Proportional Rate Reduction for TCP
draft-mathis-tcpm-rfc6937bis-00

Document Type Active Internet-Draft (individual)
Authors Matt Mathis  , Nandita Dukkipati  , Yuchung Cheng 
Last updated 2020-11-01
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TCP Maintenance Working Group                                  M. Mathis
Internet-Draft                                              N. Dukkipati
Obsoletes: 6937 (if approved)                                   Y. Cheng
Intended status: Standards Track                            Google, Inc.
Expires: 4 May 2021                                      31 October 2020

                  Proportional Rate Reduction for TCP
                    draft-mathis-tcpm-rfc6937bis-00

Abstract

   This document updates the Proportional Rate Reduction (PRR) algorithm
   described as experimental in RFC 6937 to standards track.  PRR
   potentially replaces the Fast Recovery and Rate-Halving algorithms.
   All of these algorithms regulate the amount of data sent by TCP or
   other transport protocol during loss recovery.  PRR more accurately
   regulates the actual flight size through recovery such that at the
   end of recovery it will be as close as possible to the ssthresh, as
   determined by the congestion control algorithm.

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Mathis, et al.             Expires 4 May 2021                   [Page 1]
Internet-Draft         Proportional Rate Reduction          October 2020

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Algorithms  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Properties  . . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Measurements  . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Conclusion and Recommendations  . . . . . . . . . . . . . . .  11
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  12
   10. Informative References  . . . . . . . . . . . . . . . . . . .  13
   Appendix A.  Strong Packet Conservation Bound . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   This document updates the Proportional Rate Reduction (PRR) algorithm
   described in [RFC6937]from experimental to standards track.  PRR
   accuracy regulates the amount of data sent during loss recovery, such
   that at the end of recovery the flight size will be as close as
   possible to the ssthresh, as determined by the congestion control
   algorithm.  PRR has been deployed in at least 3 major operating
   systems covering the vast majority of today's web traffic.  There
   have been no changes to PRR as documented in the experimental RFC.
   The descriptions here have been [will be] updated to normative
   standards language.  For a tutorial description of the algorithms and
   the rationale behind them please see the original RFC.

   The experimental RFC describes two different reduction bound
   algorithms to limit the total window reduction due to all mechanisms,
   including transient application stalls and the losses themselves:
   Conservative Reduction Bound (CRB), which is strictly packet
   conserving; and a Slow Start Reduction Bound (SSRB), which is more
   aggressive than CRB by at most 1 segment per ACK.  [RFC6937] left the
   choice of Reduction Bound to the discretion of the implementer.

   The paper "An Internet-Wide Analysis of Traffic Policing" [Flatch et
   al] uncovered a crucial situation where the Reduction Bound mattered.
   Under certain configurations, token bucket traffic policers
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