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        RFC 2861

        Title:      TCP Congestion Window Validation
        Author(s):  M. Handley, J. Padhye, S. Floyd
        Status:     Experimental
        Date:       June 2000
        Mailbox:    mjh@aciri.org, padhye@aciri.org, floyd@aciri.org 
        Pages:      11
        Characters: 26993
        Updates/Obsoletes/SeeAlso:    None

        I-D Tag:    draft-handley-tcp-cwv-02.txt

        URL:        ftp://ftp.isi.edu/in-notes/rfc2861.txt


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.

This document is a product of the Transport Area Working Group of the
IETF.

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
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