Foundation Topics

Ethernet is the undisputed king of LAN standards today. Fifteen years ago, people wondered whether Ethernet or Token Ring would become win the battle of the LANs. Eight years ago, it looked like Ethernet would win that battle, but it might lose to an upstart called Asynchronous Transfer Mode (ATM) in the LAN. Today when you think of LANs, no one even questions what type—it's Ethernet.

Ethernet has remained a viable LAN option for many years because it has adapted to the changing needs of the marketplace while retaining some of the key features of the original protocols. From the original commercial specifications that transferred data 10 megabits per second (Mbps) to the 10 gigabits per second (Gbps) rates today, Ethernet has evolved and become the most prolific LAN protocol ever.

Ethernet defines both Layer 1 and Layer 2 functions, so this chapter starts with some basic concepts in relation to OSI Layers 1 and 2. After that, the three earliest Ethernet standards are covered, focusing on the physical layer details. Next, this chapter covers data link layer functions, which are common among all the earlier Ethernet standards as well as the newer standards. Finally, two of the more recent standards, Fast Ethernet and Gigabit Ethernet, are introduced.

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