rLEDBAT: receiver-driven Low Extra Delay Background Transport for TCP
draft-bagnulo-iccrg-rledbat-00

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Network Working Group                                         M. Bagnulo
Internet-Draft                                        A. Garcia-Martinez
Intended status: Experimental                                       UC3M
Expires: January 9, 2020                                   G. Montenegro
                                                      P. Balasubramanian
                                                               Microsoft
                                                            July 8, 2019

 rLEDBAT: receiver-driven Low Extra Delay Background Transport for TCP
                   draft-bagnulo-iccrg-rledbat-00.txt

Abstract

   This document specifies the rLEDBAT, a receiver-driven, less-than-
   best-effort congestion control algorithm for TCP.

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   Copyright (c) 2019 IETF Trust and the persons identified as the
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Bagnulo, et al.          Expires January 9, 2020                [Page 1]
Internet-Draft                   rLEDBAT                       July 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Motivations for rLEDBAT . . . . . . . . . . . . . . . . . . .   3
   3.  rLEDBAT overview  . . . . . . . . . . . . . . . . . . . . . .   4
   4.  rLEDBAT design rationale  . . . . . . . . . . . . . . . . . .   5
     4.1.  Controlling the receive window  . . . . . . . . . . . . .   5
       4.1.1.  Avoiding window shrinking . . . . . . . . . . . . . .   6
       4.1.2.  Window Scale Option . . . . . . . . . . . . . . . . .   6
     4.2.  Using the RTT to estimate the queueing delay  . . . . . .   7
     4.3.  Inter-rLEDBAT fairness  . . . . . . . . . . . . . . . . .   9
     4.4.  Reacting to packet loss . . . . . . . . . . . . . . . . .   9
     4.5.  Bootstrapping . . . . . . . . . . . . . . . . . . . . . .  10
     4.6.  Reaction to path changes  . . . . . . . . . . . . . . . .  11
   5.  rLEDBAT algorithm . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Data structures . . . . . . . . . . . . . . . . . . . . .  11
     5.2.  Algorithm . . . . . . . . . . . . . . . . . . . . . . . .  12
     5.3.  rLEDBAT parameters  . . . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   LEDBAT (Low Extra Delay Background Transport) [RFC6817] is a
   congestion-control algorithm that implements a less-than-best-effort
   (LBE) traffic class.

   When LEDBAT traffic shares a bottleneck with one or more TCP
   connections using standard congestion control algorithms such as
   Cubic [RFC8312] (hereafter standard-TCP for short), it reduces its
   sending rate earlier and more aggressively than standard-TCP
   congestion control, allowing standard-TCP traffic to use more of the
   available capacity.  In the absence of competing standard-TCP
   traffic, LEDBAT aims to make an efficient use of the available
   capacity, while keeping the queuing delay within predefined bounds.

   LEDBAT reacts both to packet loss and to variations in delay.
   Regarding to packet loss, LEDBAT reacts with a multiplicative
   decrease, similar to most TCP congestion controllers.  Regarding
   delay, LEDBAT aims for a target queueing delay.  When the measured
   current queueing delay is below the target, LEDBAT increases the
   sending rate and when the delay is above the target, it reduces the