Chapter 2. The Ethernet System

An Ethernet Local Area Network (LAN) is made up of hardware and software working together to deliver digital data between computers. To accomplish this task, four basic elements are combined to make an Ethernet system. This chapter provides a tutorial describing these elements, since a familiarity with these basic elements provides a good background for working with Ethernet. We will also take a look at some network media and simple topologies. Finally, we will see how the Ethernet system is used by high-level network protocols to send data between computers.

This chapter describes the original half-duplex mode of operation. Half-duplex simply means that only one computer can send data over the Ethernet channel at any given time. In half-duplex mode, multiple computers share a single Ethernet channel by using the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) media access control (MAC) protocol. Until the introduction of switching hubs, the half-duplex system was the typical mode of operation for the vast majority of Ethernet LANs—tens of millions of Ethernet connections have been installed based on this system.

However, these days many computers are connected directly to their own port on an Ethernet switching hub and do not share the Ethernet channel with other systems. This type of connection is described in Chapter 18. Many computers and switching hub connections now use full-duplex mode, in which the CSMA/CD protocol is shut off ...

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