分类：
2009-09-10 22:34:55
From: Shashwat Srivastav ()
Date: 06/24/03
Date: Tue, 24 Jun 2003 05:40:27 -0500
Subject: tcptrace RTT measurement method
From: Shashwat Srivastav <>
Message-Id: <4510B59C-A630-11D7-81B0-000A957C97D2@cs.indiana.edu>
Hello,
I would like to know the exact procedure by which tcptrace collects
data for RTT. Here, I assume that tcptrace gets no additional
information from the raw tcpdump file other than that printed by
tcpdump after parsing the packets (by tcpdump -r raw_file) - correct me
if I am wrong.
In any modern TCP implementation there can be many ways of calculating
RTT from the tcpdump output. If timestamp options is present, tcptrace
can look at the time interval between sending a timestamp and
receiving its echo. It can utilize SACK option to see the time it took
for acknowledgement to reach for each segment sent. Or in the simplest
case, it can keep track of intervals of receiving pure ack. Which
method does tcptrace use ?
Standards mention that rtt should be calculated only when new data is
acknowledged. Does RTT measurement of tcptrace follow this restriction ?
I would be happy to go through the source code if you point me to the
file / function where this is implemented.
Thanks,
- Shashwat
