation are enforced because of the possibility for interference between uncoordinated uses.

Spectrum planning in the United States is the shared responsibility of the National Telecommunications and Information Administration (NTIA) and the Federal Communications Commission (FCC). The NTIAis an agency within the U.S. Department of Commerce and is responsible for ensuring the spectrum requirements of federal government users.

The FCC is an independent regulatory agency headed by five members who are appointed for 5-year terms by the President, with the advice and consent of the Senate. It is responsible for ensuring the spectrum needs of commercial operators and that the public interest is served by a competitive environment. Both the NTIAand the FCC work with other executive branch agencies to allocate portions of the spectrum for specific radio services.

Any spectrum shared by federal and nonfederal users is jointly managed by the NTIAand the FCC. Because 93.1 percent of the spectrum below 30 GHz is shared, with only 5.5 and 1.4 percent allocated, respectively, to the private sector and the government on exclusive bases, effective coordination between the NTIAand the FCC is essential.

The NTIA and the FCC establish their individual spectrum requirements and then coordinate these requirements with one another through the Interdepartment Radio Advisory Committee (IRAC). If difficulties arise in the coordination process, the IRAC typically facilitates the negotiation efforts. The current approach to wireless spectrum allocation is viewed by experts as seriously fractured and in need of revision, given the rapid evolution of technology.

While progress has been made in the FCC’s methods of assigning spectrum, primarily through auctions, allocation policy has not kept pace with the increasing demand, with the result that the allocation system is not moving spectrum to its best uses in a timely manner. To assist it in identifying and evaluating changes in spectrum policy that will increase the public benefits derived from the use of the radio spectrum, the FCC has established a Spectrum Policy Task Force.

The responsibilities of the task force are to provide specific recommendations to the FCC for ways in which to evolve the current “command and control” approach to spectrum policy into a more integrated, market-oriented approach that provides greater regulatory certainty while minimizing regulatory intervention.

The task force also assists the FCC in addressing ubiquitous spectrum issues, including interference protection, spectral efficiency, effective public safety communications, and implications of international spectrum policies. Congress also can influence spectrum allocations through legislation. Once spectrum is allocated, the frequencies become available for managed federal use under the authority of NTIAand for state and local government and commercial use under the authority of the FCC.

Federal courts also have something to say about spectrum matters—specifically about FCC enforcement. For example, NextWave Telecom, a small wireless carrier embroiled in bankruptcy, won back the rights to airwave licenses worth billions of dollars when a U.S. Appeals Court ruled in mid- 2001 that the FCC had stripped the company’s spectrum improperly when it defaulted on its payments.

The 90 licenses at issue, which NextWave picked up in a 1996 spectrum auction for more than $4.7 billion, provide as much as 30 MHz in major cities. Ultimately, NextWave sold the licenses to AT&T, Cingular, Verizon, and VoiceStream for $16 billion, with NextWave getting $5 billion and the U.S. Treasury getting $11 billion. International spectrum allocations typically influence allocation decisions within the United States; however, the interests of the federal government and commercial spectrum users usually take precedence.

Therefore, domestic and international spectrum allocations do not always coincide, as in the case of third-generation (3G) networks, which use different frequency bands—one set for the United States and a different set for the rest of the world.

Radio spectrum is managed as a scarce natural resource. It is scarce because at any given time and place one use of a portion of the spectrum precludes any other use of that portion. In the broadcasting service alone, the broadcaster must know where the station’s signal can be received in order to meet the needs of advertisers. Interference is unacceptable because it unnaturally limits the broadcaster’s market.

Similarly, a taxi company or a police department must be able to reliably determine its coverage area and know that it will be able to operate without interference in that area. Consequently, for the public good, the use of the radio spectrum is regulated, access is controlled, and rules for its use are enforced because of the possibility for interference between uncoordinated uses.

Spectrum Auctions

2010-11-12T18:15:00.003-08:00

In recent years, the FCC has assigned licenses for wireless spectrum by putting it up for auction. The idea behind the auction process is that is encourages companies to roll out new services as soon as possible to recover their investments in the licenses. In getting spectrum into the hands of those who initially value it the most, competitive bidding also facilitates efficient spectrum aggregation rather than fragmented secondary markets.

In the past, the FCC often relied on comparative hearings, in which the qualifications of competing applicants were examined to award licenses in cases where two or more applicants filed applications for the same spectrum in the same market. This process was time-consuming and resource-intensive. The FCC also used lotteries to award licenses, but this created an incentive for companies to acquire licenses on a speculative basis and resell them.

Of the three methods of assigning spectrum, competitive bidding has proved to be the most effective way to ensure that licenses are assigned quickly and to the companies that value them the most while recovering the value of the spectrum resource for the public.1 In addition, auctions avoid the perception of the government making decisions that are biased toward or against individual industry players. The rules and procedures of the auctions are clearly established, and the outcomes are definitive.

Auction Process

The FCC’s auctions of electromagnetic spectrum assign licenses using a unique methodology called “electronic simultaneous multiple-round auctions.” This methodology is similar to a traditional auction, except that instead of licenses being sold one at a time, a large set of related licenses is auctioned simultaneously and bidders can bid on any license offered.

The auction closes when all bidding activity has stopped on all licenses. Another characteristic of the auction process is that it is automated. When the FCC began to design auctions for the airwaves, it became apparent that manual auction methods could not adequately allocate large numbers of licenses when thousands of interdependent licenses were being auctioned to hundreds of bidders at the same time.

The FCC’s Automated Auction System (AAS) provides the necessary tools to conduct large auctions very efficiently. The system accommodates the needs of bidders by allowing them to bid from their offices using a PC and a modem through a private and secure wide area network (WAN). The system also can accommodate on-site bidders and telephonic bidding.

Bidders and other interested parties are able to track the progress of the auctions through the Auction Tracking Tool (ATT), a stand-alone application that allows a user to track detailed information on an auction. During an auction, the FCC releases result files after every round, with details on all the activity that occurred in that round. Users can use the ATT to import these round result files into a master database file and then view a number of different tables containing a large amount of data in a spreadsheet view.

Users can sort, filter, and query the tables to track the activity of an auction in virtually any way they desire. There are also canned tables containing simple summary data to allow more casual observers to track the progress of the auction in general. The FCC also provides the capability to plot maps of auction winners, high bidders by round, and more general auction activity.

Through a Geographic Information System (GIS), interested parties can use a Web browser–based application to construct queries against the database for a particular auction and have the results displayed in a map format. The GIS presents its query results primarily in maps, which the user can export to easily transportable graphical formats. The GIS also allows the user to display data in tabular format.

Currently, there are three queries that can be executed against any closed or open auction in the GIS:

Market analysis by number of bids Allows users to see which licenses received a bid in a given round and how many bids each market received.
Round results summary Provides a high-level summary of activity for the selected round, depicting markers for which a new high bid was received, markets for which a bid was withdrawn, and markets that had no new activity.
Bidder activity Allows users to query the database to generate a map showing all the licenses for which a particular area has a high bid in a given round.

Companies interested in participating in spectrum auctions must submit an electronic application to the FCC disclosing their ownership structure and identifying the markets/licenses on which they intend to bid.

Approximately 2 weeks after the filing deadline and 2 weeks before the start of the auction, potential bidders must submit a refundable deposit that is used to purchase the bidding units required to place bids in the auction. This deposit is not refundable after the auction closes. At a minimum, an applicant’s total up-front payment must be enough to establish eligibility to bid on at least one of the licenses applied for, or else the applicant will not be eligible to participate in the auction.

In calculating the upfront payment amount, an applicant should determine the maximum number of bidding units it may wish to bid on in any single round and submit a payment that covers that number of bidding units. Bidders have to check their calculations carefully because there is no provision for increasing a bidder’s maximum eligibility after the up-front payment deadline.

About 10 days before the auction, qualified bidders receive their confidential bidding access codes, Automated Auction System software, telephonic bidding phone number, and other documents necessary to participate in the auction. Five days before the start of the auction, the FCC sponsors a mock auction that allows bidders to work with the software, become comfortable with the rules and the conduct of a simultaneous multipleround auction, and familiarize themselves with the telephonic bidding process.

When the auction starts, it continues until all bidding activity has stopped on all licenses. To ensure the competitiveness and integrity of the auction process, the rules prohibit applicants for the same geographic license area from communicating with each other during the auction about bids, bidding strategies, or settlements. The winning bidders for spectrum in each market are awarded licenses.

Within 10 business days, each winning bidder must submit sufficient funds (in addition to its upfront payment) to bring its total amount of money on deposit to 20 percent of its net winning bids (actual bids less any applicable bidding credits). Up-front payments are applied first to satisfy the penalty for any withdrawn bid before being applied toward down payments.

If a company fails to pay on time, the FCC takes back the licenses and holds them for a future auction. The licenses are granted for a 10-year period, after which the FCC can take them back if the holder fails to provide service over that spectrum.

The FCC’s simultaneous multiple-round auction methodology and the AAS software have generated interest worldwide. The FCC has demonstrated the system to representatives of many countries, including Argentina, Brazil, Canada, Hungary, Peru, Russia, South Africa, and Vietnam. Mexico licensed the FCC’s copyrighted system and has used it successfully in a spectrum auction. In addition, in 1997, the FCC was awarded a bronze medal from the Smithsonian Institution for recognition of the visionary use of information technology.

Specialized Mobile Radio

2010-11-12T18:15:00.001-08:00

Specialized Mobile Radio (SMR) is used to provide two-way radio dispatch service for the public safety, construction, and transportation industries. In 1979, the FCC established SMR service in the 800-MHz band and, in 1986, established SMR service in the 900-MHz band. Although SMR is used primarily for voice communications, such systems also support data and facsimile services.

Generally, SMR systems provide dispatch services for companies with multiple vehicles using the “push to talk” method of communication. Atraditional SMR system consists of one or more base station transmitters, one or more antennas, and mobile radio units obtained from the SMR operator for a fee or purchased from a retail source.

SMR has limited roaming capabilities, but its range may be extended through interconnection with the Public Switched Telephone Network (PSTN), as if the user were a cellular subscriber. Both types of services operate over different assigned frequencies within the range of 800 to 900 MHz. Cellular services are assigned to bands between 824 and 849 MHz and 869 and 894 MHz.

SMR networks traditionally used one large transmitter to cover a wide geographic area. This limited the number of subscribers because only one subscriber could talk on one frequency at any given moment. The number of frequencies allocated to SMR is smaller than for cellular, and there have been several operators in each market. Because dispatch messages are short, SMR services were able to work reasonably well.

The 800-MHz SMR systems operate on two 25-kHz channels paired, while the 900-MHz systems operate on two 12.5-kHz channels paired. Because of the different sizes of the channel bandwidths allocated for 800- and 900-MHz systems, the radio equipment used for 800-MHz SMR is not compatible with the equipment used for 900-MHz SMR systems. SMR systems consist of two distinct types: conventional and trunked systems.

A conventional system allows an end user the use of only one channel. If someone else is already using that end user’s assigned channel, that user must wait until the channel is available. In contrast, a trunked system combines channels and contains processing capabilities that automatically search for an open channel. This search capability allows more users to be served at any one time. Amajority of the current SMR systems are trunked systems.

In 1993, Congress reclassified most SMR licensees as Commercial Radio Service (CMRS) providers and established the authority to use competitive bidding to issue new licenses. With the development of digital systems, the SMR marketplace now offers new services such as acknowledgment paging and inventory tracking, credit card authorization, automatic vehicle location, fleet management, inventory tracking, remote database access, and voice mail.

Software-Defined Radios

2010-11-12T18:14:00.001-08:00

Software-defined radios can be reprogrammed quickly to transmit and receive on multiple frequencies in different transmission formats. This reprogramming capability could change the way users traditionally communicate across wireless services and promote more efficient use of radio spectrum.

In a software-defined radio, functions that were formerly carried out solely in hardware, such as generation of the transmitted radio signal and tuning of the received radio signal, are performed by software. Because these functions are carried out in software, the radio is programmable, allowing it to transmit and receive over a wide range of frequencies and to emulate virtually any desired transmission format.

The concept of software-defined radio originated with the military, where it was used quickly for electronic warfare applications. Now the cellular/wireless industries in the United States and Europe have begun work to adapt the technology to commercial communications services in the hope of realizing its long-term economic benefits.

If all goes according to plan, future radio services will provide seamless access across cordless telephone, wireless local loop, Personal Communications Services (PCS), mobile cellular, and satellite modes of communication, including integrated data and paging.

Generations of Radio Systems

First-generation hardware-based radio systems are built to receive a specific modulation scheme. Ahandset would be built to work over a specific type of analog network or a specific type of digital network. The handset worked on one network or the other, but not both, and it could certainly not cross between analog and digital domains. Second-generation radio systems also are based in hardware.

Miniaturization enables two sets of components to be packaged into a single, compact handset. This enables the unit to operate in dual mode—for example, switching between Advanced Mobile Phone Service (AMPS) or TDMA modulation as necessary. Such handsets are implemented using snap-in components: Two existing chip sets—one for AMPS and one for TDMA, for example—are used together.

Building such handsets typically costs only 25 to 50 percent more than a single-mode handset but offers network operators and users far more flexibility. Handsets that work across four or more modes/bands entail far more complexity and processing power and call for a different architecture altogether. The architecture is based in software and programmable digital signal processors (DSPs). This architecture is referred to as “software-defined radio” or just “software radio.”

It represents the third generation of radio systems. As new technologies are placed onto existing networks and wireless standards become more fragmented—particularly in the United States—the need for a single radio unit that can operate in different modes and bands becomes more urgent. Asoftware radio handset could, for example, operate in a GSM-based PCS network, a legacy AMPS network, and a future satellite mobile network.

Operation

As noted, a software radio is one in which channel modulation waveforms are defined in software. Waveforms are generated as sampled digital signals, converted from digital to analog via a wideband digital-to-analog converter (DAC), and then up-converted from an intermediate frequency (IF) to the desired radiofrequency (RF).

In similar fashion, the receiver employs a wideband analog-to-digital converter (ADC) that captures all the channels of the software radio node. The receiver then extracts, down-converts, and demodulates the channel waveform using the software loaded on a general-purpose processor.

Multimode/Multiband

As competing technologies for wireless networks emerged in the early 1990s, it became apparent that subscribers would have to make a choice: The newer digital technologies offered more advanced features, but coverage would be spotty for some years to come. The older analog technologies offered wider coverage but did not support the advanced features. A compromise was offered in the form of wireless multimode/ multiband systems that offered subscribers the best of both worlds.

At the same time, wireless multimode/multiband systems allow operators to economically grow their networks to support new services where the demand is highest. With multimode/ multiband handsets, subscribers can access new digital services as they become available while retaining the capability to communicate over existing analog networks.

The wireless system gives users access to digital channels wherever digital service is available while providing a transparent handoff when users roam between cells alternately served by various digital and analog technologies. As long as subscribers stay within cells served by advanced digital technologies, they will continue to enjoy the advantages provided by these technologies.

When they reach a cell that is supported by analog technology, they will have access only to the features supported by that technology. The intelligent roaming capability of multimode/multiband systems automatically chooses the best system for the subscriber to use at any given time. Third-generation radio systems are frequency-agile and extend this flexibility even further by supporting more modes and bands.

It is important to remember, however, that software radio systems may never catch up to encompass all the modes and bands that are available today and that may become available in the future. Users will always be confronted by choices. Making the right choice will depend on calling patterns, the features associated with the different technologies and standards, and the type of systems in use at international locations visited most frequently.

Multimode and multiband handsets have been available from several manufacturers since 1995. These handsets support more than one technology for their mode of operation and more than one frequency band. An example of a multimode wireless system is one that supports both AMPS and Narrowband AMPS (N-AMPS). Narrowband AMPS is a system-overlay technology that offers enhanced digital-like features, such as Digital Messaging Service, to phones operating in a traditional analog-based AMPS network.

Among the vendors offering dual-mode AMPS/N-AMPS handsets is Nokia, the world’s second-largest manufacturer of cellular phones. An example of a multiband wireless system is one that supports GSM at both 900 and 1800 MHz in Europe. Among the vendors offering dual-band GSM handsets is Motorola. The company’s International 8800 Cellular Telephone allows GSM 1800 subscribers to roam on either their home or GSM 900 networks (where roaming agreements are in place) using a single cellular telephone.

Of course, handsets can be both multimode and multiband. Ericsson, for example, offers dual-band/dual-mode handsets that support communication over both 800-MHz AMPS/Digital AMPS (D-AMPS) and 1900-MHz D-AMPS networks. Subscribers on a D-AMPS 1900 channel can hand off both to and from a D-AMPS channel on 800 MHz as well as to and from an analog AMPS channel.

Multimode and multiband wireless systems allow operators to expand their networks to support new services where they are needed most, expanding to full coverage at a pace that makes economic sense. From the subscribers’ perspective, multimode and multiband wireless systems allow them to take advantage of new digital services that are initially deployed in large cities while still being able to communicate in areas served by the older analog technologies.

With its multimode capabilities, the wireless system preferentially selects a digital channel wherever digital service is available. If the subscriber roams out of the cell served by digital technology—from one served by CDMAto one served by AMPS, for example—a handoff occurs transparently. As long as subscribers stay within CDMAcells, they will continue to enjoy the advantages the technology provides, such as better voice quality and soft handoff, which virtually eliminates dropped calls.

When subscribers reach a cell that supports only AMPS, voice quality diminishes and the chances for dropped calls increases. However, these multimode/multiband handsets are not software-programmable. They rely instead on packaging dual sets of hardware in the same handset.

Miniaturization of the various components makes this both practical and economical, but this approach has its limitations when the number of modes and frequencies that must be supported goes beyond two or three. Beyond that point, a totally new approach is required that relies more on programmable components.

Regulation

Despite the promising concept of software-defined radios, the rollout of consumer products that use the technology has been slow. In September 2001, the FCC adopted rule changes to accommodate the authorization and deployment of software-defined radios. Under the previous rules, if a manufacturer wanted to make changes to the frequency, power, or type of modulation for an approved transmitter, a new approval was required, and the equipment had to be relabeled with a new identification number.

Because software-defined radios have the capability of being reprogrammed in the field, these requirements could be overly burdensome and hinder the deployment of software-defined radios to consumers. Under the new rules, software modifications in a software-defined radio can be made through a “permissive change” that has a streamlined filing process.

The FCC identification number will not have to be changed, so equipment in the field will not have to be relabeled. These permissive changes can be obtained only by the original grantee of the equipment authorization. To allow for changes to equipment by other parties such as software developers, the FCC will permit an optional “electronic label” for software-defined radios, in which the FCC identification number could be displayed on a liquid-crystal display (LCD) or similar screen.

It will allow another party to obtain an equipment approval in its name and become the party responsible for compliance instead of the original grantee. The FCC also requires that a grantee take adequate steps to prevent unauthorized software modifications to radios, but it declined to set specific security requirements at this time. This will allow manufacturers flexibility to develop innovative equipment while at the same time provide for oversight of the adequacy of such steps through the equipment authorization process.

Software radio architectures not only reduce the complexity and expense of serving a diverse customer base, they also simplify the integration and management of rapidly emerging standards. With software-based radio systems, access points, cell sites, and wireless data network hubs can be reprogrammed to meet changing standards requirements instead of replacing them or maintaining them in parallel with a newer infrastructure.

From the perspective of users, the same hardware would continue to be used—only the software gets upgraded. This could signal the end of outdated cellular telephones. Consumers will be able to upgrade their phones with new applications—much as they would purchase new programs to add new capabilities to their computers. Although the benefits are clear, commercial software-defined radio systems are still a few years away. Until they become available, users will have to make do with the current generation of multimode/multiband handsets.

Short Messaging Service

2010-11-12T18:13:00.001-08:00

Short Messaging Service (SMS) is the ability to send and receive text messages between mobile telephones over cellular networks. Once used exclusively by carriers to push notifications of new voice messages down to smart cell phones, SMS is now on a fast track to universal adoption by the cellular subscribers around the world, who have adopted it as a two-way personal messaging medium.

Created as part of the Global System for Mobile (GSM) Phase 1 standard, the first short message was sent in December 1992 from a PC to a mobile phone on the Vodafone GSM network in the United Kingdom. With SMS, subscribers can send up to 160 characters of text when Latin alphabets are used and 70 characters when non-Latin alphabets such as Arabic and Chinese are used. The text can consist of words or numbers or an alphanumeric combination.

The success of SMS can be attributed to certain unique features, such as message storage if the recipient is not available, confirmation of short message delivery, and simultaneous transmission with GSM voice, data, and fax services. The person receiving the message also will know the phone number of the sender and the time at which the message was sent.

While its principal use is still for personal messaging, SMS is also being used for receiving weather reports and traffic information, mobile shopping, banking, and stock trading. SMS is being enhanced to support the delivery of long-text messages, images, and video as well.

Although the prospects for SMS in the United States look promising, its rollout has been hampered by interoperability problems between different carriers. While all European carriers have standardized on GSM, carriers in the United States use several competing technologies. As a result, AT&T’s message service will only work between other AT&T wireless customers or other carriers using its TDMAtransmission technology.

Likewise, Sprint PCS message-service customers would be able to communicate only with other Sprint PCS customers or other carriers using its CDMA transmission technology. Fortunately, gateway systems are being deployed that permit messages to be transmitted between customers on different carrier networks. Most premises-based mobile-access gateways and servers already provide interfaces to SMS.

A growing number of service providers offer SMS backbone-routing services to bridge otherwise-incompatible SMS carrier services. For example, TeleCommunication Systems introduced technology that allows intercarrier text messaging through use of a customer’s phone number. InfoSpace added wireless network SMS interoperability to its technology platform that already enables Internet content and mobile-commerce services via several wireless carriers.

Software developed by InphoMatch enables AT&T Wireless customers to send text messages to other wireless carriers’ customers. The growth prospects for SMS look so good that traditional paging services may one day disappear. Motorola has already announced that it is pulling out of the market for traditional paging infrastructure and handsets in favor of developing two-way technologies for use in wireless phones.

The company’s Wireless Messaging Division will now focus on providing SMS products for use on networks for GSM, General Packet Radio Services (GPRS), and CDMAprotocols. At the same time, Motorola announced that it is discontinuing products that support the ReFlex protocol, which Motorola developed in the 1990s for traditional two-way paging carriers such as Skytel and Arch Wireless.

AT&T Wireless was the first national carrier to bring SMS to the United States and is the current market leader. AT&T claims to handle 35 million text messages a month. Two plans are available for the two-way text-messaging service. The first has no monthly charge, and the user pays $0.10 per message sent. The second has a monthly charge of $4.99 per month with 100 included outgoing messages and $0.10 per message thereafter.

Both plans offer unlimited incoming messages and allow messages to be sent to subscribers of other carriers at no additional charge. The service also offers features that let users reply, forward, store, and retrieve messages right from their phone. Messages of up to 150 characters can be sent between compatible phones and to Internet e-mail addresses—including e-mail addresses for pagers, handheld devices, or Webenabled phones.

Among the mobile phones offered by AT&T Wireless that are compatible with its 2-Way Text Messaging service are the Nokia 5165, 3360, and 8260. Since November 2001, AT&T Wireless customers have had the ability to send text messages to virtually any wireless phone regardless of the carrier simply by knowing the recipient’s phone number.

The intercarrier text messaging capability is available to postpaid and prepaid subscribers in all the company’s TDMAand GSM markets. InphoMatch, a wireless messaging solution provider, supplies the software for the intercarrier messaging services. InphoMatch’s routing system sends messages between and across U.S. carriers simply by using a wireless phone number while remaining transparent to the customer.

Other service providers in the United States now offer SMS. The two-way text messaging service of Cingular is Interactive Messaging, which allows up to 150 characters. Users send text messages via the 10-digit mobile number of the recipient, regardless of which wireless service the recipient happens to have. Sprint PCS offers an SMS-based service called Short Mail, which allows users to send messages of up to 100 characters from one Sprint PCS phone to another.

Verizon Wireless offers its SMS-based service, called Mobile Messenger, which allows users to send short text messages of up to 160 characters between handsets or any Internet e-mail system. Voicestream’s two-way messaging service is called Ping Pong. It allows text messages of up to 140 characters to be sent and received between wireless devices using only an e-mail address.

In the same way instant messaging (IM) on the Internet has become a standard method of communication among U.S. teenagers, SMS will provide a choice that will grow the total messaging market and, in some cases, replace voice traffic and IM. Desktop-to-desktop IM is not conducive to mobility. Even desktop-to-mobile IM inhibits mobility because a cellular subscriber using a limited screen and keyboard cannot keep up with messaging traffic generated from a fully featured desktop. Unlike SMS, IM clients operating on wireless devices have proven complex, cumbersome, and difficult to use.

Mobile Satellite Communications

2010-11-12T18:12:00.003-08:00

Mobile satellite communications are used by the airline, maritime, and shipping industries. Among the key providers of mobile satellite communications services are Inmarsat, Intelsat, and Comsat. All began as government entities but, through global privatization efforts, have become private corporations that compete for market share.

Inmarsat The International Maritime Satellite Organization (Inmarsat) was formed in the late 1970s as a maritime-focused intergovernmental organization. Inmarsat completed its transition to a limited company in 1999 and now serves a broad range of markets.

Today, Inmarsat delivers its solutions— including telex, voice, data, and video transmission—through a global distribution network of approximately 200 distributors and other service providers operating in over 150 countries to end users in the maritime, land, and aeronautical sectors.

At year end 2000, approximately 212,000 terminals were registered to access Inmarsat services. Inmarsat’s primary satellite constellation consists of four Inmarsat-3 satellites in geostationary orbit. Between them, the global beams of the satellites provide overlapping coverage of the whole surface of the earth, apart from the poles. The Inmarsat-3 satellites are backed up by a fifth Inmarsat-3 and four previous-generation Inmarsat-2s, also in geostationary orbit.

A key advantage of the Inmarsat-3s over their predecessors is their ability to generate a number of spot beams as well as single large global beams. Spot beams concentrate extra power in areas of high demand and make it possible to supply standard services to smaller, simpler terminals.

Among Imarsat’s newest services is Swift64, which uses its Global Area Network platform to offer airlines and users of corporate jets the ability to operate an Integrated Services Digital Network (ISDN) connection of up to 64 kbps or a Mobile Packet Data connection using the existing Inmarsat antenna already installed on almost 80 percent of modern long-haul jets, as well as over 1000 corporate jets.

With Swift64, airlines will be able to provide passengers with an ISDN 64-kbps bearer channel that is billed according to connection time. Mobile Packet Data, on the other hand, offers an “always on” connection that is billed according to the number of packets sent. These services enable users to surf the Web and send and receive e-mails and documents across all the continents of the world outside the north and south poles.

Intelsat Another provider on international mobile satellite communications services is Intelsat, which has the widest distribution network of any satellite communications company. Operating since 1964, Intelsat has a global fleet of 21 satellites from which it offers wholesale Internet, broadcast, telephony, and corporate network solutions to leading service providers in more than 200 countries and territories worldwide.

Seven more satellites will be put into operation in the next 2 years to broaden coverage and add capacity. In mid-2001, Intelsat completed its transformation from a treaty-based organization to a privately held company with over 200 shareholders composed of companies from more than 145 countries.

Comsat In the United States, the government-sponsored satellite company was Comsat, which had been the only authorized U.S. organization that could directly access the Intelsat system. Lockheed Martin’s acquisition of Comsat in August 2000 ended the 38-year history of quasi-government backing for Comsat. The federal government created the company in 1962 to prevent AT&T, then a telephone monopoly, from extending its monopoly to the satellite communications sector.

Comsat became a publicly traded company the next year, but Congress ordered that no single investor could own a majority stake in the company because it was the only American firm with access to Intelsat. Congress eliminated the exclusive right to access Intelsat as part of the agreement that allowed Lockheed Martin to purchase Comsat.

Satellites provide a reliable, economical way of providing communications to remote locations and supporting mobile telecommunications. Taking into account the large number of satellites that can be employed, along with their corresponding radiofrequency assignments, it is clear that satellite communications systems offer ample room for expansion.

Conversion of satellite transmissions from analog to digital and use of more sophisticated multiplexing techniques will further increase satellite transmission capacity. Other technological advances are focusing on the higher frequency bands—applying them in ways that decrease signal degradation.

Satellites Communication

2010-11-12T18:12:00.001-08:00

The idea of using satellites as relay stations for an international microwave radiotelephone system goes back to 1945 when Arthur C. Clarke proposed the scheme in a British technical journal. Clarke, then a young scientist and officer of the Royal Air Force, later became a leading science fiction writer and coauthor of the motion picture 2001: ASpace Odyssey. However, it was not until 1957 that the first satellite was put into orbit.

Although just a beacon whose primary purpose was to announce its presence in the sky, the successful orbital deployment of the 185-pound Russian Sputnik sparked a technological revolution in communications that continues to this day. There are now over 2560 satellites in orbit, along with over 6000 pieces of debris tracked by the National Aeronautics and Space Administration (NASA).

The United States launched the first communication satellites in the early 1960s. Echo 1 and Echo 2 were little more than metallic balloons that simply reflected microwave signals from point A to point B. These passive satellites could not amplify the signals. Reception was often poor and the range of transmission limited. Ground stations had to track them across the sky, and communication between two ground stations was only possible for a few hours a day when both had visibility with the satellite at the same time.

Later, geostationary satellites overcame this problem. Such systems were high enough in orbit to move with the earth’s rotation, in effect giving them fixed positions so that they could provide communications coverage to specific areas. Satellites are now categorized by type of orbit and area of coverage as follows:

Geostationary-earth-orbit (GEO) satellites orbit the equator in a fixed position about 23,000 miles above the earth. Three GEO satellites can cover most of the planet, with each unit capable of handling 20,000 voice calls simultaneously. Because of their large coverage “footprint,” these satellites are ideal for radio and television broadcasting and long distance domestic and international communications.

Middle-earth-orbit (MEO) satellites circle the earth at about 6000 miles up. It takes about 12 satellites to provide global coverage. The lower orbit reduces power requirements and transmission delays that can affect signal quality and service interaction.

Low-earth-orbit (LEO) satellites circle the earth only 600 miles up (Figure S-2). As many as 200 satellites may be required to provide global coverage. Since their low altitude means that they have nonstationary orbits and they pass over a stationary caller rather quickly, calls must be handed off from one satellite to the next to keep the session alive. The omnidirectional antennas of these devices do not have to be pointed at a specific satellite. There is also very little propagation delay. And the low altitude of these satellites means that earthbound transceivers can be packaged as low-powered, inexpensive hand-held devices.

The International Telecommunication Union (ITU) is responsible for all frequency/orbit assignments. Through its International Bureau, the Federal Communications Commission (FCC) regulates all satellite service rates, competition among carriers, and international telecommunications traffic in the United States, ensuring that U.S. satellite operators conform to ITU frequency and orbit assignments. The FCC also issues licenses to domestic satellite service providers.

Satellite Technology

Each satellite carries transponders, which are devices that receive radio signals at one frequency and convert them to another for transmission. The uplink and downlink frequencies are separated to minimize interference between transmitted and received signals. Satellite channels allow one sending station to broadcast transmissions to one or more receiving stations simultaneously.

In a typical scenario, the communications channel starts at a host computer, which is connected through a traditional telephone company medium to the central office (i.e., master earth station or hub) of the satellite communications vendor. The data from this and other local loops are multiplexed into a fiberoptic or microwave signal and sent to the satellite vendor’s earth station.

This signal becomes part of a composite transmission that is sent by the earth station to the satellite (uplink) and then transmitted by the satellite to the receiving earth stations (downlink). At the receiving earth station, the data are transferred by a fiberoptic or microwave link to the satellite carrier’s central office. The composite signal is then separated into individual communications channels that are distributed over the Public Switched Telephone Network (PSTN) to their destinations.

Satellite communication is very reliable for data transmission. The bit error rate (BER) for a typical satellite channel is in the range of 1 error in 1 billion bits transmitted. However, a potential problem with satellite communication is delay. Round-trip satellite transmission takes approximately 500 milliseconds, which can hamper voice communications and create significant problems for real-time interactive data transmissions.

For voice communications, digital echo cancelers can correct voice echo problems caused by the transmission delay. Anumber of techniques are employed to nullify the effects of delay during data transmissions via satellite. One technique employed by Mentat, Inc., increases the performance of Internet and intranet access over satellites by transparently replacing the Transmission Control Protocol (TCP) over the satellite link with a protocol optimized for satellite conditions.

The company’s SkyX Gateway intercepts the TCP connection from the client and converts the data to a proprietary protocol for transmission over the satellite. The gateway on the opposite side of the satellite link translates the data back to TCP for communication with the server. The result is vastly improved performance while the process remains transparent to the end user and fully compatible with the Internet infrastructure. No changes are required to the client or server, and all applications continue to function without modification.

Very Small Aperture Terminals (VSATs)

VSAT networks have evolved to become mainstream communication networking solutions that are affordable to both large and small companies. Today’s VSAT is a flexible, softwareintensive system built around standard communications protocols. With a satellite as the serving office and using radiofrequency (RF) electronics instead of copper or fiber cables, these systems can be truly considered packet-switching systems in the sky.

VSATs can be configured for broadcast (one-way) or interactive (two-way) communications. The typical star topology provides a flexible and economical means of communications with multiple remote or mobile sites. Applications include broadcasting database information, insurance agent support, reservations systems, retail point-of-sale credit card checking, and interactive inventory data sharing.

Today’s VSATs are used for supporting high-speed message broadcasting, image delivery, integrated data and voice, and mobile communications. VSATs are used increasingly for supporting local area network (LAN)–to-LAN connectivity and LAN-to–wide area network (WAN) bridging, as well as for providing route and media diversity for disaster recovery.

To make VSAT technology more affordable, VSAT providers offer compact hubs and submeter antennas that provide additional functionality at approximately 33 percent less than the cost of full-size systems. Newer submeter antennas are even supporting direct digital TV broadcasts to the home.

Network Management

The performance of the VSAT network is monitored increasingly at the hub location by the network control system. A failure anywhere on the network automatically alerts the network control operator, who can reconfigure capacity among individual VSAT systems. In the case of signal fade due to adverse weather conditions, for example, the hub detects the weak signal—or the absence of a signal—and alerts the network operations staff so that corrective action can be taken.

Today’s network management systems indicate whether power failures are local or remote. They also increasingly locate the source of communications problems and determine whether the trouble is with the software or hardware. Such capabilities often eliminate the expense of dispatching technicians to remote locations. And when technicians must be dispatched, the diagnostic capabilities of the network management system can ensure that service personnel have the appropriate replacement parts, test gear, software patch, and documentation with them to solve the problem in a single service call.

Overall link performance is determined by the BER, network availability, and response time. Because of the huge amount of information transmitted by the hub station, uplink performance requirements are more stringent. A combination of uplink and downlink availability, coupled with BER and response time, provides the network control operator with overall network performance information on a continuous basis.

The VSAT’s management system provides an interface to the major enterprise management platforms for single-point monitoring and control and offers a full range of accounting, maintenance, and data flow statistics, including those for inbound versus outbound data flow, peak periods, and total traffic volume by node. Also provided are capabilities for identifying fault conditions, performing diagnostics, and initiating service restoration procedures.

Communications Protocols

Within the VSAT network there are three categories of protocols—those associated with the backbone network, those of the host computer, and those concerned with transponder access. The scope and functionality of protocol handling differ markedly among VSAT network providers. The backbone network protocol is responsible for flow control, retransmissions of bad packets, and running concurrent multiple sessions.

The backbone network protocol could be associated with either the host or the communications link. The host protocol is related to the user application interface, which provides a compatible translation between the backbone protocol and the host communications protocol. Several host protocols are used in VSAT networks, including SNA/SDLC, 3270 Base Station Controller (BSC), Poll Select, and HASP. Multiple protocols can be used at the same VSAT location.

Transponder access protocols are used to assign transponder resources to various VSATs on the network. The three key transponder access protocols that are used on VSAT networks include Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA).

Frequency Division Multiple Access With FDMA, the radiofrequency is partitioned so that bandwidth can be allocated to each VSAT on the network. This permits multiple VSATs to simultaneously use their portion of the frequency spectrum.

Time Division Multiple Access With TDMA, each VSAT accesses the hub via the satellite by the bursting of digital information onto its assigned radiofrequency carrier. Each VSAT bursts at its assigned time relative to the other VSATs on the network. Dividing access in this way—by time slots— is inherently wasteful because bandwidth is available to the VSAT in fixed increments whether or not it is needed. To improve the efficiency of TDMA, other techniques are applied to ensure that all the available bandwidth is used, regardless of whether the application contains bursty or streaming data. Areservation technique can even be applied to ensure that bandwidth is available for priority applications.

Code Division Multiple Access With CDMA, all VSATs share the assigned frequency spectrum and also can transmit simultaneously. This is possible through the use of spreadspectrum technology, which employs a wideband channel as opposed to the narrowband channels employed by other multiple access techniques such as FDMAand TDMA. Over the wideband channel, each transmission is assigned a unique code—a long row of numbers resembling a combination to a lock. The outbound data streams are coded so that they can be identified and received only by the station(s) having that code. This technique is also used in mobile communications as a means of cutting down interference and increasing available channel capacity by as much as 20 times.

Rural Radiotelephone Service

2010-11-12T18:11:00.003-08:00

Rural Radiotelephone Service is a fixed wireless service that allows common carriers to provide telephone service to the homes of subscribers living in extremely remote rural areas, where it is not feasible to provide telephone service by wire or other means. Rural Radiotelephone Stations, operating in the paired 152- to 158-MHz and 454- to 459-MHz bands, employ standard duplex analog technology to provide telephone service to subscribers’ homes.

The quality of conventional rural radiotelephone service is similar to that of precellular mobile telephone service. Several subscribers may have to share a radio-channel pair (similar to party-line service), each waiting until the channel pair is not in use by the others before making or receiving a call. Rural Radiotelephone Service is generally considered by state regulators to be a separate service that is interconnected to the Public Switched Telephone Network (PSTN). This service has been available to rural subscribers for more than 25 years.

Carriers must apply to the FCC for permission to offer Rural Radiotelephone Service. Among other things, each application for a central office station must contain an exhibit showing that it is impractical to provide the required communication service by means of landline facilities.

Router

2010-11-12T18:11:00.001-08:00

A router operates at Layer 3 of the Open Systems Interconnection (OSI) reference model, the Network Layer. The device distinguishes among network layer protocols— such as IP, IPX, and AppleTalk—and makes intelligent packet delivery decisions using an appropriate routing protocol. Used on wired and wireless networks, routers can be used to segment a network with the goals of limiting broadcast traffic and providing security, control, and redundant paths.

A router also can provide multiple types of interfaces, including those for T1, Frame Relay, Integrated Services Digital Network (ISDN), Asynchronous Transfer Mode (ATM), cable networks, and Digital Subscriber Line (DSL) services, among others. Some routers can perform simple packet filtering to control the kind of traffic that is allowed to pass through them, providing a rudimentary firewall service. Larger routers can perform advanced firewall functions.

Arouter is similar to a bridge in that both provide filtering and bridging functions across the network. But while bridges operate at the Physical and Data Link Layers of the OSI reference model, routers join LANs at the Network Layer. Routers convert LAN protocols into WAN protocols and perform the process in reverse at the remote location. They may be deployed in mesh as well as point-to-point networks and, in certain situations, can be used in combination with bridges.

Although routers include the functionality of bridges, they differ from bridges in the following ways: They generally offer more embedded intelligence and, consequently, more sophisticated network management and traffic control capabilities than bridges. Another distinction—perhaps the most significant one—between a router and a bridge is that a bridge delivers packets of data on a “best effort” basis, specifically, by discarding packets it does not recognize onto an adjacent network.

Through a continual process of discarding unfamiliar packets, data get to theirs proper destination—on a network where the bridge recognizes the packets as belonging to a device attached to its network. By contrast, a router takes a more intelligent approach to getting packets to their destination— by selecting the most economical path (i.e., least number of hops) on the basis of its knowledge of the overall network topology, as defined by its internal routing table. Routers also have flow-control and error-protection capabilities.

Types of Routing

There are two types of routing: static and dynamic. In static routing, the network manager configures the routing table to set fixed paths between two routers. Unless reconfigured, the paths on the network never change. Although a static router will recognize that a link has gone down and issue an alarm, it will not automatically reroute traffic.

A dynamic router, on the other hand, reconfigures the routing table automatically and recalculates the most efficient path in terms of load, line delay, or bandwidth. In wired networks, some routers balance the traffic load across multiple access links, providing an N × T1 inverse multiplexer function. This allows multiple T1 access lines operating at 1.544 Mbps each to be used as a single higher-bandwidth facility.

If one of the links fails, the other links remain in place to handle the offered traffic. As soon as the failed link is restored to service, traffic is spread across the entire group of lines as in the original configuration.

Routing Protocols

Each router on the network keeps a routing table and moves data along the network from one router to the next using such protocols as the Open Shortest Path First (OSPF) protocol and the Routing Information Protocol (RIP). Although still supported by many vendors, RIP does not perform well in today’s increasingly complex networks. As the network expands, routing updates grow larger under RIP and consume more bandwidth to route the information.

When a link fails, the RIP update procedure slows route discovery, increases network traffic and bandwidth usage, and may cause temporary looping of data traffic. Also, RIP cannot base route selection on such factors as delay and bandwidth, and its line-selection facility is capable of choosing only one path to each destination. The newer routing standard, OSPF, overcomes the limitations of RIP and even provides capabilities not found in RIP.

The update procedure of OSPF requires that each router on the network transmit a packet with a description of its local links to all other routers. On receiving each packet, the other routers acknowledge it, and in the process, distributed routing tables are built from the collected descriptions. Since these description packets are relatively small, they produce a minimum of overhead. When a link fails, updated information floods the network, allowing all the routers to simultaneously calculate new tables.

Types of Routers

Multiprotocol nodal, or hub, routers are used for building highly meshed internetworks. In addition to allowing several protocols to share the same logical network, these devices pick the shortest path to the end node, balance the load across multiple physical links, reroute traffic around points of failure or congestion, and implement flow control in conjunction with the end nodes.

They also provide the means to tie remote branch offices into the corporate backbone, which might use such WAN services as Transmission Control Protocol/Internet Protocol (TCP/IP), T1, ISDN, and ATM. Access routers are typically used at branch offices. These are usually fixed-configuration devices available in Ethernet and Token Ring versions that support a limited number of protocols and physical interfaces.

They provide connectivity to high-end multiprotocol routers, allowing large and small nodes to be managed as a single logical enterprise network. Although low-cost, plug-and-play bridges can meet the need for branch office connectivity, low-end routers can offer more intelligence and configuration flexibility at comparable cost. The newest access routers are multiservice devices that are designed to handle a mix of data, voice, and video traffic.

They support a variety of WAN connections through built-in interfaces that include dual ISDN Basic Rate Interface (BRI) interfaces, dual analog ports, T1/Frame Relay ports, and an ISDN interface for videoconferencing. Such routers can run software that provides Internet Protocol Secure (IPSec) virtual private network (VPN), firewall, and encryption services.

Midrange routers provide network connectivity between corporate locations in support of workgroups or the corporate intranet, for example. These routers can be stand-alone devices or packaged as modules that occupy slots in an intelligent wiring hub or LAN switch. In fact, this type of router is often used to provide connectivity between multiple wiring hubs or LAN switches over high-speed LAN backbones such as ATM, Fiber Distributed Data Interface (FDDI), and Fast Ethernet.

There is a consumer class of routers for 2.4-GHz Wireless Fidelity (Wi-Fi) networks that are capable of providing shared access to the Internet over such broadband technologies as cable and DSL. The EtherFast Wireless AP + Cable/DSL Router from Linksys, for example, connects a wireless network to a high-speed broadband Internet connection and a 10/100 Fast Ethernet backbone.

Configurable through any networked PC’s Web browser, the router can be set up for Network Address Translation (NAT), allowing it to act as an externally recognized Internet device with its own IP address for the home LAN. The Linksys device is also equipped with a four-port Ethernet switch. The combination of wireless router and switch technology eliminates the need to buy an additional hub or switch and extends the range of the wireless network.

Whether used on a wired or wireless network or a hybrid network, routers fulfill a vital role in implementing complex mesh networks such as the Internet and private intranets using Layer 3 protocols, usually IP. They also have become an economical means of tying branch offices into the enterprise network and providing PCs tied together on a home network with shared access to broadband Internet services such as cable and DSL.

Like other interconnection devices, enterprise-class routers are manageable via SNMP, as well as the proprietary management systems of vendors. Just as bridging and routing functions made their way into a single device, routing and switching functions are being combined in the same way.

Repeater

2010-11-12T17:52:00.001-08:00

A repeater is a device that extends the inherent distance limitations of various transmission media, including wireless links, by boosting signal power so that it stays at the same level regardless of the distance it must travel. As such, the repeater operates at the lowest level of the Open Systems Interconnection (OSI) reference model—the Physical Layer.

Repeaters are necessary because signal strength weakens with distance: The longer the path a signal must travel, the weaker it gets. This condition is known as “signal attenuation.” On a telephone call, a weak signal will cause low volume, interfering with the parties’ ability to hear each other. In cellular networks, when a mobile user moves beyond the range of a cell site, the signal fades to the point of disconnecting the call.

In the LAN environment, a weak signal can result in corrupt data, which can substantially reduce throughput by forcing retransmissions when errors are detected. When the signal level drops low enough, the chances of interference from external noise increase, rendering the signal unusable. Repeaters also can be used to link different types of network media—fiber to coaxial cable, for example.

Often LANs are interconnected in a campus environment by means of repeaters that form the LANs into connected network segments. The segments may employ different transmission media—thick or thin coaxial cable, twisted-pair wiring, or optical fiber. The cost of media converters is significantly less than full repeaters and can be used whenever media distance limitations will not be exceeded in the network.

Hubs or switches usually are equipped with appropriate modules that perform the repeater and media conversion functions on sprawling LANs. But the use of hubs or switches also can eliminate the need for repeaters, since most cable segments in office buildings will not run more than 100 feet (about 30 meters), which is well within the distance limitation of most LAN standards, including 1000BaseT Gigabit Ethernet running over Category 5 cable.

Often the terms repeater and regenerator are used interchangeably, but there is a subtle difference between the two. In an analog system, a repeater boosts the desired signal strength but also boosts the noise level as well. Consequently, the signal-to-noise ratio on the output side of the repeater remains the same as on the input side. This means that once noise is introduced into the desired signal, it is impossible to get the signal back into its original form again on the output side of the repeater.

In a digital system, regenerators are used instead of repeaters. The regenerator determines whether the information- carrying bits are 1s or 0s on the basis of the received signal on the input side. Once the decision of 1 or 0 is made, a fresh signal representing that bit is transmitted on the output side of the regenerator.

Because the quality of the output signal is a perfect replication of the input signal, it is possible to maintain a very high level of performance over a range of transmission impairments. Noise, for instance, is filtered out because it is not represented as a 1 or 0.

Stand-alone repeaters have transceiver interface modules that provide connections to various media. There are fiberoptic transceivers, coaxial transceivers, and twistedpair transceivers. Some repeaters contain the intelligence to detect packet collisions and will not repeat collision fragments to other cable segments. Some repeaters also can “deinsert” themselves from a hub or switch when there are excessive errors on the cable segment, and they can submit performance information to a central management station.

RMON II

2010-11-12T17:51:00.003-08:00

The RMON MIB is basically a MAC-level standard. Its visibility does not extend beyond the router port, meaning that it cannot see beyond individual LAN segments. As such, it does not provide visibility into conversations across the network or connectivity between the various network segments. Given the trends toward remote access and distributed workgroups, which generate a lot of intersegment traffic, visibility across the enterprise is an important capability to have.

RMON II extends the packet capture and decoding capabilities of the original RMON MIB to Layers 3 through 7 of the Open Systems Interconnection (OSI) reference model. This allows traffic to be monitored via network-layer addresses—which lets RMON “see” beyond the router to the internetwork—and distinguish between applications.

Analysis tools that support the network layer can sort traffic by protocol rather than just report on aggregate traffic. This means that network managers will be able to determine, for example, the percent of Internet Protocol (IP) versus Internet Packet Exchange (IPX) traffic traversing the network. In addition, these higher-level monitoring tools can map end-to-end traffic, giving network managers the ability to trace communications between two hosts—or nodes—even if the two are located on different LAN segments.

RMON II functions that will allow this level of visibility include:

Protocol directory table Provides a list of all the different protocols a RMON II probe can interpret.
Protocol distribution table Permits tracking of the number of bytes and packets on any given segment that have been sent from each of the protocols supported. This information is useful for displaying traffic types by percentage in graphical form.
Address mapping Permits identification of traffic-generating nodes, or hosts, by Ethernet or Token Ring address in addition to MAC address. It also discovers switch or hub ports to which the hosts are attached. This is helpful in node discovery and network topology applications for pinpointing the specific paths of network traffic.
Network-layer host table Permits tracking of bytes, packets, and errors by host according to individual networklayer protocol.
Network-layer matrix table Permits tracking, by networklayer address, of the number of packets sent between pairs of hosts.
Application-layer host table Permits tracking of bytes, packets, and errors by host and according to application.
Application-layer matrix table Permits tracking of conversations between pairs of hosts by application.
History group Permits filtering and storing of statistics according to user-defined parameters and time intervals.
Configuration group Defines standard configuration parameters for probes that includes such parameters as network address, serial line information, and SNMP trap destination information.

RMON II is focused more on helping network managers understand traffic flow for the purpose of capacity planning rather than for the purpose of physical troubleshooting. The capability to identify traffic levels and statistics by application has the potential to greatly reduce the time it takes to troubleshoot certain problems.

Without tools that can pinpoint which software application is responsible for gobbling up a disproportionate share of the available bandwidth, network managers can only guess. Often it is easier just to upgrade a server or a buy more bandwidth, which inflates operating costs and shrinks budgets.

Token Ring Extensions

2010-11-12T17:51:00.001-08:00

As noted, the first version of RMON defined media-specific objects for Ethernet only. Later, media-specific objects for Token Ring were added.

Token Ring MAC-Layer Statistics This extension provides statistics, diagnostics, and event notification associated with MAC traffic on the local ring. Statistics include the number of beacons, purges, and IEEE 803.5 MAC management packets and events; MAC packets; MAC octets; and ring soft error totals.

Token Ring Promiscuous Statistics This extension collects utilization statistics of all user data traffic (non-MAC) on the local ring. Statistics include the number of data packets and octets, broadcast and multicast packets, and data frame size distribution.

Token Ring MAC-Layer History This extension offers historical views of MAC-layer statistics based on user-defined sample intervals, which can be set from 1 second to 1 hour to allow short- or long-term historical analysis.

Token Ring Promiscuous History This extension offers historical views of promiscuous (i.e., unfiltered) statistics based on user-defined sample intervals, which can be set from 1 second to 1 hour to allow short-term or long-term historical analysis.

Ring Station Control Table This extension lists status information for each ring being monitored. Statistics include ring state, active monitor, hard error beacon fault domain, and number of active stations.

Ring Station Table This extension provides diagnostics and status information for each station on the ring. The type of information collected includes station MAC address, status, and isolating and nonisolating soft error diagnostics.

Source Routing Statistics The extension for source routing statistics is used for monitoring the efficiency of source-routing processes by keeping track of the number of data packets routed into, out of, and through each ring segment. Traffic distribution by hop count provides an indication of how much bandwidth is being consumed by traffic-routing functions.

Ring Station Configuration Control The extension for station configuration control provides a description of the network’s physical configuration. Amedia fault is reported as a “fault domain,” an area that isolates the problem to two adjacent nodes and the wiring between them. The network administrator can discover the exact location of the problem—the fault domain—by referring to the network map.

Some faults result from changes to the physical ring—including each time a station inserts or removes itself from the network. This type of fault is discovered through a comparison of the start of symptoms and the timing of the physical changes. The RMON MIB not only keeps track of the status of each station but also reports the condition of each ring being monitored by a RMON agent.

On large Token Ring networks with several rings, the health of each ring segment and the number of active and inactive stations on each ring can be monitored simultaneously. Network administrators can be alerted to the location of the fault domain should any ring go into a beaconing (fault) condition. Network managers also can be alerted to any changes in backbone ring configuration that could indicate loss of connectivity to an interconnect device such as a bridge or to a shared resource such as a server.

Ring Station Configuration The ring station group collects Token Ring–specific errors. Statistics are kept on all significant MAC-level events to assist in fault isolation, including ring purges, beacons, claim tokens, and such error conditions as burst errors, lost frames, congestion errors, frame copied errors, and soft errors.

Ring Station Order Each station can be placed on the network map in a specified order relative to the other stations on the ring. This extension provides a list of stations attached to the ring in logical ring order. It lists only stations that comply with IEEE 802.5 active monitoring ring poll or IBM trace tool present advertisement conventions.

Remote Monitoring

2010-11-12T17:42:00.003-08:00

The common platform from which to monitor multivendor wireless and wired networks is the Simple Network Management Protocol’s (SNMP’s) Remote Monitoring (RMON) Management Information Base (MIB). Although a variety of SNMPMIBs collect performance statistics to provide a snapshot of events, RMON enhances this monitoring capability by keeping a past record of events that can be used for fault diagnosis, performance tuning, and network planning.

RMON works on wired, wireless and hybrid networks. Hardware- and/or software-based RMON-compliant devices (i.e., probes) placed on each network segment monitor all data packets sent and received. The probes view every packet and produce summary information on various types of packets, such as undersized packets, and events, such as packet collisions. The probes also can capture packets according to predefined criteria set by the network manager or test technician.

At any time, the RMON probe can be queried for this information by a network management application or an SNMP-based management console so that detailed analysis can be performed in an effort to pinpoint where and why an error occurred. The original Remote Network Monitoring MIB defined a framework for the remote monitoring of Ethernet. Subsequent RMON MIBs have extended this framework to Token Ring and other types of networks.

RMON Applications

A management application that views the internetwork, for example, gathers data from RMON agents running on each segment in the network. The data are integrated and correlated to provide various internetwork views that provide end-to-end visibility of network traffic, both local area network (LAN) and wide area network (WAN).

The operator can switch between a variety of views. For example, the operator can switch between a Media Access Control (MAC) view (which shows traffic going through routers and gateways) and a network view (which shows endto- end traffic) or can apply filters to see only traffic of a given protocol or suite of protocols. These traffic matrices provide the information necessary to configure or partition the internetwork to optimize LAN and WAN utilization.

In selecting the MAC level view, for example, the network map shows each node of a segment separately, indicating intrasegment node-to-node data traffic. It also shows total intersegment data traffic from routers and gateways. This combination allows the operator to see consolidated internetwork traffic and how each end node contributes to it. In selecting the network level view, the network map shows end-to-end data traffic between nodes across segments.

By connecting source and ultimate destination without clouding the view with routers and gateways, the operator can immediately identify specific areas contributing to an unbalanced traffic load. Another type of application allows the network manager to consolidate and present multiple segment information, configure RMON alarms, and provide complete Token Ring RMON information, as well as perform baseline measurements and long-term reporting.

Alarms can be set on any RMON variable. Notification via traps can be sent to multiple management stations. Baseline statistics allow longterm trend analysis of network traffic patterns that can be used to plan for network growth.

Ethernet Object Groups

The RMON specification consists of nine Ethernet/Token Ring groups and ten specific Token Ring RMON extensions.

Ethernet Statistics Group The Statistics Group provides segment- level statistics. These statistics show packets, octets (or bytes), broadcasts, multicasts, and collisions on the local segment, as well as the number of occurrences of packets dropped by the agent. Each statistic is maintained in its own 32-bit cumulative counter. Real-time packet size distribution is also provided.

Ethernet History Group With the exception of packet size distribution, which is provided only on a real-time basis, the History Group provides historical views of the statistics provided in the Statistics Group. The History Group can respond to user-defined sampling intervals and bucket counters, allowing for some customization in trend analysis.

The RMON MIB comes with two defaults for trend analysis. The first provides for 50 buckets (or samples) of 30-second sampling intervals over a period of 25 minutes. The second provides for 50 buckets of 30-minute sampling intervals over a period of 25 hours. Users can modify either of these or add additional intervals to meet specific requirements for historical analysis. The sampling interval can range from 1 second to 1 hour.

Host Table Group The RMON MIB specifies a host table that includes node traffic statistics: packets sent and received, octets sent and received, as well as broadcasts, multicasts, and errored packets sent. In the host table, the classification “errors sent” is the combination of packet undersizes, fragments, cyclic redundancy check (CRC)/alignment errors, collisions, and oversizes sent by each node.

The RMON MIB also includes a host timetable that shows the relative order in which the agent discovered each host. This feature is not only useful for network management purposes but also assists in uploading those nodes to the management station of which it is not yet aware. This reduces unnecessary SNMP traffic on the network.

Host Top N Group The Host Top N Group extends the host table by providing sorted host statistics, such as the top 10 nodes sending packets or an ordered list of all nodes according to the errors sent over the last 24 hours. The data selected and the duration of the study are both defined at the network management station. The number of studies that can be run depends on the resources of the monitoring device.

When a set of statistics is selected for study, only the selected statistics are maintained in the Host Top N counters; other statistics over the same time intervals are not available for later study. This processing—performed remotely in the RMON MIB agent—reduces SNMP traffic on the network and the processing load on the management station, which would otherwise need to use SNMP to retrieve the entire host table for local processing.

Alarms Group The Alarms Group provides a general mechanism for setting thresholds and sampling intervals to generate events on any counter or integer maintained by the agent, such as segment statistics, node traffic statistics defined in the host table, or any user-defined packet match counter defined in the Filters Group. Both rising and falling thresholds can be set, each of which can indicate network faults. Thresholds can be established for both the absolute value of a statistic and its delta value, enabling the manager to be notified of rapid spikes or drops in a monitored value.

Filters Group The Filters Group provides a generic filtering engine that implements all packet capture functions and events. The packet capture buffer is filled with only those packets that match the user-specified filtering criteria. Filtering conditions can be combined using the Boolean parameters “and” or “not.” Multiple filters are combined with the Boolean “or” parameter.

Packet Capture Group The types of packets collected depend on the Filter Group. The Packet Capture Group allows the user to create multiple capture buffers and to control whether the trace buffers will wrap (overwrite) when full or stop capturing. The user may expand or contract the size of the buffer to fit immediate needs for packet capturing rather than permanently commit memory that will not always be needed.

Notifications (Events) Group In a distributed management environment, the RMON MIB agent can deliver traps to multiple management stations that share a single community name destination specified for the trap. In addition to the three traps already mentioned—rising threshold and falling threshold (see Alarms Group) and packet match (see Packet Capture Group)—seven additional traps can be specified:

coldStart This trap indicates that the sending protocol entity is reinitializing itself such that the agent’s configuration or the protocol entity implementation may be altered.
warmStart This trap indicates that the sending protocol entity is reinitializing itself such that neither the agent configuration nor the protocol entity implementation is altered.
linkDown This trap indicates that the sending protocol entity recognizes a failure in one of the communication links represented in the agent’s configuration.
linkUp This trap indicates that the sending protocol entity recognizes that one of the communication links represented in the agent’s configuration has come up.
authenticationFailure This trap indicates that the sending protocol entity is the addressee of a protocol message that is not properly authenticated. While implementations of the SNMP must be capable of generating this trap, they also must be capable of suppressing the emission of such traps via an implementation-specific mechanism.
egpNeighborLoss This trap indicates that an External Gateway Protocol (EGP) neighbor for whom the sending protocol entity was an EGP peer has been marked down and the peer relationship is no longer valid.
enterpriseSpecific This trap indicates that the sending protocol entity recognizes that some enterprise-specific event has occurred.

The Notifications (Events) Group allows users to specify the number of events that can be sent to the monitor log. From the log, any specified event can be sent to the management station. The log includes the time of day for each event and a description of the event written by the vendor of the monitor. The log overwrites when full, so events may be lost if not uploaded to the management station periodically.

Traffic Matrix Group The RMON MIB includes a traffic matrix at the MAC layer. A traffic matrix shows the amount of traffic and number of errors between pairs of nodes—one source and one destination address per pair. For each pair, the RMON MIB maintains counters for the number of packets, number of octets, and error packets between the nodes. Users can sort this information by source or destination address.

Applying remote monitoring and statistics-gathering capabilities to the Ethernet environment offers a number of benefits. The availability of critical networks is maximized, since remote capabilities allow for a more timely resolution of the problem. With the capability to resolve problems remotely, operations staff can avoid costly travel to troubleshoot problems on site. With the capability to analyze data collected at specific intervals over a long period of time, intermittent problems can be tracked down that would normally go undetected and unresolved.

Radio Communication Interception

2010-11-12T17:42:00.001-08:00

As the term implies, radio communication interception is the capture of radio signals by a scanning device for the purpose of eavesdropping on a voice call or learning the contents of data messages. When it comes to the interception of radio communications, the Federal Communications Commission (FCC) has the authority to interpret Section 705 of the Communications Act, 47 U.S.C. Section 605, which deals with “Unauthorized Publication of Communications.”

Although the act of intercepting radio communications may violate other federal or state statutes, this provision generally does not prohibit the mere interception of radio communications. For example, if someone happens to overhear a conversation on a neighbor’s cordless telephone, this is not a violation of the Communications Act. Similarly, if someone listens to radio transmissions on a scanner, such as emergency service reports, this is not a violation of Section 705.

A violation of Section 705 would occur, however, if a person were to divulge or publish what he or she hears or use it for his or her own or someone else’s benefit. An example of using an intercepted call for a beneficial use in violation of Section 705 would be someone listening to accident reports on a police channel and then driving or sending one of his or her own tow trucks to the reported accident scene in order to obtain business.

The Communications Act does allow for the divulgence of certain types of radio transmissions. The statute specifies that there are no restrictions on the divulgence or use of radio communications that have been transmitted for the use of the general public, such as transmissions of a local radio or television broadcast station. Likewise, there are no restrictions on divulging or using radio transmissions originating from ships, aircraft, vehicles, or persons in distress.

Transmissions by amateur radio or citizens’ band radio operators are also exempt from interception restrictions. In addition, courts have held that the act of viewing a transmission (such as a pay television signal) that the viewer was not authorized to receive is a “publication” violating Section 705. This section also has special provisions governing the interception of satellite television programming transmitted to cable operators.

The section prohibits the interception of satellite cable programming for private home viewing whether the programming is scrambled or not scrambled but is sold through a marketing system. In these circumstances, authorization must be obtained from the programming provider to legally intercept the transmission. The act also contains provisions that affect the manufacture of equipment used for listening or receiving radio transmissions, such as scanners.

Section 302(d) of the Communications Act, 47 U.S.C. Section 302(d), prohibits the FCC from authorizing scanning equipment that is capable of receiving transmissions in the frequencies allocated to domestic cellular services, that is capable of readily being altered by the user to intercept cellular communications, or that may be equipped with decoders that convert digital transmissions to analog voice audio.

And since April 26, 1994 (47 CFR 15.121), such receivers may not be manufactured in the United States or imported for use in the United States. FCC regulations also prohibit the sale or lease of such scanning equipment (47 CFR 2.803).

Government Interception

While intercepting radio communications for beneficial purposes is illegal in the United States, the federal government systematically engages in such monitoring for the purpose of learning industrial secrets. Under a program known as “Echelon,” a satellite interception system, private and commercial communications are monitored around the world.

The program is run by five nations—the United States, the United Kingdom, Canada, Australia, and New Zealand. France and Russia are also known to have systems of their own. Business is often subject to surveillance involving economic data, such as details of developments in individual sectors of the economy, developments in commodity markets, or compliance with economic embargoes.

Although this is ostensibly the purpose behind Echelon, some countries claim that it is also used for industrial espionage; specifically for spying on foreign businesses with the aim of securing a competitive advantage for firms in the home country. While it is often maintained that Echelon has been used in this way, no such case has been substantiated.

The FCC receives many inquiries regarding the interception and recording of telephone conversations. To the extent that these conversations are radio transmissions, there would be no violation of Section 705 if no divulgence or beneficial use of the conversation takes place. Again, however, the mere interception of some telephone-related radio transmissions—whether cellular, cordless, or landline conversations—may constitute a criminal violation of other federal or state statutes.

Private Land Mobile Radio Services

2010-11-12T17:41:00.001-08:00

Since the 1920s, Private Land Mobile Radio Services (PLMRS) have been meeting the internal communication needs of private companies, state and local governments, and other organizations. These services provide voice and data communications that allow users to control their business operations and production processes, protect worker and public safety, and respond quickly in times of natural disaster or other emergencies.

In 1934, shortly after its establishment, the Federal Communications Commission (FCC) identified four private land mobile services—Emergency Service, Geophysical Service; Mobile Press Service, and Temporary Service, which applied to frequencies used by the motion picture industry. Over the years, the FCC refined these categories.

Until 1997, PLMRS consisted of 20 services spread among six service categories: Public Safety, Special Emergency, Industrial, Land Transportation, Radiolocation, and Transportation Infrastructure. In that year, the FCC did away with 20 discrete radio services and the six service categories and replaced them with two frequency pools: the Public Safety Pool and the Industrial/Business Pool.

Public Safety Radio Pool

The Public Safety Radio Pool was created in 1997. It covers the licensing of the radio communications of state and local governmental entities and the following categories of activities: medical services, rescue organizations, veterinarians, persons with disabilities, disaster-relief organizations, school buses, beach patrols, establishments in isolated places, communications standby facilities, and emergency repair of public communications facilities.

The FCC has established an 800-MHz National Plan that specifies special policies and procedures governing the Public Safety Pool. The principal spectrum resource for the National Plan is the 821- to 824-MHz and the 866- to 869- MHz bands. The National Plan establishes planning regions covering all parts of the United States, Puerto Rico, and the U.S. Virgin Islands. The license application to provide service must be approved by the appropriate regional planning committee before frequency assignments will be made in these bands.

Industrial/Business Pool

The Industrial/Business Pool consists of a number of frequencies that were previously allotted to the Industrial or Land Transportation Radio Services, including the Business Radio Service. Anyone eligible in one of these radio services is eligible in the new Industrial/Business Pool for any frequency in that pool.

In this regard, the FCC has adopted the eligibility criteria from the old Business Radio Service. The Industrial/Business Radio Pool covers the licensing of the radio communications of entities engaged in commercial activities; engaged in clergy activities; operating educational, philanthropic, or ecclesiastical institutions; or operating hospitals, clinics, or medical associations.

General Access Pool

Prior to 1977, channels in the 470- to 512-MHz band were allocated to seven frequency pools based on category of eligibility. The FCC eliminated the separate allocation to these pools and created a General Access Pool to permit greater flexibility and foster more effective and efficient use of the 470- to 512-MHz band. Frequencies in the 470- to 512-MHz band are shared with UHF TV Channels 14 to 20 and are available in only 11 cities.

All unassigned channels, including those which subsequently become unassigned, are considered to be in the General Access Pool and available to all eligible parties on a first-come, first-served basis. If a channel is assigned in an area, however, subsequent authorizations on that channel will only be granted to users from the same category.

Applications for PLMRS

PLMRS are used by organizations that are engaged in a wide variety of activities. Police, fire, ambulance, and emergency relief organizations such as the Red Cross use private wireless systems to dispatch help when emergency calls come in or disaster strikes.

Utility companies, railroad and other transportation providers, and other infrastructurerelated companies use their systems to provide vital day-today control of their systems (including monitoring and control and routine maintenance and repair), as well as to respond to emergencies and disasters—often working with public safety agencies.

A wide variety of businesses, including package delivery companies, plumbers, airlines, taxis, manufacturers, and even the American Automobile Association (AAA), rely on private wireless systems to monitor, control, and coordinate their production processes, personnel, and vehicles.

Although commercial services can serve some of the needs of these organizations, private users generally believe that their own systems provide them with capabilities, features, and efficiencies that commercial services cannot. Some of the requirements and features that PLMRS users believe make their systems unique include:

Immediate access to a radio channel (no dialing required)
Coverage in areas where commercial systems cannot provide service.
Peak usage patterns that could overwhelm commercial systems.
High reliability.
Priority access, especially in emergencies.
Specialized equipment required by the job.

Radio Trunking

In a conventional radio system, a radio can access only one channel at a time. If that channel is in use, the user must either wait for the channel to become idle or manually search for a free channel. Atrunked radio system differs from a conventional system by having the ability to automatically search all available channels for one that is clear. The FCC has recognized two types of trunking: centralized and decentralized.

A centralized trunked system uses one or more control channels to transmit channel-assignment information to the mobile radios. In a decentralized trunked system, the mobile radios scan the available channels and find one that is clear. The rules require that licensees take reasonable precautions to avoid causing harmful interference, including monitoring the transmitting frequency for communications in progress.

This requirement is met in decentralized trunked systems because each mobile unit monitors each channel and finds a clear one on which to transmit. In a centralized trunked radio system, radios typically monitor the control channel(s), not the specific transmit frequencies. Therefore, this form of trunking generally has not been allowed in the shared bands below 800 MHz.

Under certain conditions, however, the FCC allows some licensees to implement centralized trunked radio systems in the shared bands below 800 MHz. Centralized trunking may be authorized if the licensee has an exclusive service area and uses the 470- to 512-MHz band only. If the licensee does not have an exclusive service area, it must obtain consent from all licensees who have cochannel and/or adjacent channel stations.

Private radio systems serve a great variety of communication needs that common carriers and other commercial service providers traditionally have not been able or willing to fulfill. Companies large and small use their private systems to support their business operations, safety, and emergency needs.

The one characteristic that all these uses share—and that differentiates private wireless use from commercial use—is that private wireless licensees use radio as a tool to accomplish their missions in the most effective and efficient ways possible. Private radio users employ wireless communications as they would any other tool or machine—radio contributes to their production of some other good or service.

For commercial wireless service providers, by contrast, the services offered over the radio system are the end products. Cellular, PCS, and Specialized Mobile Radio (SMR) providers sell service or capacity on wireless systems, permitting a wide range of mobile and portable communications that extend the national communications infrastructure. This difference in purpose is significant because it determines how the services are regulated.

Personal Handyphone System

2010-11-12T17:40:00.001-08:00

The Personal Handyphone System (PHS) is a wireless technology that offers high-quality, low-cost mobile telephone services using a fully digital system operating in the 1.9- GHz range. Originally developed by NTT, the Japanese telecommunications giant, PHS is based on the Global System for Mobile (GSM) Telecommunications standard. PHS made its debut in Japan in July 1995, where service was initially offered in metropolitan Tokyo and Sapporo. Although PHS was originally developed in Japan, it is now considered a pan-Asian standard.

Advantages over Cellular

PHS phones (Handyphones) operate at 1.9 GHz, whereas cellular phones operate at 800 MHz. To achieve high voice quality, PHS uses a portion of its capacity to support a highperformance voice-encoding algorithm called Adaptive Differential Pulse Code Modulation (ADPCM). With this algorithm, PHS can support a much higher data throughput (32 kbps) than a cellular-based system, enabling PHS to support fax and voice-mail services and emerging multimedia applications such as high-speed Internet access and photo and video transmission.

PHS supports the handoff of calls from one microcell to the next during roaming. However, PHS goes a step farther than cellular by giving users the flexibility to make calls at home (just like conventional cordless phones), at school, in the office, while riding the subway, or while roaming through the streets. PHS also gives subscribers more security and complete privacy. And unlike cellular phones, PHS phones cannot be cloned for fraudulent use.

Another key advantage of PHS over cellular is cost—PHS can provide mobile communications more economically that cellular. Through its efficient microcell architecture and use of the public network, startup and expansion costs for operators are minimized. As a result, total per-subscriber costs tend to be much lower than with traditional cellular networks.

Because PHS is a “low tier” microcellular wireless network, it offers far greater capacity per dollar of infrastructure than existing cellular networks, which results in lower calling rates. In Japan, the cost of a 3-minute call using a PHS handset is comparable to the cost of making that same call on a public phone.

Handsets

Not only are PHS handsets extremely small and lightweight— almost half the size and weight of cellular handsets—but the battery life of PHS handsets is superior to that offered by cellular handsets. PHS phones output 10 to 20 milliwatts, whereas most cellular phones output between 1 and 5 watts. Whereas the typical cellular handset has a battery life of 3 hours talk time, the typical PHS handset has a battery life of 6 hours talk time.

Whereas the typical cellular handset has a battery life of 50 hours in standby mode, the typical PHS handset has a battery life of 200 hours in standby mode (more than a week). The low-power operation of PHS handsets is achieved through strict built-in power management and “sleep” functions in individual circuits.

Applications

There are a number of applications of PHS technology. In the area of mobile telecommunications, users can establish communications through public cell stations, which are installed throughout a serving area. PHS phones also can be used with a home base station as a residential cordless telephone at the Public Switched Telephone Network (PSTN) tariff.

When used in the local loop, PHS provides the means to access the PSTN in areas where conventional local loops— consisting of copper wire, optical fiber, or coaxial cable—are impractical or not available. PHS also can be adopted as a digital cordless PBX for office use, providing readily expandable, seamless communications throughout a large office building or campus.

Users carry PHS handsets with them and are no longer chained to their desks by their communications systems. As a digital system, PHS provides a level of voice quality not normally associated with a cordless telephone. In addition, the digital signal employed by PHS provides security for corporate communications, and the system’s microcell architecture can be reconfigured easily to accommodate increases or decreases in the number of users.

Another benefit of PHS is the ease and minimal expense with which the entire network can be dismantled and set up again in another facility if, for example, a business decides to relocate its offices. For personal use as a cordless telephone at home, PHS is a low-cost mobile solution that allows the customer to use a single handset at home and out of doors with a digital signal that provides improved voice quality for a cordless phone and enough capacity for data and fax transmissions that are increasingly a part of users’ home communications.

Network Architecture

The PHS radio interface offers four-channel Time Division Multiple Access with Time Division Duplexing (TDMA/TDD), which provides one control channel and three traffic channels for each cell station. The base station allocates channels dynamically and is not constrained by a frequency reuse scheme, thus deriving the maximum advantage of carrier-switched TDMA.

This means that PHS handsets communicating to a base station may all be on different carrier frequencies. The PHS system uses a microcell configuration that creates a radio zone with a 100- to 300-meter diameter. The base stations themselves are spaced a maximum of 500 meters apart. In urban areas, the microcell configuration is capable of supporting several million subscribers.

This configuration also makes possible smaller and lighter handsets and the more efficient reuse of radio spectrum to conserve frequency bands. In turn, this permits very low transmitter power consumption and, as a result, much longer handset talk times and standby times than are possible with cellular handsets.

A drawback of the lower operating power level is the smaller radius that a PHS base station can cover: only 100 to 300 meters, versus at least 1500 meters for cellular base stations. The extra power of cellular systems improves penetration of the signals into buildings, whereas PHS may require an extra base station inside some buildings. Another drawback of PHS is that the quality of reception can diminish significantly when mobile users are traveling at a rate greater than 15 miles per hour.

Since PHS uses the public network rather than dedicated facilities between microcells, the only service startup requirements are handsets, cell stations, a PHS server, and a database of services to support PHS network operation. With no separate transmission network needed for connecting cell stations and for call routing, carriers can introduce PHS service with little initial capital investment.

Service Features

PHS is a feature-rich service, giving Handyphone users access to a variety of call-handling features, including:

Call forwarding To a fixed line, to another PHS phone, or to a voice mail box.
Call waiting Alerts the subscriber of an incoming call.
Call hold Enables the subscriber to alternate between two calls.
Call barring Restricts any incoming local or international call.
Calling line identification (CLI) Displays the number of the incoming call, informing the subscriber of the caller’s identity.
Voice mail The subscriber receives recorded messages, even when the phone is busy or turned off.
Text messaging Enables the subscriber to send and receive text messages through the PHS phone.
International roaming Enables subscribers to use their PHS phones in another country but be billed by the service provider in their home country.

Depending on the implementation progress of the service provider, the following value-added data services also may be available to Handyphone users:

Virtual fax Enables subscribers to retrieve fax messages anywhere, have fax messages sent to a Handyphone, or have them redirected to any fax machine.
Fax By attaching the Handyphone to a laptop or desktop computer, subscribers can send and receive faxes anywhere.
E-mail/Internet access Allows subscribers to retrieve email from the Internet through the Handyphone.
Conference calls Enables subscribers to talk to as many as four other parties at the same time.
News, sports scores, and stock quotes Enables subscribers to obtain a variety of information on a real-time basis.

Many other types of services can be implemented over PHS. There is already the world’s first consumer-oriented videophone service in Japan. Kyocera Corp. offers a mobile phone able to transmit a caller’s image and voice simultaneously. Two color images are transmitted per second through a camera mounted on the top of the handset. The recipient can view the caller via a 2-inch active matrix liquid- crystal display (LCD). Since the transmission technology sends data at only 32 kbps, however, this makes for jerky video images.

While 32-kbps channels are now available in Japan, research is now under way to achieve a transmission rate of 64 kbps through the combined use of two channels. With this much capacity, PHS can be extended to a variety of other services in the future, including better-quality video.

In combination with a small, lightweight portable data terminal, PHS also may be used to realize the concept of “mobile network computing,” whereby users would access application software stored on the Internet. With the limited memory and disk storage capacity of the PHS terminals, the applications and associated programs would stay on the Internet, preventing the PHS devices from becoming overwhelmed.

Personal Digital Assistants

2010-11-12T17:39:00.001-08:00

Personal digital assistants (PDAs) are hand-held computers equipped with operating system and applications software. PDAs can be equipped with communications capabilities for short-text messaging, e-mail, news updates, Web surfing, voice mail, and Internet telephony. Today’s PDAs also can act as MP3 players, voice recorders, and digital cameras with the addition of multimedia modules.

Some PDAs can even accommodate a module that provides location information via the Global Positioning System (GPS). PDAs are intended for mobile users who require instant access to information regardless of their location at any given time. The Newton MessagePad, introduced by Apple Computer in 1993, was the first true PDA.

Trumpeted as a major milestone of the information age, the MessagePad was soon joined by similar products from such companies as Hewlett- Packard, Motorola, Sharp, and Sony. These early hand-held devices were hampered by poor performance, excessive weight, and unstable software. Without a wireless communications infrastructure, there was no compelling advantage of owning a PDA.

With the performance limitations largely corrected and the emergence of new wireless PCS—plus continuing advances in operating systems, connectivity options, and battery technology—PDAs are now well on the way toward fulfilling their potential.

Applications

Real estate agents, medical professionals, field service technicians, and delivery people are just a few of the people using PDAs. Real estate agents can use PDAs to conveniently browse through property listings at client locations. Health care professionals can use PDAs to improve their ability to access, collect, and record patient information at the point of care.

Numerous retailers and distributors can collect inventory data on the store and warehouse floor and later export tose data into a spreadsheet on a PC. Insurance agents, auditors, and inspectors can use PDAs to record data in the field and then instantly transfer those data to PCs and databases at the home office.

For professionals who tote around a laptop computer to give presentations with Microsoft PowerPoint, there is a module for the Springboard Visor that connects the device directly to digital projectors (or other VGAdisplays) with an interface cable. The user downloads the presentation material from a PC to the Visor and then taps an icon displayed on the Visor screen to start the 1024 × 768 resolution color presentation. The user can even control the presentation from anywhere in the room using the product’s infrared remote control.

PDA Components

A side from the case, PDA components include a screen, keypad, or other type of input device; an operating system; memory; and battery. Many PDAs can be outfitted with fax/modem cards and a docking station to facilitate direct connection to a PC or LAN for data transfers and file synchronization. Some PDAs, such as Palm Computing’s Palm VII, have a wireless capability that allows information retrieval from the Internet.

Of course, PDAs run numerous applications to help users stay organized and productive. Some PDAs have integral 56-kbps modems and serial ports that allow them to be attached via cable to other devices. Aunique PDAis Handspring’s Visor, which uses the Palm OS operating system.

What makes the Visor unique is that it is expandable via an external expansion slot called a Springboard. In addition to backup storage and flash storage modules, the slot lets users add software and hardware modules that completely change the function of the Visor. Springboard modules allow the Visor to become an MP3 player, pager, modem, GPS receiver, e-book, or video game device.

Display The biggest limitation of PDAs is the size of their screens. Visibility is greatly improved through the use of nonglare screens and backlighting, which aid viewing and entering information in any lighting condition. In a dim indoor environment, backlighting is a virtual necessity, but it drains the battery faster. Some PDAs offer user-controllable backlighting, while others let the user set a timer that shuts off the screen automatically after the unit has been idle for a specified period of time. Both features greatly extend battery life. Other PDAs, such as the Visor Prism, feature an active-matrix backlit display capable of displaying over 65,000 colors.

Keyboard Some PDAs have on-screen keyboards, but they are too small to permit touch typing. The use of a stylus speeds up text input and makes task selection easier. Of course, the instrument can be used for handwritten notes. The PDA’s handwriting-recognition capability enables the notes to be stored as text for use by various applications, such as a date book, address book, and to-do list. As an option, foldout full-size keyboards are available that attach to the PDA. They weigh only 8 ounces, making it much easier to respond to e-mail, compose memos, and take notes without having to lug around a laptop.

Operating Systems A PDA ’s operating system provides the foundation on which applications run. The operating system may offer handwriting recognition, for example, and include solutions for organizing and communicating information via fax or electronic mail, as well as the ability to integrate with Windows and Mac OS-based computers in enterprise environments.

The operating system also may include built-in support for a range of modems and third-party paging and cellular communication solutions. Because memory is limited in a PDA, usually between 2 and 64 MB, the operating system and the applications that run on it must be compact. Some operating systems come with useful utilities. There are utilities that set up direct connections between the PDA and desktop applications to transfer files between them via a cable or infrared connection.

A synchronization utility ensures that the user is working from the latest version of a file. Some operating systems offer tools called “intelligent agents” that automate routine tasks. An intelligent agent can be programmed to set up a connection to the Internet, for example, and check for e-mail. To activate this process, the user might only have to touch an icon on the PDA’s screen with a pen.

There are two major operating systems in use today— Microsoft’s Pocket PC platform and the Palm OS. Pocket PC’s predecessor, Windows CE, was too difficult to use and not powerful enough to draw users away from the popular Palm OS. But the Pocket PC’s redesigned interface overcomes most of Windows CE’s previous problems. The Pocket PC platform is a version of Windows that preserves the familiarity of the Windows-based desktop and integrates seamlessly with Outlook, Word, and Excel.

The platform includes a version of Internet Explorer for browsing the Web over a wireless connection or ordinary phone line and Windows Media Player for listening to digital music and watching digital videos. It also includes Microsoft Reader for reading e-books downloaded from the Internet. Palm OS is a more efficient operating system than Pocket PC. Consequently, it requires less processing power and less memory than equivalent products using the Pocket PC operating system.

Memory Although PDAs come with a base of applications built into ROM—usually a file manager, word processor, and scheduler—users can install other applications as well. New applications and data are stored in RAM. At a minimum, PDAs come with only 2 MB, while others offer up to 64 MB. When equipped with 2 MB of memory, the PDAcan store approximately 6000 addresses, 5 years of appointments, 1500 to-do items, and 1500 memos.

Some PDAs have a PC card (formerly PCMCIA) slot that can accommodate storage cards that are purchased separately. Even though many Pocket PC products come in higher memory configurations, an 8-MB Palm OS product can store as much or even more information than a 16-MB Pocket PC product with little performance degradation.

The better performance is due to the efficiencies of the Palm OS, which uses less memory and processing power than equivalent products based on Pocket PC. Since greater memory capacity increases the overall price of the product, vendors like Handspring believe that 8 MB offers the most utility at the most competitive price.

Power Many PDAs use ordinary AAA alkaline batteries. Manufacturers claim a battery life of 45 hours when users search for data 5 minutes out of every hour the unit is turned on. Of course, using the backlight display will drain the batteries much faster. Using the backlight will reduce battery life by about 22 percent. Other power sources commonly used with PDAs include an ac adapter and rechargeable lithium-ion battery.

The rechargeable battery offers more flexible power management in a smaller space. The components that operate the color screen increase the power draw from the battery. With AAA batteries, the user would have to replace them rather frequently. The rechargeable battery solution enhances the user’s experience by providing full power in a pocket-sized package. Lithium-ion rechargeable batteries offer 2 hours of continuous use.

Fax/Modems Some PDAs come with an external fax/modem to support basic messaging needs when hooked up to a telephone line. Others offer a PC card slot (formerly PCMCIA) that can accept not only fax/modems but also storage cards. With fax/modems, PDAusers can receive a fax from their office, annotate it, and fax it back with comments written on it in “electronic ink.”

There are wireless Ethernet modules available that allow the user to roam about the workplace or campus with secure connections, peer-to-peer links between devices, and highspeed access to the Internet, e-mail, and network resources. Transmissions of up to 11 Mbps are possible, but actual throughput is determined by the speed of the PDA’s processor.

The modules adhere to the IEEE 802.11b high-rate standard for wireless LANs and support 40- or 128-bit Wired-Equivalent Privacy (WEP) encryption. Transmission ranges of up to 1000 feet (300 meters) in open environments and 300 feet (90 meters) in office environments are supported.

Cradle A cradle allows the PDAto connect to a desktop PC via a standard serial cable or USB cable. The user simply drops the PDAinto the cradle and presses a button to automatically synchronize desktop files with those held in the PDA. An alternative to cable is an infrared (IR) connection.

With an IR-enabled PDA, users not only can swap and synchronize files with a PC but also can beam business cards, phone lists, memos, and add-on applications to other IRenabled PDAs. IR-enabled PDAs also can use third-party beaming applications with IR-enabled phones, printers, and other devices.

Improvements in technology and the availability of wireless communications services, including PCS, overcome many of the limitations of early PDAproducts, making today’s handheld devices very attractive to mobile professionals. In the process, PDAs are finding acceptance beyond vertical markets and finally becoming popular among consumers, particularly those looking for an alternative to notebook computers and younger people who want a versatile device from which they also can play MP3 music files and games as well as read e-books.

Personal Communications Services

2010-11-12T17:34:00.001-08:00

Personal Communications Services (PCS) is a set of wireless communication services personalized to the individual. Subscribers can tailor their service package to include only the services they want, which may include stock quotes, sports scores, headline news, voice mail, e-mail and fax notification, and caller ID. The service offers full roaming capability, allowing anywhere-to-anywhere communication.

Unlike many existing cellular networks, PCS is a completely digital service. The digital nature of PCS allows antennas, receivers, and transmitters to be smaller. It also allows for the simultaneous transmission/reception of data and voice with no performance penalty. Eventually, PCS will overtake analog cellular technology as the preferred method of wireless communication. Several technologies are being used to implement PCS.

In Europe, the underlying digital technology for Personal Communication Networks (PCNs) is Global System for Mobile (GSM) Telecommunications, where it has been assigned the 1800-MHz frequency band. GSM has been adapted for operation at 1900 MHz for PCS in the United States (i.e., PCS 1900). Other versions of GSM are employed to provide PCS services in other countries, such as the Personal Handyphone System (PHS) in Japan.

Many service providers in the United States have standardized their PCS networks on Code Division Multiple Access (CDMA) or Time Division Multiple Access (TDMA) digital technology.

The PCS Network

A typical PCS network operates around a system of microcells— smaller versions of a cellular network’s cell sites— each equipped with a base station transceiver. The microcell transceivers require less power to operate but cover a more limited range. The base stations used in the microcells can even be placed indoors, allowing seamless coverage as the subscriber walks into and out of buildings.

Similar to packet radio networks today, terminal devices stay connected to the network even when not in use, allowing the network to locate an individual within the network via the nearest microcell and routing calls and messages directly to the subscriber’s location. For a “follow me” service, which incorporates more than one device, a subscriber may be required to turn on a pager, for example, to receive messages on that device.

If the subscriber receives a phone call while the pager is on, the network may store the call, take a message, or send the call to a personal voice-mail system and simultaneously page the subscriber. In this way, PCS allows the concept of universal messaging to be fully realized. Currently, cellular switching systems operate separately from the Public Switched Telephone Network (PSTN).

When cellular subscribers call a landline phone (and vice versa), the two systems are interconnected to complete the communications circuit. Many PCS services are supported on the same switches that handle calls over the wire-line network, with the only distinction between a wireless and wire-line call being the medium at each end of the circuit.

In some places, wireless PCS and cable television (CATV) are already integrated in a unified CDMA-based architecture called “PCS over cable.” The use of CATV allows PCS to reach more potential subscribers with a lower startup costs for service providers.

Broadband and Narrowband

There are two technically distinct types of PCS: narrowband and broadband, each of which operates on a specific part of the radio spectrum and has unique characteristics. Narrowband PCS is intended for two-way paging and other types of communications that handle small bursts of data. These services have been assigned to the 900-MHz frequency range, specifically, 901 to 912, 930 to 931, and 940 to 941 MHz.

Broadband PCS is intended for more sophisticated data services. These types of services have been assigned a frequency range of 1850 to 1990 MHz. Narrowband PCS and broadband PCS license ownerships have been determined by public auctions conducted by the Federal Communications Commission (FCC). PCS service areas are divided into 51 regional service areas, which are subdivided into a total of 492 metropolitan areas.

There is competition in each service area by at least two service providers. There are 10 national service providers plus 6 regional providers in each of 5 multistate regions called “major trading areas.” An unlicensed portion of the PCS spectrum has been allocated from 1890 to 1930 MHz. This service is designed to allow unlicensed operation of short-distance—typically indoor or campus-oriented environments—voice and data services provided by wireless LANs and wireless Public Branch Exchanges (PBXs).

One of the largest PCS networks is operated by Sprint PCS. At year end 2001, the company’s CDMA-based wireless network served close to 13 million customers, making it the fourth largest wireless carrier. In addition to offering voice services from 300 major metropolitan markets, including more than 4000 cities and communities in the United States, the company leads the wireless industry in the number of wireless Web users on its Internet-ready phones and devices.

In addition, users may shop online at Amazon.com from their Internet-ready Sprint PCS phones. The service supports two-way transactional electronic commerce services to provide users with easy and convenient shopping on the Internet. Users also easily access the Sprint PCS Wireless Web to check e-mail, news, stock portfolios, or flight schedules.

The service offers the ability to customize and receive important news, receive e-mail and information updates from Yahoo, as well as dial into a corporate intranet or the Internet using a Sprint PCS phone in place of a modem connected to a laptop, PDA, or other handheld computing device.

Migration to 3G

PCS service providers are in the process of migrating their wireless networks to the global third generation (3G) framework. In the case of PCS based on CDMA, this entails a multiphase rollout of new technology that will increase the network’s capacity for both voice and data.

The first phase of deployment will be to migrate to a Code Division Multiple Access 2000 (CDMA 2000) network, which will double the PCS network’s capacity for voice communications, increase data transmission speeds from 14.4 to 144 kbps, and lower handset battery consumption.

In early 2003, PCS service providers will move to the second stage of their transition to 3G and offer data speeds of up to 384 kbps. By late 2003, data transmission speeds will reach up to 2.4 Mbps, and in early 2004, transmission speeds for voice and data are expected to hit between 3 and 5 Mbps.

The popularity of PCS is bringing about a variety of new mobile and portable devices such as small, lightweight telephone handsets that work at home, in the office, or on the street; advanced “smart” paging devices; and wireless electronic mail and other Internet-based services. PCS services are available in all regions of the United States.

Most of the smaller PCS networks are now interconnected to the nationwide PCS networks, providing users with extensive roaming coverage without having to switch to analog cellular on a dual-mode handset. At this writing, momentum toward 3G networks has stalled. Questions about how much demand there is for 3G services and delays in 3G network implementations are causing many PCS service providers to rethink their transition timetable.

Personal Air Communications Technology

2010-11-12T17:33:00.001-08:00

Personal Air Communications Technology (pACT) is a wireless two-way messaging and paging technology that is offered as an alternative to wireless Internet Protocol (IP), also known as Cellular Digital Packet Data (CDPD). The pACT specification, released in 1995, was developed to enable compact, inexpensive devices to access low-cost, highcapacity network infrastructures.

The protocol enhances one-way paging, response paging, two-way paging, voice paging, telemetry, and two-way messaging applications. The pACT protocol thus addresses the demands of a growing market for narrowband PCS. Despite huge investments in spectrum for narrowband PCS, some U.S. paging carriers are already running short of bandwidth. This situation has prompted them to look for ways to add capacity to their networks.

In major U.S. cities, the solution has been to make better use of existing spectrum. pACT supports two-way messaging and paging applications while still retaining all the strengths of one-way paging services, including long battery life, good in-building reception, and ubiquitous coverage. pACT also provides carriers with the ability to substantially increase system capacity by more efficiently utilizing spectrum, thereby allowing for more cost-effective paging and messaging services.

Its cellular-like network design enables carriers to take advantage of capacity gains through frequency reuse, a fundamental difference from other two-way systems. The difference between wireless IP and pACT is that the former is TCP/IP-centric, whereas the latter is User Datagram Protocol/Internet Protocol (UDP/IP)–centric.

While wireless IP compresses the standard 40-byte TCP/IP header to an average of 3 bytes to conserve bandwidth, pACT compresses the header to only 1 byte. The greater compression is important for providing a short alphanumeric messaging service, especially when the message body is roughly the same size as the header. Consequently, the maximum number of subscribers that can be supported by the system is constrained not by protocol efficiency but by service traffic.

Applications

Two-way wireless messaging is working its way into a myriad of user applications where one-way messaging is no longer adequate. These are applications where time is of the essence, and guaranteed message delivery is critical. pACT uses the same upper layers of the protocol stack as wireless IP, making it suitable for a broad range of messaging applications, including two-way-paging, e-mail, fleet dispatch, telemetry, transaction processing (e.g., point-of-sale credit card authorizations), and voice messaging.

Since pACT is based on the IP, it provides wireless network users with access to other IP-based networks such as corporate local area networks (LANs) and the Internet from remote locations. Network Capacity Narrowband PCS and two-way protocols such as pACT give the paging industry new ways to increase the capacity of one-way paging systems, which introduce opportunities for providing new and enhanced services.

Like traditional mobile telephony systems, pACT increases capacity by reusing frequencies—theoretically providing unlimited capacity. Given higher airlink speeds (8 kbps) and knowing a subscriber’s exact location, operators can increase capacity in a large zone by 100 to 200 times and even more in networks that are made up of several zones. While one-way paging over a two-way network offers no real benefits to subscribers, the benefits to operators are substantial.

First, two-way networks enable paging devices to acknowledge that a message has been received. With this capability, operators can offer subscribers guaranteed delivery, which can result in competitive advantage. The second benefit to operators is that they do not have to broadcast a message via every transmitter in the network to reach an intended recipient.

With a two-way network, the exact location of each subscriber device is known because the devices register automatically as they move through the network. Since messages are sent solely via the transmitter that is closest to the subscriber, a great deal of network capacity is freed. This means that all other transmitters in the network can be used simultaneously to serve other subscribers.

Service Enhancement The two-way pACT architecture affects more than capacity: It also enables providers to enhance services, as well as to provide completely new services and applications. For example, paging devices that contain a transmitter are able to send information back to the network, to someone else in the network, or to any other network. The two-way paging and messaging paradigm provides five levels of acknowledgment:

System acknowledgment The paging device acknowledges receipt of an error-free message. Atransparent Link Layer acknowledgment between the device and the network enables guaranteed delivery service. The network stores and retransmits messages at periodic intervals that pagers have not acknowledged.
Message read When a recipient reads a message, the paging device transmits a “message read” acknowledgment back to the host system or to the originator of the message.
Canned messages The paging device contains several ready-to-use responses such as “Yes” or “No” that recipients can use when they reply to an inquiry.
Multiple choice The originator of a message defines several possible responses to accompany his or her message. To reply, the recipient selects the most appropriate response.
Editing capabilities Some devices may be used to create messages. Editing capabilities vary from device to device. Some devices are managed by a few simple keys and provide only minor editing capabilities, while others such as portable computers may contain full-feature keyboards.

Like wireless IP, pACT provides secure service—including encryption and authentication—to ensure that messages are delivered solely to intended subscribers.

System Overview

The pACT system is built from several flexible modules that can be combined and configured in different ways to meet specific operator demands. Because the pACT network is based on the IP, operators and application providers can take full advantage of existing applications, application programming interfaces (APIs), and other development tools. With pACT, a single 50-kHz channel may accommodate up to three individual radiofrequency (RF) carriers. Each base station is assigned a particular 12.5-kHz channel.

pACT Data Base Stations The pACT data base stations (PDBS) are located at the cell site and relay data between subscriber devices and the serving pACT data intermediate system (PDIS). Typically, the PDBSs are connected to the serving PDIS switch via a Frame Relay network. Cellular radio system design and roaming techniques enable pACT to determine which base station is closest to a subscriber device each time communication takes place between the device and the network. The mobile terminals determine cell handoff based on signal-strength measurements implemented by the base stations.

pACT Data Intermediate System The PDIS acts as the central switching site, routing data to and from the appropriate base stations. It also maintains routing information for each subscriber device in the network. There are two versions of the PDIS: the home PDIS and the serving PDIS. Besides switching data packets, the home PDIS maintains a location directory and provides a forwarding service and subscriber authentication.

Every subscriber is registered in a home PDIS database. The serving PDIS provides message forwarding, a registration directory, and readdress services. Other services or functions are multicast, broadcast, unicast, airlink encryption, header compression (to minimize airlink use), data segmentation, frame sequencing, and network management. The serving PDIS is connected to the home PDIS switch.

If necessary, the two switches may be located on the same hardware platform. Various configurations of computer processor power and memory are available for the PDIS, depending on requirements for computing capacity and on how the requirements relate to traffic load and the number of subscribers in the network. More computing capacity may be added easily if necessary.

Message Center The fixed entry point into the pACT network is provided by one or more message centers (MCs) that initiate, provision, and connect pACT services to private and public networks, including corporate intranets and the PSTN, respectively. Every message passes through the message center, whose functionality and applications vary according to network operator requirements.

The core of the message center is the message store, which handles virtually any data type and makes APIs accessible for building various applications, such as interactive voice response (IVR) and voice or fax mail. The message store also provides functions for operation and maintenance, system monitoring, and event/alarm handling.

Any of the message center’s databases can be queried via the Structured Query Language (SQL). The message center also supports virtually any protocol. Typical protocols are the IP, Telocator Alphanumeric Protocol (TAP), Telocator Network Paging Protocol (TNPP), and X.400 (the ITU-T standard for message handling services).

Network Management System

The pACT network management system (NMS) gives operators full control of every component in a pACT network. Through the NMS, each base station is provided with a set of radio resource management (RRM) parameters that are used to control traffic and maintain links to the network, as well as to give instructions to mobile terminals that access the channel.

The NMS supports the Common Management Information Protocol (CMIP) and the Simple Network Management Protocol (SNMP). The NMS contains a database component that permanently stores parameters, configuration data, and historical records of traps and performance data. ApA CT network may contain more than one NMS, allowing responsibility to be passed across time zones to other operators, ensuring 24-hour monitoring and control.

Customer Activation System The pACT Customer Activation System (CAS) enables customer service representatives to manage customer accounts and to dynamically activate pACT-related services for customers. Customer accounts are of two types: individual and business, where individual accounts are for single subscribers and business accounts are for multiple subscribers.

pACT End System (Mobile Terminals) Mobile terminals range from simple pagers to sophisticated two-way messaging devices such as PDAs or palmtop computers with wireless modems. When not being used to send messages, mobile terminals periodically check the designated forward channel for incoming messages; otherwise, they are usually in sleep mode to conserve battery life.

pACT System Protocol Stack The pACT protocol stack is based on the concepts and principles of the ITU-X.200 and ITU-X.210 reference models, as well as service conventions for Open Systems Interconnection (OSI). The Limited Size Messaging (LSM) protocol provides the functionality of a simple e-mail application protocol, such as the Simple Mail Transfer Protocol (SMTP), but is optimized for low-bandwidth channels so that unnecessary overhead over the airlink is minimized.

In addition, the LSM protocol provides a platform for providing true two-way messaging and data communication services. Examples of services are embedded response messaging for simple pager devices, true twoway e-mail connectivity, and multicast and broadcast messaging. pACT’s subnetwork convergence layer provides a new approach to encryption.

To ensure that airlink bandwidth is not spent on resynchronizing the encryption engines, pACT devices may employ a technique that automatically resynchronizes the engines, even when the underlying layers fail to deliver a packet. This technique is important because it provides a mechanism by which multicast and broadcast services may be encrypted.

The CDPD Link Layer is optimized for duplex, whereas pACT uses two-way simplex. The pACT Mobile Data Link Layer Protocol (MDLP) is an enhanced version of the link access procedure on the D-channel (LAPD) (i.e., ITU Q.920) that allows subscriber devices to adopt strategies for automatically resetting the link and saving power.

pACT Airlink Interface The pACT backbone network is similar to a CDPD network. The main differences between the two involve functionality—mostly for extending battery life in subscriber devices—and features such as group messaging, broadcast, and unicast. The pACT protocol shortens and reduces the number of transmissions and contains an efficient sleep mode for conserving battery power.

As an alternative to wireless IP, also known as CDPD, Personal Air Communications Technology (pACT) supports various paging and messaging applications while providing more efficient use of limited spectrum. This allows wireless carriers to stay competitive, even when they cannot easily add more capacity to their networks. Since pACT is based on the IP, wireless network users can access other IP-based networks such as corporate LANs and the Internet from remote locations. With integral authentication and encryption, data are protected as they traverse the pACT network.

Personal Access Communications Systems

2010-11-12T17:32:00.001-08:00

Personal Access Communications Systems (PACS) is a standard adopted by ANSI for Personal Communication Services (PCS). Adopted in June 1995, PACS provides an approach for implementing PCS in North America that is fully compatible with the local exchange telephone network and interoperable with existing cellular systems.

Based on the Personal Handyphone System (PHS) developed in Japan and the Wireless Access Communications System (WACS) developed by Bellcore (now known as Telcordia Technologies), PACS is designed to support mobile and fixed applications in the 1900-MHz frequency range. It promises low installation and operating costs while providing very-high-quality voice and data services.

In the United States, trials of PACS equipment began in 1995, and equipment rollout began in 1996. Most of the standards—including up-banded versions of CDMA, TDMA, and GSM—look like cellular systems in that they have high transmit powers and receivers designed for the large delay spreads of the macrocellular environment and typically use low-bit-rate voice coders (vocoders).

PACS fills the niche between these classes of systems, providing high-quality services, high data capability, and high user density in indoor and outdoor microcellular environments. PACS equipment is simpler and less costly than macrocellular systems yet more robust than indoor systems. PACS capabilities include pedestrian- and vehicularspeed mobility, data services, and licensed and unlicensed spectrum systems, as well as simplified network provisioning, maintenance, and administration.

The key features of PACS are summarized as follows:

Voice and data services are comparable in quality, reliability, and security with wire-line alternatives.
Systems are optimized to provide service to the in-building, pedestrian, and city traffic operating environments.
It is most cost-effective to serve high-density traffic areas.
Small, inexpensive line-powered radios provide for unobtrusive pole or wall mounting.
There is low-complexity per-circuit signal processing.
Low transmit power and efficient sleep mode require only small batteries to power portable subscriber units for hours of talk time and multiple days of standby time.

Like the Personal Handyphone System (PHS), PACS uses 32-kbps Adaptive Differential Pulse Code Modulation (ADPCM) waveform encoding, which provides near landline voice quality. ADPCM has demonstrated a high degree of tolerance to the cascading of vocoders, as experienced when a mobile subscriber calls a voice-mail system and the mailbox owner retrieves the message from a mobile phone. With other mobile technologies, the playback quality is noticeably diminished.

With PACS, it is very clear. Similarly, the compounding of delays in mobile to PCS through satellite calls—a routine situation in Alaska and in many developing countries—can be troublesome. PACS provides extremely low delay. The low complexity and transmit power of PACS yield limited cell sizes, which makes it well suited for urban and suburban applications where user density is high.

Antennas can be installed inconspicuously, piggybacking on existing structures. This avoids the high costs and delays associated with obtaining permits for the construction of high towers.

Applications

Wireless local loop, pedestrian venues, commuting routes, and indoor wireless are typical PACS applications. Additionally, PACS is designed to offer high-capacity, superior voice quality and Integrated Services Digital Network (ISDN) data services. Interoperability with ISDN is provided by aggregating two 32-kbps time slots to form a single higher-speed 64-kbps channel. A64-kbps channel also can support 28.8-kbps voice-band data using existing modems.

PACS also can be used for providing wireless access to the Internet. The packet data communications capabilities defined in the PACS standards, together with the ability to aggregate multiple 32-kbps channels, make it possible for users to access the Internet from their PCs equipped with suitable wireless modems at speeds of up to 200 kbps. When using the packet mode of PACS for Internet traffic, radio channels are not dedicated to users while they are on active Internet sessions, which can be very long.

Rather, radio resources are used only when data are actually being sent or received, resulting in very efficient operation and minimally impacting the capacity of the PACS network to support voice communications. PACS was designed to support the full range of advanced intelligent network (AIN) services, including custom calling features and personal mobility. As new AIN features are developed, the PACS-compliant technology will evolve to facilitate incorporation of the new services.

The market for PCS is very competitive. Already PCS is exerting downward price pressure on traditional analog cellular services where the two compete side by side. PACS enables PCS operators to differentiate their offerings through digital voice clarity, high-bit-rate data communications, and advanced intelligent network services—all in a lightweight handset. Moreover, the cost savings and ease of use associated with PACS make it very economical for residential and business environments compared to competitive high-powered wide area systems.

Peer-to-peer Network

2010-11-12T17:31:00.003-08:00

In a peer-to-peer network, computers are linked together for resource sharing. If there are only two computers to link together, networking can be done with a Category 5 crossover cable that plugs into the RJ45 jack of the network interface card (NIC) on each computer. If the computers do not have NICs, they can be connected with either a serial or parallel cable.

Once connected, the two computers function as if they were on a local area network (LAN), and each computer can access the resources of the other. If three or more computers must be connected, a wiring hub is required. The peer network can be extended to portable devices, including desktop and notebook computers and personal digital assistants (PDAs), through the use of wireless access points.

The access point connects to the LAN through a hub or switch via Category 5 cabling, just like any other device on the wired network. The access point establishes the wireless link to one or more client devices, which are equipped with a wireless card. The wireless devices operate in either the 2.4-GHz band for 11 Mbps or the 5-GHz band for 54 Mbps.

Newer access points have slots for wireless cards of both frequency bands, allowing users to protect investments in 2.4-GHz equipment while migrating to the higher speeds offered by 5-GHz equipment. Regardless of exactly how the computers are interconnected, wired or wireless, each is an equal or “peer” and can share the files and peripherals of the others.

For a small business doing routine word processing, spreadsheets, and accounting, this type of network is the low-cost solution to sharing resources like files, applications, and peripherals. Multiple computers can even share an external cable or Digital Subscriber Line (DSL) modem, allowing them to access the Internet at the same time.

Networking with Windows

Windows 95/98 and Windows NT/2000 are often used for peerto- peer networking. In addition to peer-to-peer network access, both provide network administration features and memory management facilities, support the same networking protocols— including the Transmission Control Protocol/Internet Protocol (TCP/IP) for accessing intranets, virtual private networks (VPNs), and the public Internet—and provide such options as dial-up networking and fax routing.

One difference between the two operating systems is that in Windows 95/98 the networking configuration must be established manually, whereas in Windows NT/2000 the networking configuration is part of the initial program installation, on the assumption that NT/2000 will be used in a network.

Although Windows 95/98 is good for peer-to-peer networking, Windows NT/2000 is more suited for larger client-server networks. Windows supports Ethernet, Token Ring, Asynchronous Transfer Mode (ATM), and Fiber Distributed Data Interface (FDDI) data-frame types. Ethernet is typically the least expensive network to implement.

The NICs can cost as little as $20 each, and a five-port hub can cost as little as $40. Category 5 cabling usually costs less than 50 cents per foot in 100-foot lengths with the RJ45 connectors already attached at each end. Snap-together wall plate kits cost about $6 each.

If wireless connections are part of the peer network, the wireless NICs cost between $170 and $300, depending on whether the 2.4- or 5-GHz band is used. Access points can cost as little as $199 for 2.4-GHz units and $299 for 5-GHz units. Enterprise class versions cost quite a bit more.

Configuration Details

When setting up a peer-to-peer network with Windows 95/98, each computer must be configured individually. After installing an NIC and booting the computer, Windows will recognize the new hardware and automatically install the appropriate network-card drivers. If the drivers are not already available on the system, Windows will prompt the user to insert the manufacturer’s disk containing the drivers, and they will be installed automatically.

Next, the user must select the client type. If a Microsoft peer-to-peer network is being created, the user must add “Client for Microsoft Networks” as the primary network logon. Since the main advantage of networking computers is resource sharing, it is important to enable the sharing of both printers and files. The user does this by clicking on the “File and Print Sharing” button and choosing one or both of these capabilities.

Through file and printer sharing, each workstation becomes a potential server. Identification and security are the next steps in the configuration process. From the “Identification” tab of the dialog box, the user must select a unique name for the computer and the workgroup to which it belongs, as well as a brief description of the computer. When others use Network Neighborhood to browse the network, they will see the menu trees of all active computers on the network.

From the “Access Control” tab of the dialog box, the user selects the security type. For a small peer-to-peer network, share-level access is adequate. This allows printers, hard drives, directories, and other resources to be shared and enables the user to establish password access for each of these resources.

In addition, read-only access allows users to view (not modify) a file or directory. To allow a printer to be shared, for example, the user right-clicks on the printer icon in the Control Panel and selects “Sharing” from the drop-down list. Next, the user clicks on the “Shared As” radio button and enters a unique name for the printer.

If desired, this resource can be given a password as well. When another computer tries to access the printer, the user will be prompted to enter a password. If a password is not necessary, the password field is left blank. Another security option in the “Access Control” tab is user-level access, which is used to limit resource access by user name.

This function eliminates the need to remember passwords for each shared resource. Each user simply logs onto the network with a unique name and password; the network administrator governs who can do what on the network. However, this requires the computers to be part of a larger network with a central server—perhaps running Windows NT/2000 server—that maintains the accesscontrol list for the whole network.

Since Windows 95/98 and Windows NT/2000 workstations support the same protocols, Windows 95/98 computers can participate in a Windows NT/2000 server domain. Peer services can be combined with standard client-server networking.

For example, if a Windows 95/98 computer is a member of a Windows NT/2000 network and has a color printer to share, the resource “owner” can share that printer with other computers on the network. The server’s access-control list determines who is eligible to share resources. Once the networking infrastructure is in place, the NIC of each computer is individually connected to a hub with Category 5 cable or wirelessly via the access point.

This cable has connectors on each end that insert into the RJ45 jacks of the hub and NICs. For small networks, the hub usually will be manageable with the Simple Network Management Protocol (SNMP), so no additional software is installed. Once the computers are properly configured and connected to the hub, the network is operational.

Peer-to-peer networking is an inexpensive way for small companies and households to share resources among a small group of computers. This type of network provides most of the same functions as the traditional client-server network, including the ability to run network versions of popular software packages.

Peer-to-peer networks also are easy to install. Under ideal conditions, installation of the cards, software, hub, and cabling for five users would take only a few hours. Wireless links provide the advantage of mobility within the home or office, allowing a notebook to be used in any room.

PCS 1900

2010-11-12T17:31:00.001-08:00

PCS 1900 is the American National Standards Institute (ANSI) radio standard for 1900-MHz Personal Communication Service (PCS) in the United States. Also known as GSM 1900, it is compatible with the Global System for Mobile (GSM) communications, an international standard adopted by 404 networks supporting 538 million subscribers in 171 countries as of mid- 2001.

Network operators aligned to the GSM standard have 35 percent of the world’s wireless market. PCS 1900 can be implemented with either Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA) technology. TDMA-based technology enjoys an initial cost advantage over rival technology CDMAequipment because suppliers making TDMAinfrastructure equipment and handsets have already reached economies of scale.

In contrast, CDMAequipment is still in its first generation and therefore is generally more expensive. The CDMA(IS-95) standard has been chosen by about half of all the PCS licensees in the United States, giving it the lead in the total number of potential subscribers. However, the first operational PCS networks have been using PCS 1900 as their standard mainly because of the maturity of the GSM-based technology.

Although similar in appearance to analog cellular service, PCS 1900 is based on digital technology. As such, PCS 1900 provides better voice quality, broader coverage, and a richer feature set. In addition to improved voice quality, fax and data transmissions are more reliable. Laptop computer users can connect to the handset with a Personal Computer Memory Card International Association (PCMCIA) card and send fax and data transmissions at higher speeds with less chance of error.

Architecture

The PCS 1900 system architecture consists of the following major components:

Switching system Controls call processing and subscriberrelated functions.
Base station Performs radio-related functions.
Mobile station The end-user device that supports voice and data communications as well as short message services.
Operation and support system (OSS) Supports the operation and maintenance activities of the network.

The switching system for PCS 1900 service contains the following functional elements:

Mobile Switching Center (MSC) Performs the telephony switching functions for the network. It controls calls to and from other telephone and data communications networks such as Public Switched Telephone Networks (PSTN), Integrated Services Digital Networks (ISDN), Public Land Mobile Radio Services (PLMRS) networks, Public Data Networks (PDN), and various private networks.
Visitor Location Register (VLR) Adatabase that contains all temporary subscriber information needed by the MSC to serve visiting subscribers.
Home Location Register (HLR) Adatabase for storing and managing subscriptions. It contains all permanent subscriber information, including the subscriber’s service profile, location information, and activity status.
Authentication Center (AC) Provides authentication and encryption parameters that verify the user’s identity and ensure the confidentiality of each call. This functionality protects network operators from common types of fraud found in the cellular industry today.
Message Center (MC) Supports numerous types of messaging services, for example, voice mail, facsimile, and e-mail.

Advanced Services and Features

Like GSM, PCS 1900’s digital orientation makes possible several advanced services and features that are not efficiently and economically supported in analog cellular networks. Among them are:

Short Message Service - Enables alphanumeric messages up to 160 characters to be sent to and from PCS 1900–compatible handsets. Short Message Service applications include two-way point-to-point messaging, confirmed message delivery, cell-based messaging, and voice-mail alert. These messaging and paging capabilities create a broad array of potential new revenue-generating opportunities for carriers.
Voice Mail - The PCS 1900 network provides one central voice-mail box for both wired and wireless service. In addition, the voice-mail alert feature ensures that subscribers do not miss important messages.
Personal Call Management - Offers subscribers a single telephone number for all their physical telecommunication devices. For example, a single number can be assigned for home and mobile use or office and mobile use. This allows subscribers to receive all calls regardless of their physical location.
Data Applications - Wireless data applications that can be supported by PCS 1900 networks include Internet access, electronic commerce, and fax transmission.

Smart Cards

The PCS 1900 standard supports the smart card, which provides similar features as GSM’s Subscriber Identity Module (SIM). The size of a credit card, smart cards contain embedded computer chips with user-profile information.

By removing the smart card from one PCS 1900 phone and inserting it into another PCS 1900 phone, the user is able to receive calls at that phone, make calls from that phone, or receive other subscribed services such as wireless Internet access. The handsets cannot be used to place calls (except 911 emergency calls) until the subscriber inserts the smart card and enters a personal identification number (PIN).

The profile information stored in the smart card also enables international roaming. When traveling in the United States, international GSM customers will be able to rent handsets, insert their SIM, and access their services as if they are back home. By the same token, when U.S. subscribers travel internationally to cities with compatible networks and mutual roaming agreements, they only need to take their smart card with them to access the services they subscribed to back home via the local GSM network.

Like SIMs, smart cards also provide storage for features such as frequently called numbers and short messages. Smart cards also include the AT command-set extensions, which integrate computing applications with cellular data communications. In the future, smart cards and PCS 1900 technology also will link subscribers to applications in electronic commerce, banking, and health care.

PCS 1900 is a frequency-adapted version of GSM that operates at 1800 MHz in Europe and elsewhere. While GSM looks to be a perennial third in North America digital markets, this is mainly because the technology has not been adopted for use in cellular 800-MHz frequencies. Otherwise, PCS 1900 and GSM are similar in all other respects, including the network architecture and types of services supported.

An advantage U.S. carriers have in supporting the PCS 1900 standard is that it is interoperable with the worldwide GSM standard, which means that users can roam globally. GSM phones are available in either dual-band (900/1900 MHz) or triband (900/1800/1900 MHz) models, enabling their use in countries with different frequency bands for GSM services.

Paging

2010-11-09T20:54:00.000-08:00

Paging is a wireless service that provides one- or two-way messaging to give mobile users continuous accessibility to family, friends, and business colleagues while they are away from their telephones. Typically, the mobile user carries a palmsized device (the pager or some other portable device with a paging capability) that has a unique identification number.

The calling party inputs this number, usually through the Public Switched Telephone Network (PSTN), to the paging system, which then signals the pager to alert the called party. Alternatively, callback numbers and short-text messages can be sent to pagers via messaging software installed on a PC or input into forms accessed on the Web for delivery via an Internet gateway.

Regardless of delivery method, the called party receives an audio or visual notification of the call, which includes a display of the phone number to call back. If the pager has an alphanumeric capability, messages may be displayed on the pager’s screen.

The pioneer of wireless telecommunications is Al Gross. In 1938, the Canadian inventor developed the walkie-talkie. In 1948, he pioneered Citizens’ Band (CB) radio. In 1949, he invented the pager from radio technology he used for blowing up bridges via remote control during World War II. His first attempt to sell pagers to doctors and nurses in 1960 failed because nurses did not want to disturb patients and doctors did not want to disturb their golf games.

Gross’s ideas were so far advanced that most of his patents expired before the technology could catch up to make his inventions a reality. As a result, he did not make much money. Had he been born 35 years later, he could have capitalized on his ideas to become far wealthier than Bill Gates at Microsoft.

There are many applications for paging. Among the most popular are:

Mobile messaging Allows messages to be sent to mobile workers. They can respond with confirmation or a request for additional instructions.
Data dispatch Allows managers to schedule work appointments for mobile workers. When they activate their pagers each morning, their itinerary will be waiting for them.
Single-key callback Allows the user to read a message and respond instantly with a predefined stored message that is selected with a single key.

Some message paging services work with text messaging software programs, allowing users to send messages from their desktop or notebook computers to individuals or groups. This kind of software also keeps a log of all messaging activity. This method also offers privacy, since messages do not have to go through an operator before delivery to the recipient.

Several types of paging services are available.

Selective Operator-Assisted Voice Paging Early paging systems were nonselective and operator-assisted. Operators at a central control facility received voice input messages, which were taped as they came in. After an interval of time—15 minutes or so—these messages were then broadcast and received by all the paging system subscribers. This meant that subscribers had to tune in at appointed times and listen to all messages broadcast to see if there were any messages for them. Not only did this method waste airtime, it also was inconvenient and labor-intensive and offered no privacy.

These disadvantages were overcome with the introduction of address encoders at the central control facility and associated decoders in the pagers. Each pager was given a unique address code. Messages intended for a particular called party were input to the system preceded by this address. In this way, only the party addressed was alerted to switch on his or her pager to retrieve messages.

With selective paging, tone-only alert paging became possible. The called party was alerted by a beep tone to call the operator or a prearranged home or office number to have the message read back.

Automatic Paging Traditionally, an operator was always needed either to send the paging signal or to play back or relay messages for the called party. With automatic paging, a telephone number is assigned to each pager, and the paging terminal can automatically signal for voice input, if any, from the calling party, after which it will automatically page the called party with the address code and relay the input voice message.

Tone and Numeric Paging Voice messages take up a lot of airtime, and as the paging market expands, frequency overcrowding becomes a potentially serious problem. Tone-only alert paging saves on airtime usage but has the disadvantage that the alerted subscriber knows only that he or she has to call certain prearranged numbers, depending on the kind of alert tone received.

With the introduction of numeric display pagers in the mid-1980s, the alert tone is followed by a display of a telephone number to call back or a coded message. This method resulted in great savings in airtime usage because it was no longer necessary to add a voice message after the alert tone. This is still the most popular form of paging.

Alphanumeric Paging Alphanumeric pagers display text or numeric messages entered by the calling party or operator using a modem-equipped computer or a custom page-entry device designed to enter short-text messages. Although alphanumeric pagers have captured a relatively small market in recent years, the introduction of value-added services that include news, stock quotes, sports scores, traffic bulletins, and other specialized information services has heated up the market for such devices.

Ideographic Paging Pagers capable of displaying different ideographic languages—Chinese, Japanese, and others— are also available. The particular language supported is determined by the firmware (computer program) installed in the pager and in the page-entry device. The pager is similar to that used in alphanumeric display paging.

Paging System Components

The key components of a paging system include an input source, the existing wireline telephone network, the paging encoding and transmitter control equipment, and the pager itself.

Input Source A page can be entered from a phone, a computer with modem, or other type of desktop page-entry device; a personal digital assistant (PDA); or an operator who takes a phone-in message and enters it on behalf of the caller. Various forms posted on the Web also can be used to input messages to pagers.

The Web form of WorldCom, for example, allows users to send a text message consisting of a maximum of 240 characters to subscribers of its One-Way Alphanumeric service and 500 characters to subscribers of its Enhanced One-Way, Interactive (two-way), and QuickReply Interactive services. In addition, users can send a text message consisting of a maximum of 200 characters to subscribers of MobileComm. The form even provides a means to check the character count before the message is sent.

Telephone Network Regardless of exactly how the message is entered, it eventually passes through the PSTN to the paging terminal for encoding and transmission through the wireless paging system. Typically, the encoder accepts the incoming page, checks the validity of the pager number, looks up the directory or database for the subscriber’s pager address, and converts the address and message into the appropriate paging signaling protocol. The encoded paging signal is then sent to the transmitters (base stations), through the paging transmission control systems, and broadcast across the coverage area on the specified frequency.

Encoder Encoding devices convert pager numbers into pager codes that can be transmitted. There are two ways in which encoding devices accept pager numbers: manually and automatically. In manual encoding, a paging system operator enters pager numbers and messages via a keypad connected to the encoder. In automatic encoding, a caller dials up an automatic paging terminal and uses the phone keypads to enter pager numbers. Regardless of the method used, the encoding device then generates the paging code for the numbers entered and sends the code to the paging base station for wireless transmission.

Base Station Transmitters The base station transmitters send page codes on an assigned radio frequency. Most base stations are specifically designed for paging, but those designed for two-way voice can be used as well.

Pagers Pagers are essentially FM receivers tuned to the same radio frequency as the paging base station. Adecoder unit built into each pager recognizes the unique code assigned to the pager and rejects all other codes for selective alerting. However, pagers can be assigned the same code for group paging. There are also pagers that can be assigned multiple page codes, typically up to a maximum of four, allowing the same pager to be used for a mix of individual and group paging functions.

Despite all the enhancements built into pagers and paging services in recent years, the market is slowing down. Alphanumeric services—which provide word messages instead of just phone numbers—have failed to attract a wide audience largely because paging subscribers still need a phone to respond to messages. Some providers have tried to offer services that would allow callers to leave voice messages on pagers, but this too has failed to catch on.

Consequently, about four out of five of today’s paging customers still rely on cheap numeric services. Two-way paging networks may be the industry’s last hope for survival. They allow a pager—which comes equipped with a minikeyboard—to “talk” to another pager or with a telephone, e-mail address, or fax machine. Some two way services allow consumers to reply to messages with predetermined responses.

Signaling Protocols

In a paging system, the paging terminal, after accepting an incoming page and validating it, will encode the pager address and message into the appropriate paging signaling protocol. The signaling protocol allows individual pagers to be uniquely identified/alerted and to be provided with the additional voice message or display message, if any.

Various signaling protocols are used for the different paging service types, such as tone-only or tone and voice. Most paging networks are able to support many different paging formats over a single frequency. Many paging formats are manufacturer-specific and often proprietary, but there are public-domain protocols, such as the Post Office Code Standardization Advisory Group (POCSAG), that allow different manufacturers to produce compatible pagers.

POCSAG is a public-domain digital format adopted by many pager manufacturers around the world. It can accommodate 2 million codes (pagers), each capable of supporting up to four addresses for such paging functions as tone-only, tone and voice, and numeric display. POCSAG operates at data rates of up to 2400 bps. At this rate, to send a single tone-only page requires only 13 milliseconds. This is about 100 times faster than two-tone paging.

With the explosion of wireless technology and dramatic growth in the paging industry in many markets, existing networks are becoming more and more overcrowded. In addition, RF spectrum is not readily available because of demands by other wireless applications. In response to this problem, Motorola has developed a one-way messaging protocol called Flex (feature-rich long-life environment for executing) messaging applications that is intended to transform and broaden paging from traditional low-end numeric services into a range of PCS/PCN and other wireless applications.

Relative to POCSAG, Flex can transmit messages at up to 6400 bps and permit up to 600,000 numeric pagers on a single frequency compared to POCSAG’s 2400-bps transmission rate and 300,000 users per frequency. In addition, Flex provides enhanced bit error correction and much higher protection against the signal fades common in FM simulcast paging systems.

The combination of increased bit error correction and improved fade protection increases the probability of receiving a message intact, especially longer alphanumeric messages and data files that will be sent over PCS/PCN. Motorola also has developed ReFlex, a two-way protocol that will allow users to reply to messages, and InFlexion, a protocol that will enable high-speed voice messaging and data services at up to 112 kbps.

The hardware and software used in radio paging systems have evolved from simple operator-assisted systems to terminals that are fully computerized, with such features as message handling, scheduled delivery, user-friendly prompts to guide callers to a variety of functions, and automatic reception of messages. After tremendous growth in the last decade, from 10 million subscribers in 1990 to 60 million today, the paging industry has slowed down markedly—in large part because of cutthroat competition and increasing use of digital mobile phones.

Over-the-Air Service Activation

2010-11-09T20:53:00.001-08:00

Over-the-air service activation, sometimes called “over-theair service provisioning,” allows a potential wireless, both cellular and personal communications services (PCS), service subscriber to activate new wireless service without the intervention of a third party (e.g., authorized dealer). The use of special software enables wireless service providers to offer over-the-air service provisioning capabilities—including initial activation—plus provisioning of other innovative wireless features, such as paging and voice mail.

The process is made secure by restricting the phone’s initial use to activation only. Once subscribers have the phone in hand, they can immediately dial a customer service representative who can activate the phone and accept account information. Over-the-air activation also enables the service provider to activate a potential service subscriber’s unit by downloading over the air the required parameters, such phone number and features, into the unit.

The service subscriber does not have to bring the unit into a dealer or service agent. This allows service providers the capability to start marketing subscriber units through nontraditional mass-market retailers who do not have the personnel to individually program subscriber units. Another capability of over-the-air service activation is the ability to load an authentication key into a subscriber unit securely.

Authentication is the process by which information is exchanged between a subscriber unit and the network for the purpose of confirming and validating the identity of the subscriber unit. The over-the-air service activation feature incorporates an authentication key exchange agreement algorithm. This algorithm enhances security for the subscriber and reduces the potential for fraudulent use of cellular service.

New customers simply place a call to the cellular operator, and the information is transferred automatically to the cellular phone over the cellular airwaves. This method of activation enables cellular operators to explore new distribution channels for subscriber units and substantially reduce distribution and service provisioning costs. These features operate over a digital control channel (DCC).

In addition to over-the-air programming, the DCC supports such advanced services as calling line ID, message waiting indication, and Short Message Service (SMS). It also offers tiered services, allowing operators to tailor pricing packages for residential and business customers based on location and usage.

Sleep mode, another DCC feature, improves handset battery life by allowing mobile phones to “sleep” while idle to conserve power. DCC also improves network performance and supports advanced voice coder technology for improved audio quality.

In 1995, Code Division Multiple Access (CDMA) became the first digital cellular technology to offer instant activation to customers based on specifications defined by the CDMA Development Group (CDG) in 1994. In the future, cellular operators will look to leverage this capability to offer more value-added services, providing them with the latest applications software coming directly from the network.

Multichannel Video Distribution and Data Service

2010-11-09T20:52:00.001-08:00

Multichannel Video Distribution and Data Service (MVDDS) supports broadband communication services that include local television programming and high-speed Internet access in the 12-GHz band. This is the same band used by Direct Broadcast Satellite (DBS). The FCC adopted MVDDS service and technical rules that permit MVDDS operators to share the 12-GHz band with DBS on a coprimary basis subject to the condition that they do not cause impermissible interference to the DBS service.

Specifically, the FCC adopted equivalent power flux density (EPFD) limits for MVDDS to protect DBS subscribers from interference. MVDDS operators are required to ensure that the adopted EPFD limits are not exceeded at any existing DBS customer location. If the EPFD limits are exceeded, the MVDDS operator will be required to discontinue service until the limits can be met. MVDDS power flux density limits, MVDDS spacing rules, and coordination requirements are intended to facilitate mutual sharing of the 12-GHz band.

A“safety valve” allows individual DBS licensees or distributors to present evidence that the appropriate EPFD for a given service area should be different from the EPFD applicable in that zone. With MVDDS, the FCC adopted a geographic licensing scheme and, in the event mutually exclusive applications are filed, will assign licenses via competitive bidding.

A licensing system based on component economic areas (CEAs) will be used with one spectrum block of 500 MHz available per CEA. In setting up the rules for MVDDS, the FCC restricted dominant cable operators from acquiring an interest in an MVDDS license for a service area where significant overlap is present. There is no restriction on DBS providers from acquiring MVDDS licenses.

MVDDS providers will share the 12-GHz band with incumbent Direct Broadcast Satellite (DBS) providers on a coprimary, non-harmful interference basis. The objective of this arrangement is to accommodate the introduction of innovative services and to facilitate the sharing and efficient use of spectrum. Furthermore, the FCC believes that this service will facilitate the delivery of communications services, such as video and broadband services, to various populations, including those deemed to be unserved or underserved.

Multichannel Multipoint Distribution Service

2010-11-09T20:51:00.001-08:00

Multichannel Multipoint Distribution Service (MMDS) is a microwave technology that traces its origins to 1972 when it was introduced to provide an analog service called Multipoint Distribution Service (MDS). For many years, MMDS was used for one-way broadcast of television programming, but in early 1999, the FCC opened up this spectrum to allow for twoway transmissions, making it useful for delivering telecommunication services, including high-speed Internet access to homes and businesses.

This technology, which has now been updated to digital, operates in the 2- to 3-GHz range, enabling large amounts of data to be carried over the air from the operator’s antenna towers to small receiving dishes installed at each customer location. The useful signal range of MMDS is about 30 miles, which beats Local Multipoint Distribution Service (LMDS) at 7.5 miles and Digital Subscriber Line (DSL) at 18,000 feet. Furthermore, MMDS is easier and less costly to install than cable service.

With MMDS, a complete package of TV programs can be transmitted to homes and businesses. Since MMDS operates within the frequency range of 2 to 3 GHz, which is much lower than LMDS at 28 to 31 GHz, it can support only up to 24 stations. However, operating at a lower frequency range means that the signals are not as susceptible to interference as those using LMDS technology.

Most of the time the operator receives TV programming via a satellite downlink. Large satellite antennas installed at the head end collect these signals and feed them into encoders that compress and encrypt the programming. The encoded video and audio signals are modulated, via amplitude modulation (AM) and frequency modulation (FM), respectively, to an intermediate frequency (IF) signal.

These IF signals are up-converted to MMDS frequencies and then amplified and combined for delivery to a coaxial cable, which is connected to the transmitting antenna. The antenna can have an omnidirectional or sectional pattern. The small antennas at each subscriber location receive the signals and pass them via a cable to a set-top box connected to the television. If the service also supports highspeed Internet access, a cable also goes to a special modem connected to the subscriber’s PC.

MMDS sends data as fast as 10 Mbps downstream (toward the computer). Typically, service providers offer downstream rates of 512 kbps to 2.0 Mbps, with burst rates up to 5 Mbps whenever spare bandwidth becomes available. Originally, there was a line-of-sight limitation with MMDS technology. But this has been overcome with a complementary technology called Vector Orthogonal Frequency Division Multiplexing (VOFDM).

Because MMDS does not require an unobstructed line of sight between antennas, signals bouncing off objects en route to their destination require a mechanism for being reassembled in their proper order at the receiving site. VOFDM handles this function by leveraging multipath signals, which normally degrade transmissions.

It does this by combining multiple signals at the receiving end to enhance or recreate the transmitted signals. This increases the overall wireless system performance, link quality, and availability. It also increases service providers’ market coverage through non-line-of-sight transmission.

MMDS equipment can be categorized into two types based on the duplexing technology used: Frequency Division Duplexing (FDD) or Time Division Duplexing (TDD). Systems based on FDD are a good solution for voice and bidirectional data because forward and reverse use separate and equally large frequency bands. However, the fixed nature of this scheme limits overall efficiency when used for Internet access. This is so because Internet traffic tends to be “bursty” and asymmetric.

Instead of preassigning bandwidth with FDD, Internet traffic is best supported by a more flexible bandwidth allocation scheme. This is where TDD comes in; it is more efficient because each radio channel is divided into multiple time slots through Time Division Multiple Access (TDMA) technology, which enables multiple channels to be supported.

Because TDD has flexible timeslot allocations, it is better suited for data delivery—specifically Internet traffic. TDD enables service providers to vary uplink and downlink ratios as they add customers and services. Many more users can be supported by the allocation of bandwidth on a nonpredefined basis.

MMDS is being used to fill the gaps in market segments where cable modems and DSL cannot be deployed because of distance limitations and cost concerns. Like these technologies, MMDS provides data services and enhanced video services such as video on demand, as well as Internet access.

MMDS will be another access method to complement a carrier’s existing cable and DSL infrastructure, or it can be used alone for direct competition. With VOFDM technology, MMDS is becoming a workable option that can be deployed cost-effectively to reach urban businesses that do have lineof- sight access and in suburban and rural markets for small businesses and telecommuters.

Mobile Telephone Switching Office

2010-11-09T20:50:00.003-08:00

The Mobile Telephone Switching Office (MTSO) acts like an ordinary switching node on the Public Switched Telephone Network (PSTN) or Integrated Services Digital Network (ISDN) and provides all the functionality needed to handle a mobile subscriber, such as registration, authentication, location updating, handoffs, and call routing to a roaming subscriber. All cell phones have special codes associated with them:

Electronic Serial Number (ESN) Aunique 32-bit number programmed into the phone when it is manufactured.
Mobile Identification Number (MIN) A10-digit number derived from the mobile phone number.
System Identification Code (SID) Aunique 5-digit number that is assigned to each carrier by the FCC.

While the ESN is considered a permanent part of the phone, both the MIN and SID codes are programmed into the phone on purchase and activation with a service plan. When the mobile phone is powered up, it listens for the network operator’s SID on the control channel. The control channel is a special frequency that the phone and base station use to talk to one another about such functions as call setup and channel changing.

If the phone cannot find any control channels to listen to, it assumes that it is out of range and displays a “no service” message. When it receives the SID, the phone compares it to the SID programmed into the phone. If the SIDs match, the phone knows that the cell it is communicating with is part of its home system. Along with the SID, the phone also transmits a registration request.

The MTSO then knows the location of the phone, which is recorded in a database so that it knows which cell to target when it wants to ring that phone for an incoming call. When the MTSO gets the call, it looks up the location of the phone in its database. The MTSO picks a frequency pair the phone will use in that cell to take the call. The MTSO communicates with the phone over the control channel to tell it which frequencies to use, and once the phone and the tower switch on those frequencies, the call is connected.

As the mobile phone moves toward the edge of a cell, that cell’s base station notices that its signal strength is diminishing. Meanwhile, the base station in the cell the mobile phone is moving toward is listening and measuring signal strength on all frequencies and sees that the approaching phone’s signal strength increasing. The two base stations coordinate with each other through the MTSO, and at some point, the phone gets a signal on a control channel telling it to change frequencies.

This hand off switches the phone to the new cell. If the SID on the control channel does not match the SID programmed into the mobile phone, then the phone assumes that it is roaming. The MTSO of the cell that the phone is roaming in contacts the MTSO of its home system, which then checks its database to confirm that the SID is valid. The home system verifies the phone to the local MTSO, which then tracks it while it is moving through its cells.

The local wireless cellular network consists of a Mobile Telephone Switching Office (MTSO) with cell sites scattered throughout a geographic serving region. T-carrier or fiber lines are typically leased from the local carrier to interconnect the cell sites with the MTSO. These lines also provide the MTSO with connectivity to a local central office switch so that calls can be completed between the wireless network and the PSTN.

Microwave Communication

2010-11-09T20:50:00.001-08:00

A microwave is a short radio wave that varies from 1 millimeter to 30 centimeters in length. Because microwaves can pass through the ionosphere, which blocks or reflects longer radio waves, microwaves are well suited for satellite communications. This reliability also makes microwave well suited to terrestrial communications as well, such as those delivered by Local Multipoint Distribution Service (LMDS) and Multichannel Multipoint Distribution Service (MMDS).

Much of the microwave technology in use today for pointto- point communications was derived from radar developed during World War II. Initially, microwave systems carried multiplexed speech signals over common carrier and military communications networks; but today they are used to handle all types of information—voice, data, facsimile, and video—in either an analog or digital format.

The first microwave transmission occurred in 1933, when European engineers succeeded in communicating reliably across the English Channel—a distance of about 12 miles (20 kilometers). In 1947, the first commercial microwave network in the United States came online. Built by Bell Laboratories, this was a New York to Boston system consisting of 10 relay stations carrying television signals and multiplexed voice conversations.

A year later, New York was linked to San Francisco via 109 microwave relay stations. By the 1950s, transcontinental microwave networks were routinely handling over 2000 voice channels on hops averaging 25 miles (41.5 kilometers) in length. By the 1970s, just about every single telephone call, television show, telegram, or data message that crossed the country spent some time on a microwave link.

Over the years, microwave systems have matured to the point that they have become major components of the nation’s Public Switched Telephone Network (PSTN) and an essential technology with which private organizations can satisfy internal communications requirements. Microwave systems can even exceed the 99.99 percent reliability standard set by the telephone companies for their phone lines.

Early technology limited the operations of microwave systems to radio spectrum in the 1-GHz range, but because of improvements in solid-state technology, today’s government systems are transmitting in the 153-GHz region, while commercial systems are transmitting in the 40-GHz region with FCC approval.

The 64- to 71-GHz band is reserved for intersatellite links. These frequency bands offer short-range wireless radio systems the means to provide communications capacities approaching those now achievable only with coaxial cable and optical fiber. These spectrum allocations offer a variety of possibilities, such as use in short-range, high-capacity wireless systems that support educational and medical applications, and wireless access to libraries or other information databases.

In addition to telecommunication service providers, shorthaul microwave equipment is used routinely by hotel chains, CATV operators, and government agencies. Corporations are making greater use of short-haul microwave, especially for extending the reach of local area networks (LANs) in places where the cost of local T1 lines is prohibitive. Common carriers use microwave systems for backup in the event of fiber cuts and in terrain where laying fiber is not economically feasible.

Cellular service providers use microwave to interconnect cell sites with each other as well as to the regular telephone net-work. Some interexchange carriers (and corporations) even use short-haul microwave to bypass Incumbent Local Exchange Carriers (ILECs) to avoid lengthy service provisioning delays and to avoid paying hefty local access charges.

There are more than 25,000 microwave networks in the United States alone. There are basically two microwave network configurations: point-to-point and point-to-multipoint. The first type meets a variety of low- and medium-density communications requirements, ranging from simple links to more complex extended networks, such as:

Sub-T1/E1 data links
Ethernet/Token Ring LAN extensions
Low-density digital backbone for wide area mobile radio and paging services
PBX/OPX/FX voice, fax, and data extensions
Facility-to-facility bulk data transfer

Point-to-multipoint microwave systems provide communications between a central command and control site and remote data units. Atypical radio communications system provides connections between the master control point and remote data collection and control sites. Repeater configurations are also possible. The basic equipment requirements for a point-to-multipoint system include:

Antennas For the master, an omnidirectional antenna; for the remotes, a highly directional antenna aimed at the master station’s location.
Tower (or other structure, such as a mast) To support the antenna and transmission line.
Transmission line Low-loss coaxial cable connecting the antenna and the radio.
Master station radio Interfaces with the central computer; it transmits and receives data from the remote radio sites and can request diagnostic information from the remote transceivers. The master radio also can serve as a repeater.
Remote radio transceiver Interfaces to the remote data unit; receives and transmits to the master radio.
Management station A computer that can be connected to the master station’s diagnostic system either directly or remotely for control and collection of diagnostic information from master and remote radios.

Traditionally, cable system operators have used microwave transmission systems to link cable networks. These Cable Antenna Relay Services (CARS) have experienced declining usage as cable operators have deployed more optical fiber in their transmission systems. However, improvements in microwave technology and the opening of new frequencies for commercial use have contributed to the resurgence in shorthaul microwave.

In the broadcast industry, short-haul microwave is often referred to as “wireless cable,” which comes in the form of Local Multipoint Distribution Service (LMDS) and Multichannel Multipoint Distribution Service (MMDS). These wireless cable technologies have two key advantages.

One is availability—with an FCC license, they can be made available in areas of scattered population and other areas where it is too expensive to build a traditional cable station. The other is affordability—because of the lower costs of building a wireless cable station, savings can be passed on to subscribers.

The radio spectrum is the part of the natural spectrum of electromagnetic radiation lying between the frequency limits of 9 kHz and 400 GHz. In the United States, regulatory responsibly for the radio spectrum is divided between the FCC and the National Telecommunications and Information Administration (NTIA).

The FCC, which is an independent regulatory agency, administers spectrum for non-federal government use, and the NTIA, which is an operating unit of the Department of Commerce, administers spectrum for federal government use. Within the FCC, the Office of Engineering and Technology (OET) provides advice on technical and policy issues pertaining to spectrum allocation and use. This office manages the spectrum and provides leadership to create new opportunities for competitive technologies and services for the American public.

Microwave is now almost exclusively a short-haul transmission medium, while optical fiber and satellite have become the long-haul transmission media of choice. Short-haul microwave is now one of the most agile and adaptable transmission media available, with the capability of supporting data, voice, and video. It is also used to back up fiberoptic facilities and to provide communications services in locations where it is not economically feasible to install fiber.

Maritime Mobile Service

2010-11-09T20:48:00.001-08:00

The Maritime, or Marine, Radio Services have evolved from the earliest practical uses of radio. In 1900, just 6 years after Marconi demonstrated his “wireless” radio, devices were being installed aboard ships to enable them to receive storm warnings transmitted from stations on shore. Today, the same principle applies in using both shipboard and land stations in the marine services to safeguard life and property at sea.

Both types of stations are also used to aid marine navigation, commerce, and personal business, but such uses are secondary to safety, which has international priority. The Marine Radio Services include the Maritime Mobile Service, the Maritime Mobile-Satellite Service, the Port Operations Service, the Ship Movement Service, the Maritime Fixed Service, and the Maritime Radio determination Service.

Maritime Mobile Service is an internationally allocated radio service providing for safety of life and property at sea and on inland waterways.
Maritime Mobile-Satellite Service provides frequencies for public correspondence between ships and public coast stations as well as between aircraft and public coast stations and coast earth stations. The transmission of public correspondence from aircraft must not cause interference to maritime communications.
Port Operations Service provides frequencies for intership communications related to port operations in coastal harbors, allowing the vessel traffic to be managed more efficiently while protecting the marine environment from vessel collisions and groundings.
Ship Movement Service provides frequencies for communications relating to the operational handling of the movement and the safety of ships and, in emergency, to the safety of persons.
Maritime Fixed Service provides frequencies for communications equipment installed on oil drilling platforms, lighthouses, and maritime colleges.
Maritime Radiodetermination Service provides frequencies for determining position, velocity, and other characteristics of vessels.

Together, shipboard and land stations in the Marine Services are meant to serve the needs of the entire maritime community. The Federal Communications Commission (FCC) regulates these services both for ships of U.S. registry that sail in international and foreign waters and for all marine activities in U.S. territory.

For this and other reasons, the rules make a distinction between compulsory users of marine radio for safety at sea and noncompulsory uses for purposes other than safety. In addition, rules concerning domestic marine communications are matched to requirements of the U.S. Coast Guard, which monitors marine distress frequencies continuously to protect life and property in U.S. waters.

Low-Power Radio Service

2010-11-09T20:47:00.003-08:00

Low-Power Radio Service (LPRS) is one of the Citizens’ Band (CB) Radio Services. It is a one-way short-distance very-highfrequency (VHF) communication service providing auditory assistance to persons with disabilities, persons who require language translation, and persons in educational settings.

It also provides health care assistance to the ill, law enforcement tracking services in cooperation with a law enforcement agency, and point-to-point network control communications for Automated Marine Telecommunications System (AMTS) coast stations. In all applications, two-way voice communications are prohibited. Alicense from the FCC is not needed to use most LPRS transmitters.

To operate an LPRS transmitter for AMTS purposes, however, the user must hold an AMTS license. Otherwise, provided the user is not a representative of a foreign government, anyone can operate an FCC type-accepted LPRS transmitter for voice, data, or tracking signals. An LPRS transmitter may be operated within the territorial limits of the 50 United States, the District of Columbia, and the Caribbean and Pacific insular areas.

It also may be operated on or over any other area of the world, except within the territorial limits of areas where radio communications are regulated by another agency of the United States or within the territorial limits of any foreign government. The transmitting antenna must not exceed 30.5 meters (100 feet) above ground level. This height limitation does not apply, however, to LPRS transmitter units located indoors or where the antenna is an integral part of the unit.

There are 260 channels available for LPRS. These channels are available on a shared basis only and are not assigned for the exclusive use of any entity. Certain channels (19, 20, 50, and 151 to 160) are reserved for law enforcement tracking purposes. Further, AMTS-related transmissions are limited to the upper portion of the band (216.750 to 217.000 MHz). Users must cooperate in the selection and use of channels in order to reduce interference and make the most effective use of the authorized facilities.

Channels must be selected in an effort to avoid interference with other LPRS transmissions. This means that if users are experiencing interference on a particular channel, they should change to another channel until a clear one is found. Finally, operation is subject to the conditions that no harmful interference is caused to the U.S. Navy’s SPASUR radar system (216.88 to 217.08 MHz) or to a Channel 13 television station.

LPRS can operate anywhere CB station operation is permitted. An LPRS station is not required to transmit a station identification announcement. The LPRS transmitting device may not interfere with TV reception or federal government radar and must accept any interference received, including interference that may cause undesired operation. On request, system equipment must be available for inspection by an authorized FCC representative.

Low-Power FM Radio Service

2010-11-09T20:47:00.001-08:00

The FCC in January 2000 created two new classes of noncommercial radio stations, referred to as “low-power frequencymodulated (LPFM) radio services.” LPFM radio services are designed to serve very localized communities or underrepresented groups within communities. The LP100 service operates in the power range of 50 to 100 watts and has a service radius of about 3.5 miles.

The LP10 service operates in the power range of 1 to 10 watts and has a service radius of about 1 to 2 miles. In conjunction with the new radio services, the FCC adopted interference protection requirements based on distance separation between stations. This is intended to preserve the integrity of existing FM radio stations and safeguard their ability to transition to digital transmission capabilities.

The FCC put into place minimum distance separations as the best practical means of preventing interference between low-power radio and full-power FM stations. It requires minimum distances between stations using the same or first adjacent channels. However, third adjacent channel and possibly second adjacent channel separations may not be necessary in view of the low power levels of LPFM radio.

Eligible LPFM licensees can be noncommercial government or private educational organizations, associations, or entities; nonprofit entities with educational purposes; or government or nonprofit entities providing local public safety or transportation services. However, LPFM licenses will be awarded throughout the FM radio band and will not be limited to the channels reserved for use by noncommercial educational radio stations.

To further its goals of diversity and creating opportunities for new voices, no existing broadcaster or other media entity can have an ownership interest or enter into any program or operating agreement with any LPFM station. In addition, to encourage locally originated programming, LPFM stations will be prohibited from operating as translators.

To foster local ownership and diversity, during the first 2 years of LPFM license eligibility, licensees will be limited to local entities certifying that they are physically headquartered, have a campus, or have 75 percent of their board members residing within 10 miles of the station they seek to operate. During this time, no entity may own more than one LPFM station in any given community.

After 2 years from the date the first applications are accepted, in order to bring into use whatever low-power stations remain available but unapplied for, applications will be accepted from nonlocal entities. For the first 2 years, no entity will be permitted to operate more than one LPFM station nationwide. After the second year, eligible entities will be able to own up to five stations nationwide, and after 2 more years, up to 10 nationwide.

LPFM stations are licensed for 8-year renewable terms. These licenses are not transferable. Licensees receive fourletter call signs with the letters LP appended. In the event multiple applications are received for the same LPFM license, the FCC will implement a selection process that awards applicants one point each for:

Certifying an established community presence of at least 2 years prior to the application.
Pledging to operate at least 12 hours daily.
Pledging to air at least 8 hours of locally originated programming daily.

If applicants have the same number of points, time-sharing proposals will be used as a tiebreaker. Where ties have not been resolved, a group of up to eight mutually exclusive applicants will be awarded successive license terms of at least 1 year for a total of 8 years. These 8-year licenses will not be renewable.

LPFM stations will be required to broadcast a minimum of 36 hours per week, the same requirement imposed on fullpower noncommercial educational licensees. They will be subject to statutory rules, such as sponsorship identification, political programming, prohibitions of airing obscene or indecent programming, and requirements to provide periodic call sign announcements. They also will be required to participate in the national Emergency Alert System.

According to the FCC, the new LPFM service will enhance community-oriented radio broadcasting. During the proceedings leading up to the new classes of radio service, broad national interest in LPFM service was demonstrated by the thousands of comments received from state and local government entities, religious groups, students, labor unions, community organizations, musicians, and others supporting the introduction of a new LPFM service. The FCC expects that the local nature of the LPFM service, coupled with the eligibility and selection criteria, will ensure that LPFM licensees will meet the needs and interests of their communities.

Local Multipoint Distribution Service

2010-11-09T20:46:00.002-08:00

Local Multipoint Distribution Service (LMDS) is a two-way millimeter microwave technology that operates in the 27- to 31-GHz range. This broadband service allows communications providers to offer a variety of high-bandwidth services to homes and businesses, including broadband Internet access.

LMDS offers greater bandwidth capabilities than a predecessor technology called “Multichannel Multipoint Distribution Service” (MMDS) but has a maximum range of only 7.5 miles from the carrier’s hub to the customer premises. This range can be extended, however, through the use of optical fiber links.

LMDS provides enormous bandwidth—enough to support 16,000 voice conversations plus 200 channels of television programming. Figure L-2 contrasts LMDS with the bandwidth available over other wireless services. Competitive Local Exchange Carriers (CLECs) can deploy LMDS to completely bypass the local loops of the Incumbent Local Exchange Carriers (ILECs), eliminating access charges and avoiding service-provisioning delays.

Since the service entails setting up equipment between the provider’s hub location and customer buildings for the microwave link, LMDS costs far less to deploy than installing new fiber. This allows CLECs to very economically bring customer traffic onto their existing metropolitan fiber networks and, from there, to a national backbone network. The strategy among many CLECs is to offer LMDS to owners of multitenant office buildings and then install cable to each tenant who subscribes to the service.

The cabling goes to an on-premises switch, which is run to the antenna on the building’s roof. That antenna is aimed at the service provider’s antenna at its hub location. The line-of-sight wireless link between the two antennas offers a broadband “pipe” for multiple voice, data, and video applications. Subscribers can use LMDS for a variety of high-bandwidth applications, including television broadcast, videoconferencing, LAN interconnection, broadband Internet access, and telemedicine.

LMDS operation requires a clear line of sight between the carrier’s hub station antenna and the antenna at each customer location. The maximum range between the two is 7.5 miles. However, LMDS is also capable of operating without having a direct line-of-sight with the receiver. This feature, highly desirable in built-up urban areas, may be achieved by bouncing signals off buildings so that they get around obstructions.

At the receiving location, the data packets arriving at different times are held in queue for resequencing before they are passed to the application. This scheme does not work well for voice, however, because the delay resulting from queuing and resequencing disrupts two-way conversation. At the carrier’s hub location there is a roof-mounted multisectored antenna.

Each sector of the antenna receives/transmits signals between itself and a specific customer location. This antenna is very small, some measuring only 12 inches in diameter. The hub antenna brings the multiplexed traffic down to an indoor switch that processes the data into 53-byte Asynchronous Transfer Mode (ATM) “cells” for transmission over the carrier’s fiber network.

These individually addressed cells are converted back to their native format before going off the carrier’s network to their proper destinations—the Internet, Public Switched Telephone Network (PSTN), or customer’s remote location. At each customer’s location, there is a rooftop antenna that sends/receives multiplexed traffic.

This traffic passes through an indoor network interface unit (NIU) that provides the gateway between the RF (radio frequency) components and the in-building equipment, such as a LAN hub, Private Branch Exchange (PBX), or videoconferencing system. The NIU includes an up/down converter that changes the frequency of the microwave signals to a lower intermediate frequency (IF) that the electronics in the office equipment can manipulate more easily (and inexpensively).

In May 1999, the FCC held the last auction for LMDS spectrum. Over 100 companies qualified for the auctions, bidding against each other for licenses in select basic trading areas (BTAs). The FCC auctioned two types of licenses in each market: An “A-block” license permits the holder to provision 1150 MHz of spectrum for distribution among its customers, while a “B-block” license permits the holder to provision 150 MHz.

Most of the A-block licenses in the largest BTAs were won by major CLECs, while the B-block licenses were taken by smaller companies, Internet service providers (ISPs), universities, and government agencies. The licenses are granted for a 10-year period, after which the FCC can take them back if the holder does not have service up and running.

Development History

Bernard Bossard is generally recognized as the inventor of LMDS. Bossard, who had worked with microwaves for the military, believed that he could make point-to-multipoint video work in the 28-GHz band. Not interested in sending high-powered, low-frequency signals over long distances, Bossard focused instead on sending low-powered, high-frequency signals over a short distance. The result was LMDS.

In 1986, he received funding and formed CellularVision with his financial backers. CellularVision then spun off the technical rights to the technology into a separate subsidiary, CT&T, that licenses it to other companies. CellularVision was awarded a pioneer’s preference license by the FCC for its role in developing LMDS. CellularVision began operating a commercial LMDS in metropolitan New York, providing video programming to subscribers in the Brighton Beach area.

In 1998, CellularVision changed its name to SPEEDUS.COM. The company has a network operations center and recently has been expanding the number of operating cells in the New York area and now claims more than 12,000 residential and business subscribers. SPEED service is delivered via 14 fully functional Internet broadcast stations in operation under SPEEDUS.COM’s FCC license covering metropolitan New York.

SPEED subscribers are able to browse the Web using the company’s SPEED modem capable of downstream speeds of up to 48 Mbps, which is 31 times faster than a full T1 line. In the SPEEDUS.COM system, cable programming is downlinked from satellites to the company’s head-end facility, where local broadcast transmissions are also received. At the company’s master control room, the programming signals are then amplified, sequenced, scrambled, and up-converted to 28 GHz.

The SPEED.COM transmitters and repeaters then broadcast a polarized FM signal in the 28-GHz band over a radius of up to 3 miles to subscribers and to adjacent cells for transmission. A6-inch-square, highly directional, flat-plate, window- , roof- , or wall-mounted antenna receives the scrambled signal and delivers it to the addressable settop converter, which decodes the signals. The subscriber receives 49 channels of high-quality video and audio programming, including pay-per-view and premium channels.

Over 100 companies own licenses for LMDS. XO Communications (formerly known as Nextlink) is one of the largest single holders of LMDS licenses in the United States, having invested over $800 million in such systems, largely through the acquisition of other companies that held LMDS licenses. XO is a CLEC and is using LMDS to feed traffic to its fiber networks. Its approach to building out a city is to install fiber. In areas where that will take too long or where permits are too hard to come by, XO will use, in this order, LMDS, Digital Subscriber Line (DSL), and ILEC facilities.

Potential Problems

A potential problem for LMDS users is that the signals can be disrupted by heavy rainfall and dense fog—even foliage can block a signal. In metropolitan areas where new construction is a fact of life, a line-of-sight transmission path can disappear virtually overnight. For these reasons, many information technology (IT) executives are leery of trusting mission-critical applications to this wireless technology.

Service providers downplay this situation by claiming that LMDS is just one local access option and that fiber links are the way to go for mission-critical applications. In fact, some LMDS providers offer fiber as a backup in case the microwave links experience interference. There is controversy in the industry about the economics of the point-to-multipoint architecture of LMDS, with some experts claiming that the business model of going after lowusage customers is fundamentally flawed and will never justify the service provider’s cost of equipment, installation, and provisioning.

With an overabundance of fiber in the ground and metropolitan area Gigabit Ethernet services coming online at a competitive price, the time for LMDS may have come and gone. In addition, newer wireless technologies like free-air laser hold a significant speed advantage over LMDS, as does submillimeter transmission in the 60- and 95-GHz bands. Another problem that has beset LMDS is that the major license holders have gotten caught up in financial problems, some declaring Chapter 11 bankruptcy.

These carriers built their networks quickly, incurring massive debt, without lining up customers fast enough. This strategy worked well as long as the capital markets were willing to continue funding these companies. But once the capital markets dried up in 2000, so did the wireless providers’ coffers and their immediate prospects. The uncertain future of these financially strapped carriers has discouraged many companies from even trying LMDS.

Fiberoptics is the primary transmission medium for broadband connectivity today. However, of the estimated 4.6 million commercial buildings in the United States, 99 percent are not served by fiber. Businesses are at a competitive disadvantage in today’s information-intensive world unless they have access to broadband access services, including highspeed Internet access.

These businesses, including many data-intensive high-technology companies, can be served adequately with LMDS. Despite the financial problems of LMDS providers, the technology has the potential to become a significant portion of the global access market, which will include a mix of many technologies, including DSL, cable modems, broadband satellite, and fiberoptic systems.

Laser Transmission

2010-11-09T20:46:00.000-08:00

Arelatively new category of wireless communication uses laser, sometimes called “free-space optics,” operating in the near-infrared region of the light spectrum. Utilizing coherent laser light, these wireless line-of-sight links are used in campus environments and urban areas where the installation of cable is impractical and the performance of leased lines is too slow.

Laser links between sites can be operated at the full local area network (LAN) channel speed. And unlike microwave transmission, laser transmission does not require a Federal Communications Commission (FCC) license, and data traveling by laser beam cannot be intercepted.

The lasers at each location are aligned with a simple bar graph and tone lock procedure. Fiberoptic repeaters are used to connect the LANs to the laser units. Alternatively, a bridge equipped with a fiberoptic to attachment unit interface (AUI) transceiver may be used. Connections to and from the laser are made using standard fiberoptic cable, protecting data from radio frequency interference (RFI) and electromagnetic interference (EMI).

Monitors can be attached to the laser units to provide operational status, such as signal strength, and to implement local and remote loop-back diagnostics. The reason that laser products are not used very often for business applications is that transmission is affected by atmospheric conditions that produce such effects as absorption, scattering, and shimmer. All three can reduce the amount of light energy that is picked up by the receiver and corrupt the data being sent.

Absorption refers to the ability of various frequencies to pass through the air. Absorption is determined largely by the water vapor and carbon dioxide content of the air along the transmission path, which, in turn, depends on humidity and altitude. The gases that form in the atmosphere have many resonance bands that allow specific frequencies of light to pass.

These transmission windows occur at various wavelengths, such as the visible light range. Another window occurs at the near-infrared wavelength of approximately 820 nanometers (nm). Laser products tuned to this window are not greatly affected by absorption. Scattering has a much greater effect on laser transmission than absorption. The atmospheric scattering of light is a function of its wavelength and the number and size of scattering particles in the air.

The optical visibility along the transmission path is directly related to the number and size of these particles. Fog and smog are the main conditions that tend to limit visibility for optical-infrared transmission, followed by snow and rain. Shimmer is caused by localized differences in the air’s index of refraction. This is caused by a combination of factors, including time of day (daytime heat), terrain, cloud cover, wind, and the height of the optical path above the source of shimmer.

These conditions cause fluctuations in the received signal level by directing some of the light out of its intended path. Beam fluctuations may degrade system performance by producing short-term signal amplitudes that approach threshold values. Signal fades below these threshold values result in error bursts.

Vendors have taken steps to mitigate the effects of absorption, scatter, and shimmer. For example, such techniques as frequency modulation (FM) in the transmitter and an automatic gain control (AGC) in the receiver can minimize the effects of shimmer. Also, selecting an optical path several meters above heat sources can greatly reduce the effects of shimmer.

However, all of these distorting conditions can vary greatly within a short time span or persist for long periods, requiring onsite expertise to constantly fine-tune the system. Many businesses simply cannot risk frequent or extended periods of downtime while the necessary compensating adjustments are being made. As if all this were not enough, there are other potential problems to contend with, such as thermal window coatings and the laser beam’s angle of incidence, both of which can disrupt transmission.

These problems are being overcome with newer lasers that operate in the 1550-nanometer (nm) wavelength. A1550-nanometer delivery system is powerful enough to go through windows, can deliver signals under the fog blanket, and is safe enough that it does not blind the casual viewer who happens to look into the beam. Up to 1 Gbps of bandwidth is available with these systems—the equivalent bandwidth capacity of 660 T1 lines.

There is also a distance limitation associated with laser. The link generally cannot exceed 1.5 kilometers (km), and 1 kilometer is preferred. With 1550-nanometer systems, the practical distance of the link is only 500 meters.

Despite its limitations, laser, or free-space optics, can provide a valuable last link between the fiber network and the end user—including as a backup to more conventional methods, such as fiber. Free-space optics, unlike other transmission technologies, are not tied to standards or standards development. Vendors simply attach their equipment into existing fiber-based networks and then use any laser transmission methods they like. This encourages innovation, differentiation, and speed of deployment.