[SIPForum-discussion] Regarding RTP audio packets getting dropped by the media gateway with SIP calls.

[Aniella Juverdeanu]

The RTP path and parameters are negotiated in SDP of the Invite and the SDP response in 183, if present, and/or 200 OK - when you check the trace on the 192.168.1.76 side.

Most likely the proxy is just for signaling (pretty normal in VoIP networks) - therefore if 192.168.1.76 is in the SDP of the Invite in C= line then this IP address has to route RTP packets to media connection endpoint is 195.186.130.132.

Regards,
Aniella

From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of Badri Ranganathan
Sent: April 23, 2014 01:22 AM
To: discussion at sipforum.org
Subject: [SIPForum-discussion] Regarding RTP audio packets getting dropped by the media gateway with SIP calls.

Hi all,

I have 2 SIP endpoints (192.168.1.76 making the call and 192.168.1.72 answering the call).  The call is made via a proxy server in between which is 195.186.130.4.
Then 192.168.1.76 plays out audio RTP and 192.168.1.72 is supposed to record this audio. That is the test.

I am facing a strange problem with RTP audio not being received by 1.72 although it is being played out from 1.76

The calls are established through SIP without any problem. The SDP exchange also seems to be fine with both ends exchanging PCMU (Owner in SDP is 195.186.130.4 and media connection endpoint is 195.186.130.132 (presume it is some media gateway assigned by the proxy))

The endpoint 192.168.1.76 has played out audio RTP but the receiver has not received anything. (AC_rec.txt will confirm that)
However I am able to see that the RTCP exchange between these endpoints through the media gateway is fine without any issue.

I cannot view or debug at the media gateway since I have no authority to do it. But my reason to believe that the RTP must have reached the media gateway and that it is the media gateway dropping it  - The RTCP packets are getting across without a problem !!! Therefore the RTP packets must have definitely reached the MG and the MG is dropping it because it doesn't like them for some reason :(

Why does the media gateway not forward the RTP packets that 192.168.1.76 has sent?
Any way of debugging through the RTCP protocol itself?
Is there any issue in the SDP negotiation between the SIP endpoints or with the RTP packets itself?

Will be very helpful if someone can please look at the wireshark traces attached with this email.  Any help in this regard is very much appreciated.

Thanks,
Badri.


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