On Tue, 01 Oct 2002, PC Drew <drewpc@xxxxxxxxxxxxxxx> wrote:
> The problem that you're facing is that RTP doesn't define a very
> "unique" way to determine that this UDP data actually is RTP. So, as
> far as I know, the only way you can automagically dissect UDP data as
> RTP is by capturing the control packets as well (i.e. SIP/SDP, IPDC,
> MGCP, RTCP, etc).
Drew,
what you say is correct, and I wrote exactly the same in my email. Now I
start to think my english skills are lower than I thought ;-)
I do get a RTSP packet containing SDP informations, that allow me to map
the RTP payload type to the actual protocol. I actually don't need
automagic dissect, it is enough for me to be able to use "Tools|Decode As"
(obviously automagic would be cool).
I will have a look at your pointers for the code, thanks :-)
Marco
> I haven't worked with RTP in about a year, so I'm a little rusty, but
> as I recall, you can determine the IP:Port information from the
> session control packets (if they're captured as well) in the form of
> SIP/SDP packets for example. I wrote some code a while back to decode
> define the conversation from an SDP packet, but I don't think it ever
> got checked in (as I recall, it had a bunch of memory leaks and
> general "not good code" problems).
>
> Here's my original post:
>
> http://marc.theaimsgroup.com/?l=ethereal-dev&m=99184276504320&w=2
>
> And here was Guy Harris's response. I never took the patch any
> further than my original post because I didn't have time:
>
> http://marc.theaimsgroup.com/?l=ethereal-dev&m=99292667406710&w=2
>
> Hope it helps!
>
> Marco Molteni wrote:
> > Hi,
> >
> > first of all, I would like to say a big THANK YOU to all the people
> > involved in Ethereal :-)
> >
> > The following comes from a MPEG-4 streaming dump but the question is
> > more generic.
> >
> > Real Time Protocol (RTP) has a dynamic range of payload types, from
> > 96 to 127. Ethereal shows (obviously) such RTP packets as payload
> > type=Unknown.
> >
> > One way to know the payload type is from a RTSP/SD packet.
> >
> > Now, let's say I know the payload type, how do I tell ethereal to
> > use that payload type to dissect the RTP packet? Do I just write the
> > dissector and then use "Tools|Decode Packet As" to map the RTP
> > protocol type to my dissector?
> >
> > Also, it seems to me that the "Decode Packet As" doesn't have the
> > granularity that I want, because it allows me to map, for example,
> > UDP plus a source/destination port to a protocol, while what I would
> > like to do is to map the RTP (contained in UDP) type field to a
> > protocol. Any suggestions?
> >
> > thanks for your help
> > Marco
> > _______________________________________________
> > Ethereal-dev mailing list
> > Ethereal-dev@xxxxxxxxxxxx
> > http://www.ethereal.com/mailman/listinfo/ethereal-dev
>
>
>
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