tcptrace Patch for Cwnd and RTT estimation at a receiver

From: Wolfgang Hansmann (hansmann@cs.uni-bonn.de)
Date: 06/03/03 

Message-ID: <3EDCEB28.1090707@cs.uni-bonn.de>
Date: Tue, 03 Jun 2003 20:38:32 +0200
From: Wolfgang Hansmann <hansmann@cs.uni-bonn.de>
Subject: tcptrace Patch for Cwnd and RTT estimation at a receiver

Hi,

The current tcptrace version 6.4.2 is able to generate OWIN and RTT
plots. For useful results the tcpdump trace must be taken close to the
sender of a TCP connection, but this is not always posssible.

I'd like to contribute a patch to solve this problem. It is available at

http://http://web.informatik.uni-bonn.de/IV/Mitarbeiter/hansmann/tcptrace/tcptrace-6.4.2_rcwnd.patch

The patch enables congestion window (or more precise: \min(cwnd,
rwin)) and rtt graphs based on a tcpdump trace taken at the receiver's
end of a connection. It requires both peers to use the TCP timestamp
option during the connection and uses them to match an incoming data
segment to a previously transmitted ACK. The estimated congestion
window corresponds to the difference between the segment's and the ack's
sequence number.

This method collects RTT and CWND samples based on the granularity of
the receiver's TCP timestamp information.

The patch enables two new options:

-H

    Plot the remote end's \min(cwnd, rwin) over time as estimated by
    the receiver. The plot is written to *_rcwnd.xpl. An example plot
    is available at
 
http://web.informatik.uni-bonn.de/IV/Mitarbeiter/hansmann/tcptrace/rcwnd.png

-I

    Plot RTT samples over time. The plot is written to *_rrtt.xpl. An
    example plot is available at
 
http://web.informatik.uni-bonn.de/IV/Mitarbeiter/hansmann/tcptrace/rrtt.png

Both plots are generated from tcpdump output recorded on 03/05/22, at
my (receiving) machine while wgetting
http://www.ietf.org/iesg/1rfc_index.txt. (I was surprised to see the
IETF web server still being attached to the Internet via a plain T1
link. The RRT graph shows nicely how the link's transmission queue
piles up as the cwnd grows)

Wolfgang Hansmann

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