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.
Calvin Ellison Systems Architect [email protected] <http://voxox.com> <https://www.facebook.com/VOXOX/> <https://www.instagram.com/voxoxofficial/> <https://www.linkedin.com/company/3573541/admin/> <https://twitter.com/Voxox> The information contained herein is confidential and privileged information or work product intended only for the individual or entity to whom it is addressed. Any unauthorized use, distribution, or copying of this communication is strictly prohibited. If you have received this communication in error, please notify me immediately. On Wed, Jun 30, 2021 at 8:59 AM John Quick <[email protected]> wrote: > Ben, > > Yes, you're right. Section 9.1 of RFC3261 says "If no provisional response > has been received, the CANCEL request MUST NOT be sent" > > So then it is a question the developers will need to answer, although from > a > practical point of view I doubt that it would cause a problem for the > reasons I gave. > > John Quick > Smartvox Limited > > > From: Ben Newlin <[email protected]> > > Sent: 30 June 2021 16:25 > > To: [email protected]; OpenSIPS users mailling list > <[email protected]> > > Cc: [email protected] > > Subject: Re: [OpenSIPS-Users] fr_timeout CANCEL message sent to timed out > dispatcher endpoint IP > > > > 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. > > > > Ben Newlin > > > _______________________________________________ > Users mailing list > [email protected] > http://lists.opensips.org/cgi-bin/mailman/listinfo/users >
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