Robert Watson wrote:
On Thu, 1 Dec 2005, Vlad GALU wrote:
On 12/1/05, Alin-Adrian Anton <[EMAIL PROTECTED]> wrote:
Dear Hackers,
I would like to monitor the changes of cwnd and sstresh
values during
TCP traffic, in order to plot graphs and interpret congestion.
So I need (cwnd, timestamp) and (sstresh, timestamp) records
to be
taken everytime one of the two variables is modified.
I'd like to ask you for suggestions, which would be the best
aproach
(kernel patch, kernel module, etc?), and how would this be done best?
(the interception of values, the storage of snapshots, etc)?
Does exporting them via sysctl, and graph them using anything
(rrdtool) sound reasonable ?
I thought about this too, however, this loses precision and provides
constant units of time. Knowing the timestamps for each packet may be
interesting to underline timeouts on the graphic.
I've not used it, but there is a TCPDEBUG kernel option that gathers TCP
state information for debugging and tracing purposes. I know this has
been used quite effectively in the past for this sort of work, but
unfortunately I know very little about it. With all the TCP changes in
the last few years (SACK, etc), it could be that it needs some
enhancements, cleanups, fixes, etc.
I used it now, and with a small patch it shows exactly what I need (seq,
ack, timestamp, cwnd and ssthresh). I just added my knob to trpt.c .
I also modified the iptime() function to provide microsecond resolution
instead of miliseconds, because most of the packets have the same
timestamp attached. Still, a decent number of packets have the same
timestamp. I'm looking at them only on one side of the connection (the
transmitter), I wonder if there is any better solution then timestamping
them on both sides - and mixing the values.
Thanks guys for the precious information, it helped a lot!
Yours Sincerely,
--
Alin-Adrian Anton
GPG keyID 0x183087BA (B129 E8F4 7B34 15A9 0785 2F7C 5823 ABA0 1830 87BA)
gpg --keyserver pgp.mit.edu --recv-keys 0x183087BA
"It is dangerous to be right when the government is wrong." - Voltaire
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