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From: tcp-ip@ucbvax.ARPA
Newsgroups: fa.tcp-ip
Subject: Re: TCP Timer
Message-ID: <8198@ucbvax.ARPA>
Date: Sat, 15-Jun-85 07:07:34 EDT
Article-I.D.: ucbvax.8198
Posted: Sat Jun 15 07:07:34 1985
Date-Received: Sun, 16-Jun-85 00:41:44 EDT
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Organization: University of California at Berkeley
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From: CERF@USC-ISI.ARPA

Lixia,

I can't offer any statistics on other implementations, but one would
expect that a timer for the segment at the head of the queue for
any paritcular connection would be sufficient. If that segment times
oout, you retransmit it and perhaps you look to see if any other
segments on the queue have timed out.  When the acknowledgement is
received, you reset the timer for the next segment in the queue
if it has not also been acknowledged.

The calculation of the proper timeout in a variable delay 
environment is a challenge. Perhaps Dave Mills has the most experience
in devising ways to cope with varying transmission and propagation
delays.  Others have experimented with solutions to this problem and
I trust they will also respond to your query.  You might also read 
some of Dave Clark's notes to implementors on the subject of handling
retransmission.

Vint Cerf