rLEDBAT: receiver-driven Low Extra Delay Background Transport for TCP
draft-irtf-iccrg-rledbat-01
Network Working Group M. Bagnulo
Internet-Draft A. Garcia-Martinez
Intended status: Experimental UC3M
Expires: February 26, 2021 G. Montenegro
P. Balasubramanian
Microsoft
August 25, 2020
rLEDBAT: receiver-driven Low Extra Delay Background Transport for TCP
draft-irtf-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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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 . . . . . . . . . . . . . . . . . 6
3.2. Measuring delays . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Measuring the RTT to estimate the queueing delay . . 7
3.2.2. Measuring one way delay to estimate the queueing
delay . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3. Detecting packet losses and retransmissions . . . . . . . 12
4. Security Considerations . . . . . . . . . . . . . . . . . . . 12
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
7. Informative References . . . . . . . . . . . . . . . . . . . 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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