backoff

Backoff is a delay strategy used to reduce contention, congestion, or repeated failures by intentionally delaying subsequent actions after an unsuccessful attempt. It is commonly employed in communication protocols, retry mechanisms, and load management to improve stability and fairness.

In networking, backoff is central to collision avoidance in shared-channel protocols such as Ethernet with CSMA/CD and wireless networks. When devices transmit simultaneously and a collision occurs, each device waits for a random period before retrying. The waiting time is determined by a contention window (CW) that increases after each collision, typically via exponential backoff. The backoff interval is a random value within the current CW, multiplied by a basic time unit called the slot time. This mechanism reduces the probability of repeated collisions as traffic escalates.

In software and distributed systems, backoff appears in retry policies for transient errors or rate limits. After a failed operation, a system waits before retrying, with the delay often following a linear or exponential progression. Exponential backoff is common, sometimes augmented with jitter to desynchronize concurrent retries. Backoff helps prevent thundering herds and aids stability under heavy load or bursty failures. Practical considerations include setting a maximum number of retries, a cap on the backoff duration, and incorporating jitter to avoid synchronized retries.

Other domains use backoff in APIs and queues, where clients observe Retry-After hints or backoff during polling. The term is also used in rate limiting and admission control to gradually restore acceptable load. See also: exponential backoff, jitter, CSMA/CD, retry policy.