Re: tcptrace-bugs Maximum window size using tcptrace questions

From: Wesley Eddy (
Date: 07/12/02

Date: Fri, 12 Jul 2002 16:19:32 -0400
From: Wesley Eddy <>
Subject: Re: tcptrace-bugs Maximum window size using tcptrace questions
Message-ID: <>

On Fri, Jul 12, 2002 at 03:57:06PM -0400, Adam Plesniak wrote:
> Hello, my name is Adam Plesniak and I am a summer intern here at NASA's
> Goddard Space Flight Center. My mentor and I are using your program
> tcptrace to analyze some tcpdump experiments we have been doing. We
> were wondering, how, using the data that your program provides, do you
> determine the set maximum window size of a specific, lets say a single
> file, transmission? Is the maximum set by the receiving computer or the
> sending computer? or possibly the lowest set maximum window of the two?
> Any help on this topic would be great, also, in your program as well as
> the tcpdump program, the optional data mss<****> comes up when an S flag
> is present in a tcp transmission. What exactly does mss mean, and what
> does the number it gives (i.e. 1024) tell us? Any information you could
> provide would be very helpful. My mentor and I really enjoy your
> program and think its great for making tcpdump easier to read. Thanks
> so much for your contribution!

MSS stands for "maximum segment size", RFC 1191 has a nice explanation:

There are a lot of "windows" going on in TCP ... you have a window advertised
by the reciever (the size of its buffer), a congestion window for being
polite to the network, and a transmit window that represents the size of the
buffer for outgoing data. The connection is limited by all of these. The
advertised window appears in packet headers. The others have to be
inferred from the state of the connection and the observed activity.

Also, only list members are allowed to post to the tcptrace mailing list,
as you may have noticed from the webpage, FAQ, or other location where the
list address may be found. There should be signup instructions at all of
those locations.


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