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<p>Hello Ryan,</p>
<p>the replies are forwared with the Via header. So if there is no second Via header in the reply from the MRCP server, Kamailio can't properly route this. So this looks like an issue with the MRCP.</p>
<p>Have a look to this example for a somewhat similar setup that describe it in detail:
<a class="moz-txt-link-freetext" href="https://tools.ietf.org/html/rfc3665#section-3.2">
https://tools.ietf.org/html/rfc3665#section-3.2</a></p>
<p>Cheers,</p>
<p>Henning<br>
</p>
<div class="moz-cite-prefix">Am 23.08.19 um 23:25 schrieb Ryan McEvoy:<br>
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<p class="MsoNormal"><span style="font-size:11.0pt">Hello,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">I have been having an issue using kamailio to load balance to a SIP/MRCP server. I believe that the issue actually lies with the reply being sent from the final recipient, but I wanted to be sure that I understood
the problem and to see if there were any possible solutions within Kamailio.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">I am using the dispatcher module to dispatch SIP INVITES to media resources, in this case I am just using a single host in a single dispatcher group. The configuration that I have has worked just fine for
other SIP/MRCP servers, which is why I think the issue is with this target in particular.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">The INVITE is routed correctly and contains the headers that it should. The invite comes originally from a Freeswitch, arrives at Kamailio, who should then dispatch to a host in the group.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">x.x.x.x:4901 is Kamailio<br>
x.x.x.x:8090 is Freeswitch<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">y.y.y.y:8000 is the final target<br>
<br>
This is the invite, as received by the final target after dispatched via Kamailio<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">INVITE sip: x.x.x.x:4901 SIP/2.0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Record-Route: <sip: x.x.x.x:4901;transport=tcp;lr><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Via: SIP/2.0/TCP x.x.x.x:4901;branch=z9hG4bK3a9a.7f9a4b588cd75108cfea9a2bd9ffa829.0;i=3<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Via: SIP/2.0/TCP x.x.x.x:8090;branch=z9hG4bKStXp06Sv7jU7S<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Max-Forwards: 69<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">From: <sip: x.x.x.x:8090>;tag=4gHgNcNUDjvFQ<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">To: <sip: x.x.x.x:4901><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Call-ID: 6f2a0e9c-3f9e-1238-2aa9-005056854777<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">CSeq: 8692231 INVITE<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">User-Agent: tts<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, PRACK, MESSAGE, SUBSCRIBE, NOTIFY, REFER, UPDATE<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Supported: timer, 100rel<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Content-Type: application/sdp<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Content-Disposition: session<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Content-Length: 281<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">v=0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">o=IPSoft 3367790083977298880 2789991278648035021 IN IP4 x.x.x.x<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">s=-<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">c=IN IP4 x.x.x.x<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">t=0 0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">m=application 9 TCP/MRCPv2 1<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=setup:active<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=connection:existing<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=<a class="moz-txt-link-freetext" href="resource:speechsynth">resource:speechsynth</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=cmid:1<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">m=audio 32038 RTP/AVP 0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=rtpmap:0 PCMU/8000<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=recvonly<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=mid:1<br>
<br>
The reply that the server sends back appears to be missing a second Via header, which is preventing Kamailio for routing it correctly (based on the error message from core/forward.c)<br>
<br>
This is the reply sent by the target destination<br>
<br>
SIP/2.0 200 OK<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Via: SIP/2.0/TCP x.x.x.x:8090;branch=z9hG4bKStXp06Sv7jU7S<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">To: <sip: x.x.x.x:4901>;tag=ndszib3k<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">From: <sip: x.x.x.x:8090>;tag=4gHgNcNUDjvFQ<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Call-ID: 6f2a0e9c-3f9e-1238-2aa9-005056854777<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">CSeq: 8692231 INVITE<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Contact: "Voiceware MRCP Server"
<a class="moz-txt-link-rfc2396E" href="mailto:sip:vwmrcp@y.y.y.y:8000;transport=tcp">
<sip:vwmrcp@ y.y.y.y:8000;transport=tcp></a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Content-Type: application/sdp<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Content-Length: 324<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">v=0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">o=- 1566492047 1566492047 IN IP4 y.y.y.y<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">s=Voiceware MRCP Server 2.15.0.7. Dec 28 2018<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">c=IN IP4 y.y.y.y<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">t=0 0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">m=application 8002 TCP/MRCPv2 1<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=channel:12951125463@speechsynth<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=connection:new<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=setup:passive<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=cmid:1<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">m=audio 30158 RTP/AVP 0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=rtpmap:0 pcmu/8000<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=sendonly<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=ptime:20<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">a=mid:1<br>
<br>
It is correct that there should still be a 2<sup>nd</sup> Via header in the 200 OK reply from the target host, right?<br>
<br>
If so, is there anything else that can be done in Kamailio to handle this, or is this mrcp server simply not complying properly with SIP?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">There’s no funky natting between these hosts or anything like that.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Thanks in advance!<o:p></o:p></span></p>
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<pre class="moz-quote-pre" wrap="">_______________________________________________
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<pre class="moz-signature" cols="72">--
Henning Westerholt - <a class="moz-txt-link-freetext" href="https://skalatan.de/blog/">https://skalatan.de/blog/</a>
Kamailio services - <a class="moz-txt-link-freetext" href="https://skalatan.de/services">https://skalatan.de/services</a></pre>
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