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Hi,
The screenshot you sent to me showed that
there is packet duplicates in the capture. There is one packet with
sequence number 20744 and then 0.002 seconds later the same sequence number
appears again in the capture for the same RTP stream direction, then there is
0.018 seconds until the next RTP packet with sequence number 20745 and then
0.002 seconds later there is a RTP packet with sequence number 20745 again, and
so on ...
My guess is that the duplicates are the result
of how the port mirrong in the IP switch is working in your case.
Packets between certain ip-addresses may occur twice in the capture in some
cases.
I also think that the code that saves to
au-filemaybe doesn't check the RTP sequence number and/or RTP time stamps in the
way I think that it should do. If there is duplicates it should not
save the duplicate in the au-file, I think (but the rtpdump file should
contain all the rtp packets in the order they arrive).
I haven't checked the code in detail yet and
I didn't find any sample capture with duplicate G.711 packets that I could
try with. I haven't experimented so much with the
RTP Analysis lately, but will do that soon anyway.
The save to au-file code seems to add silence if
there is silence suppresion, but I'm not sure exactly how it handles out of
sequence packets, duplicated packets and dropped packets when storing to an
au-file.
An alternative you could try is
to save the file in rtpdump format and use rtpplay. The rtpplay
program will send packets either according to the RTP stamp or the "arrival
timestamp" timestamp (-T option), and JMF JMPlayer program will
probably look at the RTP sequence number and/or RTP timestamp for the
received packets, and not
use the duplicate packets. I guess that JMPlayer is
handling out-of-sequence packets etc. but I'm not sure about it.
I think that I got good results when using some
rtpdump files with duplicate packets (every packet appearing twice) a while
ago when replaying the rtpdump file towards JMPlayer.
Regards,
Martin
----- Original Message -----
Sent: Friday, November 14, 2003 7:36
AM
Subject: [Ethereal-users] URGENT: Need
help with RTP stream playback issue
Hello folks,
I am doing some lab tests on my IP phone calls using Ettercap 0.9.a
and Ettercap 0.9.16.
Specific Problem:
I can mark the RTP packets in Ethereal and save the voice stream as
.au file (8000 Hz, 8 bit, mono, both Channels).
However when I play this audio file using Windows Media Player, the
playback is VERY slow and robotic.
Is this a common problem? How do I fix it? I have the same results
when I try to use Real Player.
My deadline is very close, so any help would be greatly
appreciated.
Thank you!
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