802.3/Ethernet

Reference:
http://www.dcs.gla.ac.uk/~lewis/networkpages/m04s03EthernetFrame.htm

To send a frame, a station on an 802.3 network first listens to the Ether (carrier sense function). If the Ether is busy, the station defers, but, after the current activity stops, it uses a 1-persistent strategy and will wait only for a short, fixed delay, the inter-frame gap, before beginning to transmit. If there is no collision, the transmission will complete successfully. If, however, a collision is detected, the frame transmission stops and the station begins to send a jamming signal�to make sure that all other stations realise what has happened. The station then backs off for a random time interval before trying again. The back-off�interval is computed using an algorithm called truncated binary exponential backoff, which works as follows.

The station always waits for some multiple of a 51.2ms time interval, known as a slot. The station chooses a number randomly from the set {0,1} and waits for that number of slots. If there is another collision it waits again, but this time for a number chosen from {0,1,2,3}. After k collisions on the same transmission it chooses its number randomly from {0, �, 2k-1}, until k = 10, when the set is frozen. After k = 16, the so-called attempt limit, the MAC unit gives up and reports a failure to the layer above.