Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 alpha 4/15/85; site ucbvax.ARPA
Path: utzoo!watmath!clyde!cbosgd!ucbvax!tcp-ip
From: tcp-ip@ucbvax.ARPA
Newsgroups: fa.tcp-ip
Subject: Re: TCP Timer
Message-ID: <8202@ucbvax.ARPA>
Date: Sat, 15-Jun-85 14:39:48 EDT
Article-I.D.: ucbvax.8202
Posted: Sat Jun 15 14:39:48 1985
Date-Received: Sun, 16-Jun-85 01:16:46 EDT
Sender: daemon@ucbvax.ARPA
Organization: University of California at Berkeley
Lines: 25

From: MILLS@USC-ISID.ARPA

In response to the message sent  15 Jun 1985 06:40-EDT from CERF@USC-ISI.ARPA

Vint,

The problem of estimating the mean of the roundtrip-delay random variable
was discussed in RFC-889. The so-called "RSRE algorithm," which we have
been using for several years, provides only a single sample per roundtrip
interval, which is appropriate for retransmission policies in which only the
first wadge on the retransmission queue is retransmitted. However, convergence
to a good mean-estimate is accellerated if you keep separate timers for
each segment originally transmitted and update the estimate with a new sample
as the ACK-sequence number passes by the first octet of the corresponding
segment, even if the segment timer isn't used for anything else. Under
conditions where many segments can be in flight, the estimate is very much
improved. The estimate can be improved further using a nonlinear smoothing
algorithm, as discussed in RFC-889.

All this horsepower was found necessary for a pair of fuzzballs to grumble
to each other via a transatlantic-cable link using a statistical multiplexor.
The delay variance on that circuit you wouldn't believe!

Dave
-------