Ethereal-dev: [Ethereal-dev] RE: [Ethereal-users] Forcing ISDN Q931 trace..

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From: Biot Olivier <Olivier.Biot@xxxxxxxxxxx>
Date: Mon, 17 May 2004 16:10:31 +0200
|From: Steve Matthews
|
|
|Hi
|I tried to enable the ability to decode Q931 on top of UDP 
|port 9011.  I was unable to force the decode as its does
|not appear in the list.. using 0.10.4 release

The Q.931 dissector has not been coded in a way that it can run *directly*
on top of UDP. You can do so however if you're familiar with compiling
Ethereal, you then have to add the following line somewhere in the handoff
routine "proto_reg_handoff_q931()" for Q.931:

	dissector_add("udp.port", 9011, q931_handle);

If this port is not a fixed port, then you may want to add a preference for
the port.

|I also tried to see if I could then force an offset of X
|bytes and tell it to decode..
|Don't see a way to do this which you can do with Sniffer..

This is not possible today. It could however be implemented by means of a
generic "skip" dissector for which we need only to provide the number of
bytes to skip. Note to the developers: we should have the possibility to
specify a per-conversation byte offset and protocol handoff.

|Am I doing something wrong or is the above not possible.

If the Q.931 protocol really runs directly over UDP, then the code has to be
updated.

Otherwise (if it runs on top of another protocol) you must specify the name
of the protocol running immediately on top of UDP. That one will then
normally take care of handing off the data to the correct higher-layer
protocol dissectors (and eventually Q.931).

Regards,

Olivier