Wireshark-dev: Re: [Wireshark-dev] how do you get SDP dissector info to use it with a new disse
From: "Luis EG Ontanon" <[email protected]>
Date: Tue, 22 Apr 2008 15:24:31 +0200
I do not understand what you want to do.

If all you want is to get RTP's media dissected just invoking the sdp
dissector to dissect the sdp buffer might be enough. SDP will take
care of "registering" the RTP converstations definded in it so that
related media packets are passed to RTP and that RTP calls the propper
dissector for the payload.

You can take a look on how packet-rtsp.c or packet-sip.c hand over to
sdp and how amr or iuup register themselves to be usable as dynamic
RTP payload.

Hope this helps


On Tue, Apr 22, 2008 at 3:11 PM,  <[email protected]> wrote:
>
>
> Hi everyone,
>
> I've been working on a new dissector that I'll hopefully be able to
> contribute.
>
> So far I've used the protocol preferences menu to allow me to "setup"
> parameters that are usually found in an SDP file or via SDP/SAP or via
> SDP/RTSP.
>
> This can be quite tedious as I'm switching between different RTP streams,
> each having potentially different setup parameters.
>
> Hence I would like to try and reuse the already dissected SDP parameters (if
> found) and use those automatically i.e.
>
> If  SDP -> Media Format (sdp.media.format)  = certain value,
>
> then
>     Search    SDP -> Media format specific parameters (sdp.fmtp.parameter)
>             If found "setup" parameter, "store" the value for that setup
> parameter and associate it with the associated sdp.media.format type
>     End search
> End SDP search
>
> As I expect the SDP information to contain declarations for multiple RTP
> streams with different dynamic payload types, each having setup parameters
> for my dissector, what is the best approach I can take?
>
> How do I search for any relevant SDP info?
>
> I've tried to find relevant examples but haven't exactly succeeded and would
> appreciate a pointer. Wireshark seems extremely powerful but it's rather
> daunting to a beginner.
> I came across tapping, but I'm not sure whether I need to get info from the
> SDP tap, or whether I need to create a tap for my dissector....or even tap
> at all?!
>
> As for using those parameters:
>
> Should I define a structure containing all the relevant setup parameters,
> define a table containing pointers to that structure, and populate it
> accordingly for each relevant stream i.e. RTP payload type in SDP having my
> setup parameters?
>
> The idea would then be to search this table for a matching RTP payload type
> so that my dissector can use the correct setup parameters, extracted
> automatically from SDP, rather than using the potentially incorrect setup
> parameters defined in my preferences.
>
> Thanks for your help,
>
> David
>
>
>
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