FlowQueue-Codel
draft-ietf-aqm-fq-codel-01

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Last updated 2015-10-14 (latest revision 2015-07-04)
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AQM working group                                 T. Hoeiland-Joergensen
Internet-Draft                                       Karlstad University
Intended status: Informational                               P. McKenney
Expires: January 5, 2016                     IBM Linux Technology Center
                                                                 D. Taht
                                                                Teklibre
                                                               J. Gettys

                                                              E. Dumazet
                                                            Google, Inc.
                                                           July 04, 2015

                            FlowQueue-Codel
                       draft-ietf-aqm-fq-codel-01

Abstract

   This memo presents the FQ-CoDel hybrid packet scheduler/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 Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 5, 2016.

Hoeiland-Joergensen, et aExpires January 5, 2016                [Page 1]
Internet-Draft                  fq-codel                       July 2015

Copyright Notice

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology and concepts  . . . . . . . . . . . . . . . .   3
     1.2.  Informal summary of FQ-CoDel  . . . . . . . . . . . . . .   4
   2.  CoDel . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Flow Queueing . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  FQ-CoDel Parameters and Data Structures . . . . . . . . . . .   6
     4.1.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .   6
       4.1.1.  Interval  . . . . . . . . . . . . . . . . . . . . . .   6
       4.1.2.  Target  . . . . . . . . . . . . . . . . . . . . . . .   7
       4.1.3.  Packet limit  . . . . . . . . . . . . . . . . . . . .   7
       4.1.4.  Quantum . . . . . . . . . . . . . . . . . . . . . . .   7
       4.1.5.  Flows . . . . . . . . . . . . . . . . . . . . . . . .   8
       4.1.6.  ECN . . . . . . . . . . . . . . . . . . . . . . . . .   8
       4.1.7.  CE_THRESHOLD  . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Data structures . . . . . . . . . . . . . . . . . . . . .   8
       4.2.1.  Internal queues . . . . . . . . . . . . . . . . . . .   8
       4.2.2.  New and old queues lists  . . . . . . . . . . . . . .   9
   5.  The FQ-CoDel scheduler  . . . . . . . . . . . . . . . . . . .   9
     5.1.  Enqueue . . . . . . . . . . . . . . . . . . . . . . . . .   9
       5.1.1.  Alternative classification schemes  . . . . . . . . .  10
     5.2.  Dequeue . . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Implementation considerations . . . . . . . . . . . . . . . .  11
     6.1.  Probability of hash collisions  . . . . . . . . . . . . .  11
     6.2.  Memory Overhead . . . . . . . . . . . . . . . . . . . . .  12
     6.3.  Per-Packet Timestamping . . . . . . . . . . . . . . . . .  13
     6.4.  Other forms of "Fair Queueing"  . . . . . . . . . . . . .  13
     6.5.  Differences between CoDel and FQ-CoDel behaviour  . . . .  13
   7.  Limitations of flow queueing  . . . . . . . . . . . . . . . .  14
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