Active queue management

Active queue management, abbreviated AQM, is a family of policies that routers and switches use to drop or mark packets inside a buffer before the buffer fills completely. The aim is to reduce network congestion and improve end-to-end latency. Older routers used a drop-tail discipline, accepting packets until the queue reached its maximum length and discarding the rest, which penalises bursty flows and can synchronise many flows at once. AQM disciplines instead keep one or more drop or mark probabilities and act on packets according to them, which gives endpoints an early congestion signal and holds queues shorter, countering bufferbloat. Early disciplines such as random early detection and SRED need careful parameter tuning, while modern ones including ARED, Blue, PI, CoDel and CAKE are self-tuning. The network scheduler applies these algorithms, and RFC 7567 recommends AQM as a best practice.