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To access the contents, click the chapter and section titles.
Wireless Networking Handbook
The IEEE 802.3, 802.5, and 802.11 specifications are part of the overall IEEE standards hierarchy (see fig. 8.5). IEEE defines a LAN with three layers of functionality: Logical Link Control (LLC), Medium Access Control (MAC), and physical layers. The LLC, which is IEEE 802.2, provides link synchronization, and the MAC layer is responsible for medium access. The physical layer defines electrical characteristics of the signal and medium. Thus, 802.3, 802.5, and 802.11 not only specify the medium access method but also the type of medium. The LAN Backbone section in this chapter provides more details on possible physical layers offered by 802.3 and 802.5.
IEEE 802.3 Carrier Sense Multiple AccessThe IEEE 802.3, released in 1980, is the most popular access method. It operates at 10 or 100 Mbps, depending on the type of physical layer used. The use of this standard satisfies most performance requirements, and, because of its high degree of proliferation, products are low cost compared to token ring and FDDI. Therefore, consider IEEE 802.3 as your wired network medium access standard, unless you require real-time data transfers or a high bandwidth. For those needs, you may want to consider IEEE 802.5 or FDDI. IEEE 802.3 is based on the ethernet protocol developed by Xerox Corporations Palo Alto Research Center (PARC) in the 1970s. Shortly after the release of the 802.3 standard, Digital Equipment Corporation, Intel Corporation, and Xerox Corporation jointly developed and released a very similar ethernet specification (Version 2.0). Today, most organizations use the IEEE 802.3 specification, which is commonly called ethernet, as a basis for their LANs. As shown in figure 8.6, IEEE 802.3 and the ethernet specification describe a slightly different frame header; therefore, these protocols are not compatible.
The following describe each of the 802.3 and ethernet frame header fields:
IEEE 802.5 Token RingThe IEEE 802.5 standard specifies a 4 and 16 Mbps token ring LAN. Stations connected to the LAN take turns sending information to other stations by utilizing a token as explained in Chapter 2 within the section Point-To-Point Infrared LAN System. Because of the token access method, 802.5 supports heavier traffic under more stable conditions than 802.3 ethernet. In addition, 802.5 supports deterministic access to the medium, which enables it to handle synchronous type information transfers. IEEE 802.5 is the second most popular LAN medium access technique and is more expensive to implement than ethernet. But, as mentioned earlier, use token ring in cases where you need better performance. The first token-ring network was developed by IBM in the 1970s; then IEEE wrote the IEEE 802.5 specification based on IBMs work. Today, IBM Token Ring and IEEE 802.5 networks are compatible, although there are minor differences. For instance, IBMs Token Ring network specifies a star configuration with all end stations attached to a device called a multistation access unit (MSAU). IEEE 802.5 does not specify a topology, but most 802.5 implementations are also based on a star configuration. Also, IEEE 802.5 does not specify a media type, but IBM Token Ring identifies the use of twisted-pair wire. The following section explains the purpose of each field. Tokens
Data/Command Frames
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