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<p class="MsoNormal">I am trying to set-up an Asterisk server to ”transcode” between different RTP frame sizes. I have devices on one side using alaw with ptime 20 ms and some equipment on the other side requiring ptime 10. I am using the latest Asterisk 13.8.0.
The set-up looks like this:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> A (ptime 20) ---> asterisk ---> B (ptime 10)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">In Asterisk I have two peers defined with only one codec in each, alaw:10 and alaw:20 respectively. The SIP call set-up looks fine and each side announces the correct ptime in the SDP (both Asterisk and B has the ptime=10 attribute in the
SDP). The dialplan is currently first answering A’s call, plays a prompt and then Dial() into B.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This is what the media streams look like, including RTP frame size:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> A --- 20ms -------> asterisk -----20ms!-----> B<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"> A <-- 20ms ------- asterisk <-----10ms---- B<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The stream from Asterisk to B has the wrong frame size, it should be 10ms. Looking at the media from B to A, we can see that asterisk properly changes frame size in one direction.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I also tried to use ulaw on the path between Asterisk and B to see if that would trigger a proper transcoding, but the results were the same (in terms of frame size, but with correct change of codec ).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Is this supposed to work? Any suggestions for workarounds?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Best regards,<o:p></o:p></p>
<p class="MsoNormal">Jan Blom<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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