RFC 2861 (rfc2861) - Page 1 of 11

TCP Congestion Window Validation

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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].



Handley, et al.               Experimental
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