Truncated binary exponential backoff: Difference between revisions

Revision as of 14:01, 18 January 2006

Revision as of 17:44, 18 January 2006

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Examples are the retransmission of [[packets]] in [[carrier sense multiple access with collision avoidance]] (CSMA/CA) and [[carrier sense multiple access with collision detection]] (CSMA/CD) networks, where this algorithm is part of the channel access method used to send data on these network. In [[Ethernet]] networks, the algorithm used to schedule retransmission after a collision is that the retransmission is delayed by an amount of [[time]] derived from the [[slot time]] and the number of attempts to retransmit.

After i collisions, a random number of slot times between 0 and <math>2^i-1</math> is chosen. So, for the first collision, each sender might wait 0 or 1 slot times. After the second collision, the senders might wait 0, 1, 2, or 3 slot times, and so forth. As the number of retransmitionretransmission attempts increases, the number of possibilities for delay increases.

The 'truncated' simply means that after a certain number of increases, the exponentiation stops; i.e. the retransmission timeout reaches a ceiling, and thereafter does not increase any further. The ceiling is set at i=10, so the maximum delay is 1023 slot times.