<div dir="ltr">Despite what the RFC states, some SBCs (Sansay) will send CANCEL even if no provisional response has been received. This can prevent billing disputes in cases where a 200 OK to the INVITE would have been sent but not received. It can also be helpful in troubleshooting to see whether the far end responds with 481 to the CANCEL, 487 Request Terminated to the INVITE with 200 to the CANCEL, or not at all.<br clear="all"><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><span><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:10pt;font-family:"Proxima Nova",sans-serif;color:rgb(0,0,0);background-color:transparent;font-weight:800;vertical-align:baseline;white-space:pre-wrap"><br></span></p><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:10pt;font-family:"Proxima Nova",sans-serif;color:rgb(0,0,0);background-color:transparent;font-weight:800;vertical-align:baseline;white-space:pre-wrap"><br></span></p><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:10pt;font-family:"Proxima Nova",sans-serif;color:rgb(0,0,0);background-color:transparent;font-weight:800;vertical-align:baseline;white-space:pre-wrap">Calvin Ellison</span></p><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:10pt;font-family:"Proxima Nova",sans-serif;color:rgb(0,0,0);background-color:transparent;vertical-align:baseline;white-space:pre-wrap">Systems Architect</span></p><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:10pt;font-family:"Proxima Nova",sans-serif;color:rgb(0,0,0);background-color:transparent;vertical-align:baseline;white-space:pre-wrap"><a href="mailto:calvin.ellison@voxox.com" target="_blank">calvin.ellison@voxox.com</a></span></p><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:2.25pt;font-family:"Proxima Nova",sans-serif;color:rgb(0,0,0);background-color:transparent;vertical-align:baseline;white-space:pre-wrap"><br></span></p><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><a href="http://voxox.com" target="_blank"><span style="font-size:10pt;font-family:"Proxima Nova",sans-serif;color:rgb(17,85,204);background-color:transparent;vertical-align:baseline;white-space:pre-wrap"><span style="border:none;display:inline-block;overflow:hidden;width:139px;height:53px"><img src="https://lh5.googleusercontent.com/IpUfF3j5Y4T9UmEfLISsHXhgSenc131vheivxwdo6oyzyT1i5KfVnK8cftA1Qx-APliNpMTLx5PUOZ6k1lXHgMZvDXTXKkOWDpmXMlUcmsoKBZQIE_wip4sS8XMtdryakordMboW" width="139" height="53" style="margin-left:0px;margin-top:0px"></span></span></a></p><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><a href="https://www.facebook.com/VOXOX/" target="_blank"><span style="font-size:12pt;font-family:"Proxima Nova",sans-serif;color:rgb(17,85,204);background-color:transparent;vertical-align:baseline;white-space:pre-wrap"><span style="border:none;display:inline-block;overflow:hidden;width:27px;height:27px"><img src="https://lh6.googleusercontent.com/qS_cwPUkKDN7UEAMffT5cjE1qN41OWxwS8HKu2DZi8R9OfYZCrdVxxPsyJy_SOaTDjWHjPAsBAzGnrgiSgrqDFWQKoi1HAdYUldZOtUQY_2EH0FC7M67fPko4xEmw7yfwiIpnRIF" width="27" height="27" style="margin-left:0px;margin-top:0px"></span></span></a><span style="font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;vertical-align:baseline;white-space:pre-wrap"> </span><a href="https://www.instagram.com/voxoxofficial/" target="_blank"><span style="font-size:12pt;font-family:"Proxima Nova",sans-serif;color:rgb(17,85,204);background-color:transparent;vertical-align:baseline;white-space:pre-wrap"><span style="border:none;display:inline-block;overflow:hidden;width:26px;height:26px"><img src="https://lh3.googleusercontent.com/AFGDGW3w1Yco24kAphoI6UZW170z44YjZpLZ0rHGRfCDNyctuD4DkIYooDbxEoJxrv0NQ4TswSWA4k0FPOD6w5v_ZFadQmeoXHhP1rgeZXdoLV7n-1PGxYhi31pbte1GHYwURny8" width="26" height="26" style="margin-left:0px;margin-top:0px"></span></span></a><span style="font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;vertical-align:baseline;white-space:pre-wrap"> </span><a href="https://www.linkedin.com/company/3573541/admin/" target="_blank"><span style="font-size:12pt;font-family:"Proxima Nova",sans-serif;color:rgb(17,85,204);background-color:transparent;vertical-align:baseline;white-space:pre-wrap"><span style="border:none;display:inline-block;overflow:hidden;width:26px;height:26px"><img src="https://lh6.googleusercontent.com/skcophrAnEg1jyCTXau3hMbh0GF9b1TeZ-SdROEZ0OxxHuTRKGNTS_lYIh2LIdgJ6rLTL1LMUVOlhxrHm7hxZ6p8XfYovu7xd-tXhvU1OEm4Hi6niWF6Trr7EfMFqGoLNMMeyYqk" width="26" height="26" style="margin-left:0px;margin-top:0px"></span></span></a><span style="font-size:11pt;font-family:Arial;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<br>
Yes, you're right. Section 9.1 of RFC3261 says "If no provisional response<br>
has been received, the CANCEL request MUST NOT be sent"<br>
<br>
So then it is a question the developers will need to answer, although from a<br>
practical point of view I doubt that it would cause a problem for the<br>
reasons I gave.<br>
<br>
John Quick<br>
Smartvox Limited<br>
<br>
> From: Ben Newlin <<a href="mailto:Ben.Newlin@genesys.com" target="_blank">Ben.Newlin@genesys.com</a>> <br>
> Sent: 30 June 2021 16:25<br>
> To: <a href="mailto:john.quick@smartvox.co.uk" target="_blank">john.quick@smartvox.co.uk</a>; OpenSIPS users mailling list<br>
<<a href="mailto:users@lists.opensips.org" target="_blank">users@lists.opensips.org</a>><br>
> Cc: <a href="mailto:solarman@one-n.co.uk" target="_blank">solarman@one-n.co.uk</a><br>
> Subject: Re: [OpenSIPS-Users] fr_timeout CANCEL message sent to timed out<br>
dispatcher endpoint IP<br>
><br>
> I'm pretty sure the RFCs state that a CANCEL should only be sent if some<br>
response, usually 100 Trying, has been received. This is to avoid the<br>
possibility of the INVITE and CANCEL > being received out of order at the<br>
destination.<br>
><br>
> Ben Newlin <br>
<br>
<br>
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</blockquote></div>