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<div class="gmail_quote">On Tue, Jan 5, 2010 at 8:59 AM, Olle E. Johansson <span dir="ltr"><<a href="mailto:oej@edvina.net">oej@edvina.net</a>></span> wrote:<br>
<blockquote style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" class="gmail_quote"><br>4 jan 2010 kl. 14.46 skrev Kevin P. Fleming:<br>
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<div class="h5"><br>> hadi motamedi wrote:<br>><br>>> Sorry . I didn't get the point clearly . In the SIP Invite message , it<br>>> says "my audio endpoint is IP x.x.x.x port x, and I can use codecs<br>
>> A,B,C". The remote endpoint responds with a 200 OK, saying "my audio<br>>> stream is at IP y.y.y.y port y, and I choose codec B". Can you please do<br>>> me favor and let me know if my understanding is right or not ?<br>
>> Thank you<br>><br>> No, you are not understanding the SDP offer/answer model properly. If<br>> one endpoint offers codecs A, B and C in its SDP, it is willing to<br>> *receive* media in those formats. The receiver of that offer can choose<br>
> to send media to the offerer in any of those formats, at any time. If<br>> the answering endpoint includes only codec B in its SDP, then it is<br>> willing to *receive* only codec B. In that scenario, it is possible for<br>
> media to flow from endpoint 1 to endpoint 2 using codec B, and from<br>> endpoint 2 to endpoint 1 using codec A (or C), but this will not happen<br>> if Asterisk is an endpoint in this scenario.<br>><br>> When Asterisk receives a media frame, if the format of that frame is not<br>
> the format that it is currently sending to the other endpoint, it will<br>> switch to that format automatically. If it cannot do so because the<br>> other endpoint did not offer to receive that format, then the call's<br>
> audio will probably fail. This is the reason why I responded before that<br>> Asterisk does not support asymmetric formats in a media session.<br>><br>> In reality, it is extremely uncommon for a SIP endpoint to want to send<br>
> media in a format that it is not also willing to receive; in fact, I<br>> can't say I've ever seen this situation arise in any testing I've done<br>> or in any issues reported in our issue tracker.<br>
<br></div></div>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.<br><font color="#888888"><br>
/O<br></font>
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<div>Sorry . You mean we can have asymmetric codecs in Asterisk ?</div>
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