RFC 3742 (rfc3742) - Page 1 of 7

Limited Slow-Start for TCP with Large Congestion Windows

Network Working Group                                           S. Floyd
Request for Comments: 3742                                          ICSI
Category: Experimental                                        March 2004


        Limited Slow-Start for TCP with Large Congestion Windows

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 Internet Society (2004).  All Rights Reserved.

Abstract

   This document describes an optional modification for TCP's slow-start
   for use with TCP connections with large congestion windows.  For TCP
   connections that are able to use congestion windows of thousands (or
   tens of thousands) of MSS-sized segments (for MSS the sender's
   MAXIMUM SEGMENT SIZE), the current slow-start procedure can result in
   increasing the congestion window by thousands of segments in a single
   round-trip time.  Such an increase can easily result in thousands of
   packets being dropped in one round-trip time.  This is often
   counter-productive for the TCP flow itself, and is also hard on the
   rest of the traffic sharing the congested link.  This note describes
   Limited Slow-Start as an optional mechanism for limiting the number
   of segments by which the congestion window is increased for one
   window of data during slow-start, in order to improve performance for
   TCP connections with large congestion windows.

1.  Introduction

   This note describes an optional modification for TCP's slow-start for
   use with TCP connections with large congestion windows.  For TCP
   connections that are able to use congestion windows of thousands (or
   tens of thousands) of MSS-sized segments (for MSS the sender's
   MAXIMUM SEGMENT SIZE), the current slow-start procedure can result in
   increasing the congestion window by thousands of segments in a single
   round-trip time.  Such an increase can easily result in thousands of
   packets being dropped in one round-trip time.  This is often
   counter-productive for the TCP flow itself, and is also hard on the
   rest of the traffic sharing the congested link.  This note describes
   Limited Slow-Start, limiting the number of segments by which the



Floyd                         Experimental