Ethereal-users: RE: [Ethereal-users] Problems saving RTP payload (G.711 PCMU)

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From: "Oliveras, Michael" <mike.oliveras@xxxxxxxxxxxxx>
Date: Tue, 14 Dec 2004 11:10:04 -0500
I have had similay issues if for example rfc2833 is used for DTMF relay.
The RTP payload type for RTP packets using rfc2833 is usually 101, which
will be different for the payload type for the codec used in the call (g729,
g723, etc..)

If that is the case, maybe you can save all RTP packets except those and try
it again?

- Mike


-----Original Message-----
From: Andrew Becherer [mailto:shadygrove@xxxxxxxxx]
Sent: Tuesday, December 14, 2004 12:10 AM
To: ethereal-users@xxxxxxxxxxxx
Subject: [Ethereal-users] Problems saving RTP payload (G.711 PCMU)


Hello all,

I am using ethereal to explore my Vonage VOIP service. I am using
etheral 0.10.7 built on Mac OS 10.3.6 using fink. I have a Cisco
ATA-186 analog telephone adapter and I am interested in its traffic.
As I am on a switched network I have been doing the capturing on the
my gateway(a PII box with smoothwall). I am limited to using tcpdump
for the capture, no big deal. From the ethereal docs I found out about
tcpdump (tcpdump -w <file-name> -s 1500 host <ip of cisco ata186>).

Now the trouble; I have been getting very spotty results on saving the
payload of the RTP streams in the .au audio format. I have tried 5
captures so far, and only 1 has been a complete success. In 4 of the
cases either the "forward direction" or the "reversed direction" will
not decode. Ethereal will return an error "Can't save reversed/forward
direction in a file: Unsupported codec!" I know this codec is
supported (G.711 PCMU). In each case I could save the payload of
either the forward or reversed stream but not both

Can anyone offer some advice for increasing the probability I will be
able to save the payload of both the forward and reversed stream?

I realize this feature has not been in ethereal too long(March of 2003
according to the developers list). I have done quite a bit of
googling/searching the mailing lists, I have tried using
vomit(different trouble there), and I just started trying rtptools and
the java media framework. I would prefer to just use ethereal. On the
one RTP stream it did a fantastic job.

-- 
Andrew B

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