A computer network is a system that provides communications between computers. Computer networks can be configured as peer to peer, as client/server, or as centralized Central Processing Units (CPUs) with distributed dumb terminals.
A networking topology is defined simply as the physical and/or logical layout of nodes in a computer network. Any individual who has taken a networking basics class is already familiar with bus, ring, star, mesh, and hybrid topologies that are often used in wired networks.
All topologies have advantages and disadvantages. A topology may cover very small areas or can exist as a worldwide architecture. Wireless topologies also exist as defined by the physical and logical layout of wireless hardware.
Many wireless technologies exist and can be arranged into four major wireless networking topologies. The 802.11 standard defines one specific type of wireless communications.
Within the 802.11 standard exists three types of topologies, known as service sets. Over the years, vendors have also made use of 802.11 hardware using nonstandard topologies to meet specific wireless networking needs.
Wireless Networking Topologies
While the main focus of this study guide is 802.11 wireless networking, which is a local area technology, other wireless technologies and standards exist in which wireless communications span either smaller or larger areas of coverage.
Examples of other wireless technologies are cellular telephone, Bluetooth, and ZigBee. All of these different wireless technologies may or may not be arranged into four major wireless topologies:
- Wireless Wide Area Network (WWAN)
- Wireless Metropolitan Area Network (WMAN)
- Wireless Personal Area Network (WPAN)
- Wireless Local Area Network (WLAN)
Additionally, although the 802.11 standard is a WLAN standard, the same technology can sometimes be deployed in different wireless network architectures.
Wireless Wide Area Network (WWAN)
A wide area network (WAN) covers a vast geographical area. A WAN might traverse an entire state, region, or country or even span worldwide. The best example of a WAN is the Internet. Many private and public corporate WANs consist of hardware infrastructure such T1 lines, fiber optics, and routers.
Protocols used for wired WAN communications include Frame Relay, ATM, MPLS, and others. A wireless wide area network (WWAN) also covers broad geographical boundaries but obviously uses a wireless medium instead of a wired medium. Wireless wide area networks typically use cellular telephone technologies.
Cellular providers such as T-Mobile, Verizon, and Vodaphone use a variety of competing technologies to carry data. Some examples of these cellular technologies are GPRS, CDMA, TDMA, and GSM. Data can be carried to a variety of devices such as cell phones, PDAs, and cellular networking cards, as pictured in Figure 1.
Data rates and bandwidth using these technologies are relatively slow when compared to other wireless technologies, such as 802.11. However, as cellular technologies improve, so will cellular data transfer rates. It is important to understand that 802.11 wireless networking infrastructure cannot be deployed as a WWAN.
Wireless Metropolitan Area Network (WMAN)
A wireless metropolitan area network (WMAN) provides coverage to a metropolitan area such as a city and the surrounding suburbs. WMANs have been created for some time by matching different wireless technologies, and recent advancements have made this more practical.
The wireless technology that is newly associated with a WMAN is defined by the 802.16 standard. The 802.16 standard defines broadband wireless access and is sometimes referred to as Worldwide Interoperability for Microwave Access (WiMAX).
The WiMAX Forum is responsible for compatibility and interoperability testing of wireless broadband equipment such as 802.16 hardware. 802.16 technologies are viewed as a direct competition to other broadband services such as DSL and cable.
Although 802.16 wireless networking is normally thought of as a last mile data delivery solution, the technology might also be used to provide access to users over citywide areas.
Currently most 802.16 and WiMAX deployments are still in the testing phase; however, widespread practical wireless broadband deployments are possible in the foreseeable future.
A lot of press has recently been generated about the possibility of citywide deployments of Wi-Fi networks, giving city residents access to the Internet throughout a metropolitan area.
Although 802.11 technology was never intended to be used to provide access over such a wide area, at the time this book was written, cities such as Philadelphia and San Francisco had initiatives to achieve this very feat.
The equipment being used for these large-scale 802.11 deployments is proprietary wireless mesh routers or mesh access points. It remains to be seen if 802.11 wireless networking can be scaled successfully in WMAN topology.
Currently some 802.11 WMAN deployments do exist; however, they have not been running long enough to determine scalability.
Wireless Personal Area Network (WPAN)
A wireless personal area network (WPAN) is a wireless computer network used for communication between computer devices within close proximity of a user. Devices such as laptops, personal digital assistants (PDAs), and telephones can communicate with each other using a variety of wireless technologies.
WPANs can be used for communication between devices or as portals to higher-level networks such as a local area networks (LANs) and/or the Internet. The most common technologies in wireless personal area networks are Bluetooth and infrared.
Infrared is a light-based medium, while Bluetooth is a radio frequency medium that uses frequency hopping spread spectrum (FHSS) technology. Figure 2 pictures a headset and a cellular telephone that use Bluetooth radios to provide wireless connectivity between the two devices.
The IEEE 802.15 Working Group focuses on technologies used for WPANs such as Bluetooth and ZigBee. ZigBee is another RF medium that has the potential of low-cost wireless networking between devices in a WPAN architecture.
The best example of 802.11 radios being used in a wireless personal area networking scenario would be as peer-to-peer connections.