CoDel - The Controlled-Delay Active Queue Management algorithm.

Explanations for the average person:

  • measure the latency in the queue (from ingress to egress, via time stamping on entry and checking the timestamp on exit
  • when latency exceeds tartget, think about dropping a packet
  • after latency exceeds target, drop a packet at the HEAD of the queue (not the tail!)
  • if that does not fix it, after a shorter interval (inverse sqrt), drop the net packet sooner, again at the HEAD
  • keep decreasing the interval between drops until the latency in the queue drops below target
  • we start with 100ms at the interval of the estimate and 5ms as the target (for 4Mbit/s and up); 10Gb/s needs a smaller target.
  • below 4Mbit/s ... well, we don't know
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  • Last modified: 2023/06/18 12:00
  • by tatami