After a collision, if all devices retry immediately, they’ll collide again. A randomized waiting mechanism is needed to reduce the probability of repeated collisions.
An algorithm where the maximum random wait time doubles after each successive collision, reducing retry attempts when the network is congested.
- First collision: wait random time between 0 and 1 slot time
- Second collision: wait random time between 0 and 2 slot times
- Third collision: wait random time between 0 and 4 slot times
- Nth collision: wait random time between 0 and 2^N slot times (capped at 1024)
- After successful transmission, the backoff counter resets
- Reduces collision probability under high load
- Wait time grows exponentially with repeated collisions
- Capped at maximum backoff (e.g., 1024 slots in Ethernet)
- Used in CSMA/CD and some wireless protocols
- Built from: CD — uses this backoff algorithm
- Related: Collision — triggers backoff
- Related: Jam Signal — sent before backoff
- Related: Random Access — broader category of protocols using backoff
- Maximum backoff limit prevents excessive wait times
- Many collisions can still cause long delays (exponential growth)
- Not used in modern full-duplex Ethernet (no collisions to back off from)