Network Working Group S. Floyd
Request for Comments: 4782 M. Allman
Category: Experimental ICIR
A. Jain
F5 Networks
P. Sarolahti
Nokia Research Center
January 2007
Quick-Start for TCP and IP
Status of This Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document specifies an optional Quick-Start mechanism for
transport protocols, in cooperation with routers, to determine an
allowed sending rate at the start and, at times, in the middle of a
data transfer (e.g., after an idle period). While Quick-Start is
designed to be used by a range of transport protocols, in this
document we only specify its use with TCP. Quick-Start is designed
to allow connections to use higher sending rates when there is
significant unused bandwidth along the path, and the sender and all
of the routers along the path approve the Quick-Start Request.
This document describes many paths where Quick-Start Requests would
not be approved. These paths include all paths containing routers,
IP tunnels, MPLS paths, and the like that do not support Quick-
Start. These paths also include paths with routers or middleboxes
that drop packets containing IP options. Quick-Start Requests could
be difficult to approve over paths that include multi-access layer-
two networks. This document also describes environments where the
Quick-Start process could fail with false positives, with the sender
incorrectly assuming that the Quick-Start Request had been approved
by all of the routers along the path. As a result of these concerns,
and as a result of the difficulties and seeming absence of motivation
for routers, such as core routers to deploy Quick-Start, Quick-Start
is being proposed as a mechanism that could be of use in controlled
Floyd, et al. Experimental [Page 1]RFC 4782 Quick-Start for TCP and IP January 2007
environments, and not as a mechanism that would be intended or
appropriate for ubiquitous deployment in the global Internet.
Table of Contents
1. Introduction ....................................................4
1.1. Conventions and Terminology ................................5
2. Assumptions and General Principles ..............................6
2.1. Overview of Quick-Start ....................................7
3. The Quick-Start Option in IP ...................................10
3.1. The Quick-Start Option for IPv4 ...........................10
3.2. The Quick-Start Option for IPv6 ...........................13
3.3. Processing the Quick-Start Request at Routers .............14
3.3.1. Processing the Report of Approved Rate .............15
3.4. The QS Nonce ..............................................16
4. The Quick-Start Mechanisms in TCP ..............................18
4.1. Sending the Quick-Start Request ...........................19
4.2. The Quick-Start Response Option in the TCP header .........20
4.3. TCP: Sending the Quick-Start Response .....................21
4.4. TCP: Receiving and Using the Quick-Start Response Packet ..22
4.5. TCP: Controlling Acknowledgement Traffic on the
Reverse Path ..............................................24
4.6. TCP: Responding to a Loss of a Quick-Start Packet .........26
4.7. TCP: A Quick-Start Request for a Larger Initial Window ....26
4.7.1. Interactions with Path MTU Discovery ...............26
4.7.2. Quick-Start Request Packets that are
Discarded by Routers or Middleboxes ................27
4.8. TCP: A Quick-Start Request in the Middle of a Connection ..28
4.9. An Example Quick-Start Scenario with TCP ..................29
5. Quick-Start and IPsec AH .......................................30
6. Quick-Start in IP Tunnels and MPLS .............................31
6.1. Simple Tunnels that Are Compatible with Quick-Start .......33
6.1.1. Simple Tunnels that Are Aware of Quick-Start .......33
6.2. Simple Tunnels that Are Not Compatible with Quick-Start ...34
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