The All-New Switch Book: The Complete Guide to LAN Switching Technology, Second Edition

Chapter 7. Full Duplex Operation

The popular LAN technologies all provide two important characteristics:

• Full connectivity: Stations on a LAN see themselves as directly connected to all other stations on the same LAN.

• High speed: Communication between stations is fast. The communications channel provides more capacity than any single station requires in the steady state.

Traditionally, LANs provided a means for multiple devices to share a common high-speed communications channel. The key word was share; in addition to providing connectivity, LAN technology offered a way to take an expensive resource (the high-speed channel) and spread its cost and capacity among multiple stations. As such, stations were expected to be able to use the channel only intermittently, when it was not being used by other stations. With a shared common channel, it was generally not possible to both transmit and receive at the same time; traditional LANs all operated in half duplex mode, with one station transmitting at any given time.

The use of dedicated media connections and low-cost switches changes the channel architecture in such a way that it becomes possible for a station to transmit and receive simultaneously. In this chapter, we look at the concept of full duplex LAN operation.