tcptrace How to get the RTT _actually_ sampled by TCP?

From: Liangping Ma (lma@mail.eecis.udel.edu)
Date: 08/17/04 

Date: Tue, 17 Aug 2004 11:51:23 -0400 (EDT)
From: Liangping Ma <lma@mail.eecis.udel.edu>
Subject: tcptrace How to get the RTT _actually_ sampled by TCP?
Message-ID: <Pine.GSO.4.58.0408171124270.14743@frink.ece.udel.edu>

Hello,

I measured the RTTs for a TCP connection using tcptrace. I found that the
number of RTTs is almost equal to (in fact, a little bit less than) the
number of packets sent. For example, in one TCP session,

pure pkts sent: 7857
sack pkts sent: 150

The number of RTTs obtained by TCP is 7614. So tcptrace samples round-trip
time almost once per packet.

BUT, TCP only samples the round-trip time once per RTT (rather than once
per packet). [see p. 468 Computer Networks, L. Peterson and B. Davie, 2nd
Ed., 2000].

How do you get the RTTs that are _actually_ sampled by TCP?

Thanks.

Liangping

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