5 jan 2010 kl. 10.08 skrev hadi motamedi: > > > On Tue, Jan 5, 2010 at 8:59 AM, Olle E. Johansson <[email protected]> wrote: > > 4 jan 2010 kl. 14.46 skrev Kevin P. Fleming: > > > 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. > > But it's fairly common to have asymmetric media in the call. If the caller > offers A, B and C and the callee responds with B, the caller sends B but the > callee might send A. > > /O > > > > Sorry . You mean we can have asymmetric codecs in Asterisk ? > As Kevin stated, for Asterisk, the server switches to the format we receive, so no. I just pointed out that it happens quite often that a call is asymmetric, and you will see Asterisk trying to follow the other side.
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