backoffs

Backoff is a strategy used to introduce a delay before retrying an operation after a failure or a collision. The goal is to reduce contention for shared resources, prevent repeated collisions, and stabilize system throughput.

Backoff is widely used in computer networks (for example Ethernet and wireless LANs) and in distributed software systems that perform retries against a remote service or queue. In networks, backoff timers help avoid simultaneous transmissions; in software, they temper retry rates to cope with transient failures.

Common backoff schemes include fixed, linear, exponential, and randomized backoff. In randomized/exponential backoff, a node selects a random wait within a contention window whose size grows after each failure.

Binary Exponential Backoff (BEB) is a specific scheme used in Ethernet LANs: after a collision, each station waits a random number of time slots from 0 to 2^k − 1, where k is the number of collisions for that frame, up to a maximum limit.

In transport protocols such as TCP, backoff is applied to retransmission timeouts; the retransmission timeout often grows multiplicatively (exponential backoff) after successive timeouts. In practice, jitter is added to spread out retries and mitigate synchronized bursts.

Key considerations include choosing minimum and maximum backoff values, handling non-idempotent operations, and preventing thundering herd effects. Backoff strategies trade latency for stability and efficiency; inappropriate settings can lead to starvation or excessive delay.