Hi Jeff,
I have to analyze a lot of trace files and found the graphical
stuff very helpful to find the interesting places in the trace file.
Have you tried it? If you miss a feature there, Irene can implement
it...
if it does not take too much time.
Best regards
Michael
On May 10, 2006, at 12:09 PM, Jeff Morriss wrote:
[Resending since my first attempt died a horrible SMTP-server-not-
relaying-for-ethereal.com death.]
Hi Michael,
I guess that's true that this goes hand-in-hand with reassembly. :-)
In terms of finding all the packets, I've usually had 2 cases: 1)
where
I'm seeing retransmissions in a single capture file and 2) where I've
got 2 capture files that might have retransmissions. For (2) I
usually
use 'mergecap' to make one file and go from there. But (1) usually
trips me up more because, when looking at/for higher layer problems, I
tend to skip details like verifying the peer is actually sacking us
in a
timely manner--so a color filter would be useful to bring the
retransmissions to my attention.
Regards,
-Jeff
Michael Tuexen wrote:
Hi Jeff,
one of the problems is that you need all packets on the trace.
Since SCTP
supports multihoming, this might be more difficult to achieve.
It is also harder to find associations... The graphical analysis tool
does this based on two facts:
1. If it has the INIT and INIT-ACK in the trace, it analyses them and
uses the IP-addresses (multiple), port numbers and V-Tags.
2. If not all addresses are available (for example, the INIT or
INIT-ACK has not been seen, it uses the port numbers and V-Tags
only. The critical point here is that you do not have all
information
in one packet (like in the TCP case) except for the INIT-ACK.
If you want to see how this works, have a look at the code the the
SCTP association analysis tool. It provides really nice graphics
which
we use to find retransmissions and so on. You can also filter for
associations.
For the experience we made, the above method 2 is very good.
A student of mine is going to implement reassembly for SCTP DATA
chunks and
also therefore also needs some way of finding associations, the
first step
will be to integrate SCTP in the conversation concept...
After that in place, doing a sequence number analysis and having a
tracefile
covering all paths should be as hard as for TCP. So it is on the
agenda, but
the problem is the time. In the meantime, have a look at the GUI
tool. It
really helped us to find a lot of bugs...
Best regards
Michael
On May 4, 2006, at 9:32 AM, Jeff Morriss wrote:
So if I were to ever actually find the time to study the TCP
sequence analysis code (which detects retransmissions, associates
acks with the acked data, etc.) in the hopes of doing something
similar in SCTP, is there anything I should know about the TCP
code? Any known deficiencies or things that could be done better?
(Of course I'm probably kidding myself that I'll ever find the
time, but I keep getting confused by retransmissions that I
didn't notice were retransmissions the first N times I looked at
them.)
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