Packet Guide to Core Network Protocols

Chapter 2. Ethernet

Computers cabled together in a network are almost certainly going to be connected via Ethernet. Ethernet is a technology that describes the rules used for communication between LAN-based systems and is considered a Layer-2 protocol. This chapter discusses the structure and operation of the Ethernet protocol, the differences between Ethernet Type II and 802.3, cabling types, and deployment considerations.

A historical review of the current standards can be a little confusing. The story begins in the 1970s with Bob Metcalfe, who envisioned a cable-based network, which later evolved into Ethernet Type II. Shortly after Metcalfe’s ideas were disseminated, the IEEE standards committee developed 802.3 Ethernet. Both versions are in use today and are described more fully below. For the information-hungry, some interesting documents to read include:

• “Ethernet: Distributed Packet Switching for Local Computer Networks” (Metcalfe and Boggs)

• “The Ethernet: A Local Area Network Physical Layer and Data Link Layer Protocol Specifications” (DEC, Intel, and Xerox)

• “802.3-1985 IEEE Standard for Local and Metropolitan Area Networks: Carrier Sense Multiple Access with Collision Detection (Original 10Mb/s Standard)” (IEEE Standards Association)

The first paper, written by Bob Metcalfe and David Boggs, describes Ethernet as a LAN system with such characteristics as shared communication, broadcast packet switching (all nodes hear the transmission), extension via repeaters, distributed control ...