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TCP Congestion Window Validation (RFC2861)

IP.com Disclosure Number: IPCOM000003461D
Original Publication Date: 2000-Jun-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 9 page(s) / 25K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

M. Handley: AUTHOR [+3]

Abstract

TCP's congestion window controls the number of packets a TCP flow may have in the network at any time. However, long periods when the sender is idle or application-limited can lead to the invalidation of the congestion window, in that the congestion window no longer reflects current information about the state of the network. This document describes a simple modification to TCP's congestion control algorithms to decay the congestion window cwnd after the transition from a sufficiently-long application-limited period, while using the slow-start threshold ssthresh to save information about the previous value of the congestion window.

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 11% of the total text.

Network Working Group M. Handley

Request for Comments: 2861 J. Padhye

Category: Experimental S. Floyd

ACIRI

June 2000

TCP Congestion Window Validation

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 (2000). All Rights Reserved.

Abstract

TCP's congestion window controls the number of packets a TCP flow may

have in the network at any time. However, long periods when the

sender is idle or application-limited can lead to the invalidation of

the congestion window, in that the congestion window no longer

reflects current information about the state of the network. This

document describes a simple modification to TCP's congestion control

algorithms to decay the congestion window cwnd after the transition

from a sufficiently-long application-limited period, while using the

slow-start threshold ssthresh to save information about the previous

value of the congestion window.

An invalid congestion window also results when the congestion window

is increased (i.e., in TCP's slow-start or congestion avoidance

phases) during application-limited periods, when the previous value

of the congestion window might never have been fully utilized. We

propose that the TCP sender should not increase the congestion window

when the TCP sender has been application-limited (and therefore has

not fully used the current congestion window). We have explored

these algorithms both with simulations and with experiments from an

implementation in FreeBSD.

1. Conventions and Acronyms

The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,

SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this

document, are to be interpreted as described in [B97].

2. Introduction

TCP's congestion window controls the number of packets a TCP flow may

have in the network at any time. The congestion window is set using

an Additive-Increase, Multiplicative-Decrease (AIMD) mechanism that

probes for available bandwidth, dynamically adapting to changing

network conditions. This AIMD mechanism works well when the sender

continually has data to send, as is typically the case for TCP used<...