The main hardware in a WLAN client adapter is a half-duplex radio transceiver, which can exist in many different hardware formats and chipsets. All client adapters require a special driver to interface with the operating system and software utilities to interface with the end user.

Many cards can work with Windows, Linux, and Macintosh, requiring a different driver and client software for each operating system. The drivers for many manufacturers’ cards may already be included in the operating system, but often newer cards require or can benefit from an updated driver installation.

Most vendors will provide a CD disk with an automated driver installation wizard; however, some may require that the driver be installed manually in the operating system.

With a software interface, the end user can configure a card to participate in a WLAN using configuration settings that pertain to identification, security, and performance.

These client utilities may be the manufacturer’s own software utility or an internal software interface built into the operating system. In the following, we will discuss the various radio card formats, the chipsets that are used, and software client utilities.

Radio Card Formats

Radio cards are used in both client adapters and access points. For many years, the only option you had when purchasing an 802.11 client adapter was a standard PCMCIA type adapter. A PCMCIA adapter is also known as a PC Card and is pictured in Figure below.

The PCMCIA radio card can be used in any laptop or handheld device that has a PC Card slot. Most PCMCIA cards have integrated antennas. Some cards only have internal integrated antennas, while other have both integrated antennas and external connectors.

The radio format that is becoming the most widely used is the Mini PCI . The Mini PCI is a variation of the Peripheral Component Interconnect (PCI) bus technology and was designed for use mainly in laptops.

A Mini PCI radio is often used inside access points and is also the main type of radio used by manufacturers as the internal 802.11 wireless adapter inside laptops.

It is almost impossible to buy a brand-new laptop today that does not have an internal 802.11 Mini PCI radio card, pictured in Figure below.

The Mini PCI card typically is installed from the bottom of the laptop and is connected to small diversity antennas that are mounted along the edges of the laptop’s monitor.

Secure Digital (SD) and Compact Flash (CF) are two radio card formats that are often used with handheld PDAs. These cards typically require very low power and are smaller than the size of a matchbook.

Compact Flash radio cards can sometimes be used in the PC slot of a laptop with the aid of a CF-to-PCMCIA adapter. So far we have discussed client adapters that are used with laptops or handheld devices.

802.11 client adapters also exist for desktops in the form of 802.11 PCI adapters or USB client adapters. Many 802.11 PCI adapters are simply a PCI peripheral card with a PCMIA card attached or soldered onto the PCI card.

Most desktop users place their computers underneath a desk. Therefore, the integrated antenna of an 802.11 PCI adapter is surrounded by the desk, resulting in poor communications.

Newer 802.11 PCI adapters have an integrated radio card with a jack for an external antenna so that the user may place the antenna on the top of the desk for better transmission and reception. Both examples of 802.11 PCI adapters are shown in Figure below.

The USB 802.11 radio adapter is a very popular choice because almost all computers have USB ports. USB technology provides simplicity of setup as well as no need for an external power source.

802.11 USB radio adapters exist either in the form of a small dongle device (see Figure below) or as an external wired USB device with a separate USB cable connector.

The dongle devices are compact and portable for use with a laptop computer, while with the external devices can be connected to a desktop computer with a USB extension cable and placed on top of a desk for better reception.

We have discussed the various types of 802.11 radio card formats that are used with laptops, PDAs, and desktops. 802.11 radio cards are also used in many other types of handheld devices, such as the bar code scanner and Wi-Fi VoIP phones pictured in Figure below.

It should be noted that 802.11 radio cards used as client devices have begun to show up in all sorts of machines and solutions. Radio cards already exist in gaming devices, stereo systems, and video cameras.

Appliance manufacturers are experimenting with putting Wi-Fi cards in washing machines and refrigerators. Because of the low cost of 802.11 radio cards, in the not-too-distant future your entire house might be networked wirelessly and able to be controlled from remote locations.

Another future technology also being talked about lately is the software defined radio (SDR). SDRs will be able to dynamically switch across a wide range of frequency bands, transmission techniques, and modulation schemes so that a single radio could replace multiple hardware designs.

At the time of this writing, one vendor has already received permission from the FCC to use SDR 802.11a radios to transmit in new unlicensed bands in the 5 GHz frequency range. Software defined radios may even have the capability to switch between different wireless technologies such as Wi-Fi and WiMAX.

Radio Card Chipsets

A group of integrated circuits designed to work together is often marketed as a chipset. Many 802.11 chipset manufacturers exist and sell their chipset technology to the various radio card manufacturers.

Legacy chipsets will obviously not support all of the same features as newer chipset technologies. For example, a legacy chipset may support only DSSS while newer chipsets will support both DSSS and ERP-OFDM.

Some chipsets may only support the ability to transmit on the 2.4 GHz ISM band, while other chipsets can transmit on either the 2.4 GHz or 5 GHz unlicensed frequencies and are used in 802.11a/b/g client cards.

The chipset manufacturers incorporate newer 802.11 technologies as they develop. Many proprietary technologies turn up in the individual chipsets, and some of these technologies become part of the standard in future 802.11amendments.

Client Utilities

An end user must have the ability to configure a wireless client card. Therefore, a software interface is needed in the form of client utilities. The software interface will usually have the ability to create multiple connection profiles.

One profile may be used to connect to the wireless network at work, another for connecting at home, and a third for connecting at a hotspot.

Configuration settings for a client utility typically include the service set identifier (SSID), transmit power, security settings, 802.11e/QoS capabilities, and power management settings. Any client card can also be configured for either Infrastructure or Ad-Hoc mode.

Most good client utilities will typically have some sort of statistical information display along with some sort of received signal strength measurement indicator tool. Four major types or categories of client utilities exist:

• Small office, home office (SOHO) client utilities
• Enterprise-class client utilities
• Integrated operating system client utilities
• Third-party client utilities

SOHO client utilities are usually very simplistic in nature and are designed for ease of use for the average home user. Surprisingly, though, many of the SOHO utilities support some rather advanced features as 802.11 technologies progress.

Enterprise-class client utilities provide the software interface for the more expensive enterprise-grade vendor cards. Typically, the enterprise-class utilities support more configuration features and have better statistical tools.

The most widely used client utility is an integrated operating system client utility, more specifically known as the Wireless Zero Configuration (WZC) service, that is enabled by default in Windows XP. The WZC is pictured in Figure below.

The main advantage of the WZC is that as an administrator, you only have to support one client utility even though your end users may have different radio cards.

It should be noted that the WZC has many published security risks, and therefore many government agencies and corporations ban the use of the integrated operating system utilities.

Other disadvantages of the WZC is that it supports only a limited number of EAP-type protocols and does not have a built -in received signal measurement tool.

An added advantage of the WZC is that it utilizes a proprietary roaming method called opportunistic PMK caching that is supported by many of the wireless switching vendors.

The last type of software interface for an 802.11 radio card is a third-party client utility, such as Juniper Networks Odyssey Access Client pictured in Figure below.

Much like the WZC, a third-party utility will work with radio cards from different vendors, making administrative support much easier.

Third-party client utilities often bring the advantage of supporting many different EAP types, giving a WLAN administrator a wider range of security choices. The main disadvantage of third-party client utilities is that they cost extra money.