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<p class="MsoNormal">I’m pretty sure the RFCs state that a CANCEL should only be sent if some response, usually 100 Trying, has been received. This is to avoid the possibility of the INVITE and CANCEL being received out of order at the destination.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:black">Ben Newlin </span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">Users <users-bounces@lists.opensips.org> on behalf of John Quick <john.quick@smartvox.co.uk><br>
<b>Date: </b>Wednesday, June 30, 2021 at 11:19 AM<br>
<b>To: </b>users@lists.opensips.org <users@lists.opensips.org><br>
<b>Cc: </b>solarman@one-n.co.uk <solarman@one-n.co.uk><br>
<b>Subject: </b>Re: [OpenSIPS-Users] fr_timeout CANCEL message sent to timed out dispatcher endpoint IP<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">That sounds like reasonable behaviour to me, at least for UDP.<br>
OpenSIPS sent an INVITE but got no response within the preset time, so it<br>
decides to cancel that branch and try a new one.<br>
The INVITE may have reached its destination - perhaps it was the response<br>
that failed to get back to us.<br>
So it would be correct to send the CANCEL to the same address as the INVITE<br>
- after all, what is there to lose? It might be going into a black hole just<br>
like the INVITE, but that will do no harm. On the other hand it might be<br>
helpful to the target equipment to know that you are no longer interested in<br>
processing the request.<br>
I think this would be correct behaviour according to the RFC's too.<br>
<br>
John Quick<br>
Smartvox Limited<br>
<br>
<br>
<br>
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