hadi motamedi wrote: > Sorry . I didn't get the point clearly . In the SIP Invite message , it > says "my audio endpoint is IP x.x.x.x port x, and I can use codecs > A,B,C". The remote endpoint responds with a 200 OK, saying "my audio > stream is at IP y.y.y.y port y, and I choose codec B". Can you please do > me favor and let me know if my understanding is right or not ? > Thank you
No, you are not understanding the SDP offer/answer model properly. If one endpoint offers codecs A, B and C in its SDP, it is willing to *receive* media in those formats. The receiver of that offer can choose to send media to the offerer in any of those formats, at any time. If the answering endpoint includes only codec B in its SDP, then it is willing to *receive* only codec B. In that scenario, it is possible for media to flow from endpoint 1 to endpoint 2 using codec B, and from endpoint 2 to endpoint 1 using codec A (or C), but this will not happen if Asterisk is an endpoint in this scenario. When Asterisk receives a media frame, if the format of that frame is not the format that it is currently sending to the other endpoint, it will switch to that format automatically. If it cannot do so because the other endpoint did not offer to receive that format, then the call's audio will probably fail. This is the reason why I responded before that Asterisk does not support asymmetric formats in a media session. In reality, it is extremely uncommon for a SIP endpoint to want to send media in a format that it is not also willing to receive; in fact, I can't say I've ever seen this situation arise in any testing I've done or in any issues reported in our issue tracker. -- Kevin P. Fleming Digium, Inc. | Director of Software Technologies 445 Jan Davis Drive NW - Huntsville, AL 35806 - USA skype: kpfleming | jabber: kpflem...@digium.com Check us out at www.digium.com & www.asterisk.org _______________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users