IEEE 802.3

IEEE 802.3

The IEEE 802.3 standard defines a network derived from the Ethernet network originally developed by Digital, Intel, and Xerox. This standard defines characteristics related to the MAC sublayer of the Data Link layer and the OSI Physical layer. With one minor distinction—frame type—IEEE 802.3 Ethernet functions identi-cally to DIX Ethernet v.2. These two standards can even coexist on the same cabling system, although devices using one standard cannot communicate directly with devices using the other.

The MAC sublayer uses a type of contention access called Carrier Sense Multiple Access with Collision Detection (CSMA/CD). This technique reduces the incidence of collision by having each device listen to the network to determine whether it’s quiet (“carrier sensing”); a device attempts to transmit only when the network is quiescent. This reduces but does not eliminate collisions because signals take some time to propagate through the network. As devices transmit, they continue to listen so they can detect a collision should it occur. When a collision occurs, all devices cease transmitting and send a “jamming” signal that notifies all stations of the collision. Then, each device waits a random amount of time before attempting to transmit again. This combination of safeguards significantly reduces collisions on all but the busiest networks.