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C H A P T E R 2
Chapter Goals
• Learn about different LAN protocols.
• Understand the different methods used to deal with media contention.
• Learn about different LAN topologies.
Introduction to LAN Protocols
This chapter introduces the various media-access methods, transmission methods, topologies, and
devices used in a local-area network (LAN). Topics addressed focus on the methods and devices used in
Ethernet/IEEE 802.3, Token Ring/IEEE 802.5, and Fiber Distributed Data Interface (FDDI). Subsequent
chapters in Part II, “LAN Protocols,” address specific protocols in more detail. Figure 2-1 illustrates the
basic layout of these three implementations.
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Chapter 2
Introduction to LAN Protocols
What Is a LAN?
Figure 2-1
Three LAN Implementations Are Used Most Commonly
What Is a LAN?
A LAN is a high-speed data network that covers a relatively small geographic area. It typically connects
workstations, personal computers, printers, servers, and other devices. LANs offer computer users many
advantages, including shared access to devices and applications, file exchange between connected users,
and communication between users via electronic mail and other applications.
LAN Protocols and the OSI Reference Model
LAN protocols function at the lowest two layers of the OSI reference model, as discussed in Chapter 1,
“Internetworking Basics,” between the physical layer and the data link layer. Figure 2-2 illustrates how
several popular LAN protocols map to the OSI reference model.
FDDI
Token Ring/IEEE 802.5
Ethernet/IEEE 802.3
100BaseT
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Chapter 2
Introduction to LAN Protocols
LAN Media-Access Methods
Figure 2-2
Popular LAN Protocols Mapped to the OSI Reference Model
LAN Media-Access Methods
Media contention occurs when two or more network devices have data to send at the same time. Because
multiple devices cannot talk on the network simultaneously, some type of method must be used to allow
one device acce