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2.3] What is CSMA/CD?




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This article is from the Ethernet FAQ, by James Messer James@NetworkUptime.com with numerous contributions by others.

2.3] What is CSMA/CD?

Carrier Sense Multiple Access with Collision Detection is the basis
for the Ethernet standard, and this provides specific rules for
allowing stations to communicate over the same transmission medium.
There are a number of steps involved in communicating with CSMA/CD.

Stations must listen for a carrier on the wire. If no carrier is
detected, stations can begin transmitting. While transmitting, the
station continues to listen on the wire to ensure successful
communications. If two stations attempt to transmit information at
the same time, the transmissions overlap and cause a collision.

If a collision occurs, the transmitting station recognizes the
interference on the network and transmits a bit sequence called
jam. The jam helps to ensure that the other transmitting station
recognizes that a collision has occurred. After a random delay, the
stations attempt to retransmit the information and the process
begins again.

 

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