Re: Does tcptrace measure RTT for every ACK?

From: Mark Allman (mallman@grc.nasa.gov)
Date: 11/14/02

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Message-Id: <200211150422.gAF4MNJg020386@thoth.ir.bbn.com>
From: Mark Allman <mallman@grc.nasa.gov>
Subject: Re: Does tcptrace measure RTT for every ACK? 
Date: Thu, 14 Nov 2002 23:22:23 -0500

> As you know, the TCP measurement is made every RTT, not for
> every ACK, in the real world.

Depends on which real world you're talking about. Traditionally,
TCP has always timed one segment and its corresponding ACK at a
time. However, if a TCP uses timestamps and the RTTM algorithm (RFC
1323) then each ACK represents an RTT sample.

> Then, my question is: Does tcptrace measure RTT for every ACK?

(I am not the authority, but I believe every ACK is used as an RTT
sample modulo Karn's algorithm.)

allman

--
Mark Allman -- BBN/NASA GRC -- http://roland.grc.nasa.gov/~mallman/
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