Hi, I think I found a problem with the SDP offer-answer implementation recently merged into master while implementing wideband functionality. The problem is with the assignement of dynamic payload types. SEMS seems to keep only one mapping of dynamic payload types to codec implementation, which is global to all of SEMS. However, it should keep two separate mappings - one for sending and one for receiving - for each RTP stream. This problem shows in the following setup:
I use twinkle to setup a call to SEMS, which plays an announcement using the speex wideband codec. Twinkle sends the following SDP in the INVITE: v=0. o=twinkle 1229564934 1632772146 IN IP4 192.168.1.121. s=-. c=IN IP4 XX.XX.XX.XX. t=0 0. m=audio 13006 RTP/AVP 98 97 8 0 102 3 101. a=rtpmap:98 speex/16000. a=rtpmap:97 speex/8000. a=rtpmap:8 PCMA/8000. a=rtpmap:0 PCMU/8000. a=rtpmap:102 G726-16/8000. a=rtpmap:3 GSM/8000. a=rtpmap:101 telephone-event/8000. a=fmtp:101 0-15. a=ptime:20. a=nortpproxy:yes. This means, that twinkle expects the speex wideband codec under payload type 98 and the speex narrowband codec under payload type 97. SEMS answers with the following SDP in the 200 OK: v=0. o=sems 1 1 IN IP4 XX.XX.XX.XX. s=sems. c=IN IP4 89.246.236.49. t=0 0. m=audio 10000 RTP/AVP 97 96 8 0 101. a=rtpmap:97 speex/16000. a=rtpmap:96 speex/8000. a=rtpmap:8 PCMA/8000. a=rtpmap:0 PCMU/8000. a=rtpmap:101 telephone-event/8000. This means, that SEMS expects the speex wideband codec under payload type 97 and the speex narrowband codec under payload type 96. Unfortunately, SEMS sends speex wideband encoded RTP packets with payload type 97. This leads to twinkle decoding the audio with the narrowband decoder and to poor audio quality. As mentioned above, to fix the problem, SEMS has to keep a seperate payload type mapping for sending and it has to set the payload type on outgoing packets according to this mapping. Since we need this functionality at ISACO quite urgently, I would be willing to implement a fix for this. What do you think? Regards, Emil -- Emil Kroymann VoIP Services Engineer Email: [email protected] Tel: +49-30-203899885 Mobile: +49-176-38389303 ISACO GmbH Kurfürstenstraße 79 10787 Berlin Germany Amtsgericht Charlottenburg, HRB 112464B Geschäftsführer: Daniel Frommherz
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