Prague Congestion Control
draft-briscoe-iccrg-prague-congestion-control-00

Document Type Active Internet-Draft (individual)
Authors Koen De Schepper  , Olivier Tilmans  , Bob Briscoe 
Last updated 2021-03-09
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Internet Congestion Control Research Group (ICCRG)        K. De Schepper
Internet-Draft                                                O. Tilmans
Intended status: Experimental                            Nokia Bell Labs
Expires: September 10, 2021                              B. Briscoe, Ed.
                                                             Independent
                                                           March 9, 2021

                       Prague Congestion Control
            draft-briscoe-iccrg-prague-congestion-control-00

Abstract

   This specification defines the Prague congestion control scheme,
   which is derived from DCTCP and adapted for Internet traffic by
   implementing the Prague L4S requirements.  Over paths with L4S
   support at the bottleneck, it adapts the DCTCP mechanisms to achieve
   consistently low latency and full throughput.  It is defined
   independently of any particular transport protocol or operating
   system, but notes are added that highlight issues specific to certain
   transports and OSs.  It is mainly based on the current default
   options of the reference Linux implementation of TCP Prague, but it
   includes experience from other implementations where available.  It
   separately describes non-default and optional parts, as well as
   future plans.

   The implementation does not satisfy all the Prague requirements (yet)
   and the IETF might decide that certain requirements need to be
   relaxed as an outcome of the process of trying to satisfy them all.
   In two cases, research code is replaced by placeholders until full
   evaluation is complete.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 10, 2021.

De Schepper, et al.    Expires September 10, 2021               [Page 1]
Internet-Draft          Prague Congestion Control             March 2021

Copyright Notice

   Copyright (c) 2021 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Motivation: Low Queuing Delay /and/ Full Throughput . . .   4
     1.2.  Document Purpose  . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Maturity Status (To be Removed Before Publication)  . . .   5
     1.4.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
   2.  Prague Congestion Control . . . . . . . . . . . . . . . . . .   8
     2.1.  The Prague L4S Requirements . . . . . . . . . . . . . . .   8
     2.2.  Packet Identification . . . . . . . . . . . . . . . . . .  10
     2.3.  Detecting and Measuring Congestion  . . . . . . . . . . .  10
       2.3.1.  Accurate ECN Feedback . . . . . . . . . . . . . . . .  10
         2.3.1.1.  Accurate ECN Feedback with TCP & Derivatives  . .  11
         2.3.1.2.  Accurate ECN Feedback with Other Modern
                   Transports  . . . . . . . . . . . . . . . . . . .  11
       2.3.2.  Moving Average of ECN Feedback  . . . . . . . . . . .  12
       2.3.3.  Scaling Loss Detection with Flow Rate . . . . . . . .  13
     2.4.  Congestion Response Algorithm . . . . . . . . . . . . . .  13
       2.4.1.  Fall-Back on Loss . . . . . . . . . . . . . . . . . .  13
       2.4.2.  Multiplicative Decrease on ECN Feedback . . . . . . .  14
       2.4.3.  Additive Increase and ECN Feedback  . . . . . . . . .  15
       2.4.4.  Reduced RTT-Dependence  . . . . . . . . . . . . . . .  16
       2.4.5.  Flow Start or Restart . . . . . . . . . . . . . . . .  17
     2.5.  Packet Sending  . . . . . . . . . . . . . . . . . . . . .  18
       2.5.1.  Packet Pacing . . . . . . . . . . . . . . . . . . . .  18
       2.5.2.  Segmentation Offload  . . . . . . . . . . . . . . . .  18
   3.  Variants and Future Work  . . . . . . . . . . . . . . . . . .  19
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