Ethereal-users: Re: [Ethereal-users] RTP Analysis: Error: "Can't save in a file:Unsupported code
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Cool idea, but what this amounts to is almost equivalent to
implementing a proper RTP layer within Ethereal. To "insert silence"
means analyzing the special event (DTMF), and *generating* the
silence. This is not trivial nor should this functionality be provided
by a utility like Ethereal.
I'm not an Ethereal expert and there may be a way to get this to work,
but it seems like we're stretching the definition of a packet sniffer a
bit. The thing is that RTP can be quite complex - it's rarely a simple
bitstream that can be assembled into a .wav file.
Still, Ethereal continues to amaze me so I don't want to dampen
enthusiasm. :)
Maybe a better idea would be to create a small app that combines
libpcap and GNU ccrtp...?
Erik Naslund wrote:
That's right. You shouldnt remove anything from the stream when you're
interested in reconstructing it later (rtpdump/rtpplay).
However, the "save payload" functionality should be modified in order to
ignore anything that's not voice (voice=only G.711 for the moment) and that
shouldn't disturb the audio content too much, does it?
I think that's what he's talking about. I had no time to look at the capture
file for the moment however.
The audio content gets disturbed when you remove the DTMF packets. The
more packets of this type, the more the timing of the conversation is
off. Think about calling your credit card company, when you enter in
your full CC #, plus following the menu prompts. This could cause the
timing of the conversation to be off by several seconds.
Again, if the Save Payload functionality could simply insert silence
or false tones during the audio encoding process, this would preserve
the timing of the conversation.
IANAD but it would seem doable, as the DTMF packets seem very detailed
as to how long the button is pressed, which button it is, and when it
"ends".
I am a very grateful user of a fabulous FOSS package. I dont want to
come off as disgruntled or ignorant. Thanks for all the work everyone
does on making ethereal such an awesome tool for sysadmins such as
myself, as well as the casual home user. You guys are great.
-Erik
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