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Quick-Start for TCP and IP
RFC 4782

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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