Ethereal-users: Re: [Ethereal-users] URGENT: Need help with RTP stream playback issue
Hello Martin and everyone,
Thanks for all the prompt help and assistance so far! I installed RTPplay and JMF and it works with those tools! I also feel that the duplicate packet sequences may have something to do with my problem.
Question: Is it possible to save both forward and reverse streams within the same file for RTPplay?
For the benefit of the group, here are the specific steps I used to get it to work:
1) Within Ethereal, I marked the packets as RTP. Then I saved the forward and reverse streams individually( Tools --> Statistics --> RTP Streams--> Show All.
2) Launched JMF Studio (Programs ---> JMF 2.1.1e --> JMF).
3) Within Studio, I clicked on File --> Open RTP session. Specified MyPCaddress and port# (example: 1.1.1.1 and port 2000)
4) On my DOS prompt, I typed
rtpplay.exe -f <RTPdumpfilesavedinstep1> <MyPCaddress>/Port# for JMF to listen on
Example:
rtpplay.exe -f file1 1.1.1.1/2000
5) This should automatically launch another window to play the audio.
I also feel that the duplicate packet sequences may have had something to do with my problem.
To clarify, I am not mirroring the switchport. My laptop is in the same VLAN as my IP phones in the lab and I used the ARP based sniffing option (-a) within Ettercap to capture the RTP stream . Is the duplicate packet problem common with Ettercap's ARP sniffing feature?
Thanks again!
Martin Regner <martin.regner@xxxxxxxxx> wrote:
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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