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T20P/T26P audio problem on call transfer
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carlos.franco Offline
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Post: #1
T20P/T26P audio problem on call transfer
Hello all!

I'm having a very tricky problem with yealink phones T20P and T26P (almost all my more than 2000 terminals suffer with this problem). The scenario is: phone A calls phone B; Phone B answers the call and transfers it to phone C (no matter if it is an attended or blind transfer). Then the audio from phone A user is completely unperceptive on phone C (choppy and metallic like if there is a problem on RTP synchronism). Audio from phone C to phone A is good.
Additional notes:
1. I tried with and without a SIP proxy. The behavior is the same;
2. Attended transfer is made through pressing * during the call. DTMF are sent to the sip server out of band (RFC 2833);
3. The problem don’t happen if I use G711 codec;
4. When using SIP proxy I tried to capture outgoing RTP packet from the SIP proxy for an entire call. Then I reassembled RTP packet payload for each feed (from proxy to phone A and the other to phone C) onto 2 audio files. Both audio are good, no packet missing and perfectly audible. So the audio exits the proxy in apparently good conditions.
5. I tried several versions of firmware but the behavior is always the same;
6. I googled about the problem and found someone complaining the same but no solution were provided. Someone hinted about problems in the RTP packets timestamp…

If someone have the same problem, is it possible to share his/her findings or maybe point for the solution? I’m pretty sure that it should be something messing with RTP reassembling on the yealink (maybe the timestamp problem I found on google can give an explanation) because I have other phone brands (grandstream and Aastra) that are configured exactly in the same way yealink are and they don’t experience this problem.
Thanks for any clue you can give me.

Regards,
Carlos Franco
05-08-2014 06:52 AM
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T20P/T26P audio problem on call transfer - carlos.franco - 05-08-2014 06:52 AM

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