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<p class="MsoNormal" style="background:white"><span style="color:#212121">Hi,<o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="color:#212121"><o:p> </o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="color:#212121">We have a scenario where inbound calls from an upstream provider (chan_sip) sent downstream (chan_iax2) negotiates only g729
</span><span style="color:black">yet</span><span style="color:#212121"> RTP media contains g711</span><span style="color:black">.
</span><span style="color:#212121">Both the upstream and downstream trunks are limited to only offering g729 whilst the initial invite from our upstream provider offers both g711 and g729. Asterisk presumably simply forwards the media from iax2 trunk encapsulation
to sip encapsulation. Most calls surprisingly work, presumably by the caller's system identifying the incoming media as g711</span><span style="color:black">,</span><span style="color:#212121"> whilst very few callers don't hear the IVR prompt.</span><span style="color:black">
</span><span style="color:#212121">The downstream is unfortunately not within our control but can't be anything other than Asterisk, considering it's using iax2 in trunk mode.<o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><o:p> </o:p></p>
<p class="MsoNormal" style="background:white"><span style="color:black">We are running Asterisk 16.13.0, not sure what version the downstream is using.</span><o:p></o:p></p>
<p class="MsoNormal" style="background:white"><o:p> </o:p></p>
<p class="MsoNormal" style="background:white"><span style="color:#212121">caller -> upstream -> us -> downstream (IVR)<o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><o:p> </o:p></p>
<p class="MsoNormal" style="background:white"><span style="color:black">Herewith the SIP portion of the call, between upstream and us:</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt;background:white"><span style="color:black">Available here: https://ibb.co/jRGvvVc</span><o:p></o:p></p>
<p class="MsoNormal" style="background:white"><span style="color:#212121"><o:p> </o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="color:#212121"><o:p> </o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="color:#212121">Wireshark unfortunately still cannot dissect iax2 trunk captures though, so I didn't know how to conclusively
</span><span style="color:black">identify where this problem </span><span style="color:#212121">originates.</span><span style="color:black"> I do however have a concern that the media we are receiving’s packet size (74 bytes) indicates that it is most likely
G729.</span><span style="color:#212121"><o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Herewith the IAX2 trunk portion of the call, between us and downstream:<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt">Available here: https://ibb.co/r07PkkK<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">ie: We appear to have a reproducible environment where an inbound SIP trunk call sent to a downstream IAX2 trunk negotiates g729 in all 4 streams, receives g729 media from downstream iax2 trunk but then transmits g711a upstream.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m however struggling with the downstream pcap, to establish what’s different about these calls. Trunk config and forwarding structure works the identical way for 50+ other flows on the same host.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Regards<br>
David Herselman<o:p></o:p></p>
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