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Limited Slow-Start for TCP with Large Congestion Windows (RFC3742)

IP.com Disclosure Number: IPCOM000023316D
Original Publication Date: 2004-Mar-01
Included in the Prior Art Database: 2004-Mar-30
Document File: 8 page(s) / 15K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

S. Floyd: AUTHOR

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.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 22% of the total text.

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 [Page 1]

RFC 3742 TCP's Slow-Start with Large Congestion Windows March 2004

congestion window is increased for one window of data during slow-

start, in order to improve performance for TCP connections with large

congestion windows.

When slow-start results in a large increase in the congestion window

in one round-trip time, a large number of packets might be dropped in

the network (even with carefully-tuned active queue management

mechanisms in the routers). This drop of a large number of packets

in the network can result in unnecessary retransmit timeouts for the

TCP connection. The TCP connection could end up in the congestion

avoidance phase with a very small congestion window, and could take a

large number of round-trip times to recover its old congestion

window. This poor performance is illustrated i...