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dummynet – flexible bandwidth manager and delay emulator

Some terms:

• AQM - Active Queue Management
  • droptail - drop packetss if full
  • CoDel
  • PIE

• pipe (link, limiter)- virtual path that emulates a connection with a specified bandwidth, propagation delay, and packet loss pattern.
• scheduler - arbitrate access of multiple flows to the same link (pipe)
  • FIFO
  • DRR
  • PRIO
  • WF2Q+
  • QFQ
  • KPS

• Simple pipe internally has attached
  • queue (droptail)
  • scheduler (FIFO)
  • pipe (a link emulator with given badwidth and delay)

• Pipe with CoDel AQM set
  • queue is a dummy queue without any management policy (no droptail). It is not used to buffer incoming packets
  • CoDel scheduler manages internal queues to buffer packets

REMARKS:

• CoDel on queues is ignored when fq-codel is enabled on pipe.
  • queue is needed (even if not really used). There is no other way to send packets to fq-codel scheduler. So creating a pipe with fq-codel will always create a queue.
• number of internal queues in fq-codel is condifured by flows parameter