====== Traffic Shaper ======

[[https://www.freebsd.org/cgi/man.cgi?query=dummynet&apropos=0&sektion=0&manpath=FreeBSD+11.2-RELEASE&arch=default&format=html|dummynet]] -- flexible bandwidth manager and delay emulator
[[http://caia.swin.edu.au/reports/160708A/CAIA-TR-160708A.pdf]]

Some terms:

  * **AQM** - **A**ctive **Q**ueue **M**anagement
    * **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)
{{:sw:opnsense:fig5_a_simple_dummynet_pipe.jpg?400|}}

===== FQ-CoDel =====
The **FlowQueue-CoDel** (**FQ-CoDel**) algorithm is a combined packet scheduler and Active Queue Management (AQM) algorithm.

  * Pipe with fq-CoDel AQM set
      * queue is a dummy queue without any management policy (no droptail). It is not used to buffer incoming packets
      * fq-CoDel scheduler manages internal queues to buffer packets
{{:sw:opnsense:fig7_fq_codel.jpg?400|}}


REMARKS:
  * **fq-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



===== shell =====

<code bash>
ipfw pipe show
ipfw sched show
ipfw queue show
</code>