rLEDBAT: receiver-driven Low Extra Delay Background Transport for TCP
draft-bagnulo-iccrg-rledbat-01

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Network Working Group                                         M. Bagnulo
Internet-Draft                                        A. Garcia-Martinez
Intended status: Experimental                                       UC3M
Expires: May 1, 2020                                       G. Montenegro
                                                      P. Balasubramanian
                                                               Microsoft
                                                        October 29, 2019

 rLEDBAT: receiver-driven Low Extra Delay Background Transport for TCP
                   draft-bagnulo-iccrg-rledbat-01.txt

Abstract

   This document specifies the rLEDBAT, a set of mechanisms that enable
   the execution of a less-than-best-effort congestion control algorithm
   for TCP at the receiver end.

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   Copyright (c) 2019 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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Motivations for rLEDBAT . . . . . . . . . . . . . . . . . . .   3
   3.  rLEDBAT mechanisms  . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Controlling the receive window  . . . . . . . . . . . . .   5
       3.1.1.  Avoiding window shrinking . . . . . . . . . . . . . .   6
       3.1.2.  Window Scale Option . . . . . . . . . . . . . . . . .   7
     3.2.  Measuring the Round Trip Time . . . . . . . . . . . . . .   7
       3.2.1.  Measuring the RTT to estimate the queueing delay  . .   8
     3.3.  Detecting retransmissions and packet losses . . . . . . .  10
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   7.  Informative References  . . . . . . . . . . . . . . . . . . .  11
   Appendix A.  Difficulties while measuring one way delay at the
                TCP receiver . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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
   sending rate.  LEDBAT estimates the queuing delay by subtracting the
   measured current one-way delay from the estimated base one-way delay
   (i.e. the one-way delay in the absence of queues).

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