The Flow Queue CoDel Packet Scheduler and Active Queue Management Algorithm
RFC 8290

Document Type RFC - Experimental (January 2018; No errata)
Last updated 2018-01-05
Replaces draft-hoeiland-joergensen-aqm-fq-codel
Stream IETF
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Reviews
Stream WG state Submitted to IESG for Publication
Document shepherd Wesley Eddy
Shepherd write-up Show (last changed 2016-02-14)
IESG IESG state RFC 8290 (Experimental)
Consensus Boilerplate Yes
Telechat date
Responsible AD Martin Stiemerling
Send notices to (None)
IANA IANA review state Version Changed - Review Needed
IANA action state No IC
Internet Engineering Task Force (IETF)            T. Hoeiland-Joergensen
Request for Comments: 8290                           Karlstad University
Category: Experimental                                       P. McKenney
ISSN: 2070-1721                              IBM Linux Technology Center
                                                                 D. Taht
                                                                Teklibre
                                                               J. Gettys

                                                              E. Dumazet
                                                            Google, Inc.
                                                            January 2018

               The Flow Queue CoDel Packet Scheduler and
                   Active Queue Management Algorithm

Abstract

   This memo presents the FQ-CoDel hybrid packet scheduler and Active
   Queue Management (AQM) algorithm, a powerful tool for fighting
   bufferbloat and reducing latency.

   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.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8290.

Hoeiland-Joergensen, et al.   Experimental                      [Page 1]
RFC 8290                        FQ-CoDel                    January 2018

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Hoeiland-Joergensen, et al.   Experimental                      [Page 2]
RFC 8290                        FQ-CoDel                    January 2018

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   4
     1.2.  Terminology and Concepts  . . . . . . . . . . . . . . . .   5
     1.3.  Informal Summary of FQ-CoDel  . . . . . . . . . . . . . .   5
   2.  CoDel . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Flow Queueing . . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  The FQ-CoDel Scheduler  . . . . . . . . . . . . . . . . . . .   8
     4.1.  Enqueue . . . . . . . . . . . . . . . . . . . . . . . . .   8
       4.1.1.  Alternative Classification Schemes  . . . . . . . . .   9
     4.2.  Dequeue . . . . . . . . . . . . . . . . . . . . . . . . .  10
   5.  Implementation Considerations . . . . . . . . . . . . . . . .  11
     5.1.  Data Structures . . . . . . . . . . . . . . . . . . . . .  11
     5.2.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .  12
       5.2.1.  Interval  . . . . . . . . . . . . . . . . . . . . . .  12
       5.2.2.  Target  . . . . . . . . . . . . . . . . . . . . . . .  12
       5.2.3.  Packet Limit  . . . . . . . . . . . . . . . . . . . .  13
       5.2.4.  Quantum . . . . . . . . . . . . . . . . . . . . . . .  13
       5.2.5.  Flows . . . . . . . . . . . . . . . . . . . . . . . .  13
       5.2.6.  Explicit Congestion Notification (ECN)  . . . . . . .  14
       5.2.7.  CE Threshold  . . . . . . . . . . . . . . . . . . . .  14
     5.3.  Probability of Hash Collisions  . . . . . . . . . . . . .  14
     5.4.  Memory Overhead . . . . . . . . . . . . . . . . . . . . .  15
     5.5.  Per-Packet Timestamping . . . . . . . . . . . . . . . . .  16
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