Half- and Full-Duplex

Half-duplex works optimally only if one device is transmitting and all the other devices are receiving, otherwise, collisions occur. When the collisions are detected, the devices causing the collision wait for a random time before retransmitting.

This means that at half duplex, Ethernet throughput is limited by the need to retransmit data when collisions occur. Half-duplex is the most common transmission method and is adequate for normal workstation and PC connections.

Full duplex provides dual communication on a point-to-point connection and allows each device to simultaneously transmit and receive on a connection. Full-duplex mode is typically used to connect to other switches or to connect fast access devices, such as workgroup servers.

wpeB.jpg (14283 bytes)

Note:

To use full-duplex communication, both ends of the connection must be configured to operate in full-duplex mode, and the connecting device must have a full-duplex adapter installed. Full-duplex operation is possible only on point-to-point Ethernet connections that use separate conductors or fibers for transmit and receive, such as 10Base-T and 100Base-FX cabling. Full-duplex operation is not possible on connections using coaxial or AUI (10Base-5) cables or with most hubs.

When to use full-duplex

Some servers perform better using full duplex because they simultaneously handle traffic from many clients, some are transmitting data to the server, while others are receiving data from the server. Switch-to-switch connections certainly benefit from full-duplex transmission.

Individual workstations normally run applications traditionally written for half-duplex, request/response network connections, and are unlikely to benefit from being configured as full duplex. For example, the application may request a service on a server and then wait for a reply before continuing operations. In this case, if the server connection was full duplex, the server might respond to the request while simultaneously receiving from another station; a full-duplex connection for the workstation would typically offer no advantage.

Auto duplex

Auto duplex negotiates whether the attached device is transmitting in half or full duplex, and then automatically changes that port to that mode.


Procedures

*Legal Information © 2000 Intel Corporation