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

7.6. Full Duplex Application Environments

Half duplex LANs have been in use for decades in every conceivable LAN application environment. No special conditions are required in order to use traditional half duplex LANs. They can operate on dedicated or nondedicated media (for example, twisted pair or coaxial cable), provide dedicated or nondedicated bandwidth (switched or shared LAN), and are usable with any type of device with equal ease. Full duplex LANs are usable only in specific configurations that have both dedicated media capable of supporting simultaneous bidirectional communications, and exactly two devices on the LAN (microsegmentation).

While the use of dedicated media and switched LAN configurations meeting these requirements is rapidly increasing, there is still a huge installed base of legacy LANs that cannot currently support full duplex operation. In addition, switches are more expensive than shared LAN hubs, and may not be justified for general-purpose use. Thus, full duplex operation is most often seen in:

• Switch-to-switch connections

• Server and router connections

• Long-distance connections

7.6.1. Switch-to-Switch Connections

It makes sense to use full duplex mode where possible on connections between switches in a switched infrastructure. Switch-to-switch connections:

• Can take advantage of the increased capacity because of the generally symmetrical traffic distribution in a backbone environment.

• Meet the two-station LAN requirement of full duplex-mode operation. ...