Skip to main content

The Flow Queue CoDel Packet Scheduler and Active Queue Management Algorithm

Approval announcement
Draft of message to be sent after approval:


From: The IESG <>
To: "IETF-Announce" <>
Cc:,,,, "The IESG" <>,,
Subject: Document Action: 'The FlowQueue-CoDel Packet Scheduler and Active Queue Management Algorithm' to Experimental RFC (draft-ietf-aqm-fq-codel-06.txt)

The IESG has approved the following document:
- 'The FlowQueue-CoDel Packet Scheduler and Active Queue Management
  (draft-ietf-aqm-fq-codel-06.txt) as Experimental RFC

This document is the product of the Active Queue Management and Packet
Scheduling Working Group.

The IESG contact persons are Spencer Dawkins and Martin Stiemerling.

A URL of this Internet Draft is:

Ballot Text

Technical Summary

   This memo presents the FQ-CoDel hybrid packet scheduler/AQM
   algorithm, a powerful tool for fighting bufferbloat and reducing

   FQ-CoDel mixes packets from multiple flows and reduces the impact of
   head of line blocking from bursty traffic.  It provides isolation for
   low-rate traffic such as DNS, web, and videoconferencing traffic.  It
   improves utilisation across the networking fabric, especially for
   bidirectional traffic, by keeping queue lengths short; and it can be
   implemented in a memory- and CPU-efficient fashion across a wide
   range of hardware.

Working Group Summary

An interesting aspect of this document is the combined use of CoDel with 
FQ for improving flow-isolation properties. The working group had early 
discussions about the differences between FQ and scheduling mechanisms 
versus more pure AQM algorithms (like CoDel).  This resulted in draft-
ietf-aqm-fq-implementation, which describes the terminology and 
construction of hybrid systems.  Any early disagreement in the WG about 
this seems to have subsided after the subsequent discussions and work to 
resolve terminology and scope.

Document Quality

Yes, there are existing implementations and deployments, including in 
the Linux kernel.  There have been other implementation efforts in 
addition to the editors, and questions have been shared on the AQM 
mailing list, with clarifications posted in draft updates.  The Linux 
implementation is from the editors of the document, and an independent 
implementation in FreeBSD was done by Rasool As-Saadi at the Swinburne 


Wes Eddy ( is the Document Shepherd.  Martin 
Stiemerling is the responsible AD.

RFC Editor Note