> I have a question regarding the SDP part of the Invite request. > > suppose user agent "A" wants to talk to user agent "B", he sends a INVITE > request to B. the SDP part of the invite request is as follows, > > > v= 0 > o= A 1464112736 1464112736 IN IP4 151.209.33.190 > s=Calling > c=IN IP4 pgs-477 > t=0 0 > m=audio 2074 RTP/AVP 0 3 5 > a=rtpmap:0 PCMU/8000 > a=rtpmap:3 GSM/4000 > a=rtpmap:5 ADPCM/4000 > > If user agent accepts the request and agrees to talk to user agent A, he > sends a OK response with SDP as followed. > > v= 0 > o= B1464112736 1464112736 IN IP4 151.209.33.194 > s=Answering the call > c=IN IP4 pgs-451 > t=0 0 > m=audio 2074 RTP/AVP 3 5 > a=rtpmap:3 GSM/4000 > a=rtpmap:5 ADPCM/4000 > > now user agent A sends an ACK and starts communication. My question is , > How user agent A is going to know the type of encoding done in the voice > packet recieved from "B"? that is how he is going to come to know whether > it is GSM or ADPCM? >
RTP packet has a payload type (PT) header field. If the payload type is 3 then the payload is GSM encoded else if it is 5 then it is ADPCM encoded. Useragent A should be prepared to receive any of the encodings that is advertised by A to B in INVITE/SDP body. > > _______________________________________________ > Sip-implementors mailing list > [EMAIL PROTECTED] > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors > _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
