[OpenSIPS-Users] fr_timeout CANCEL message sent to timed out dispatcher endpoint IP

[Calvin Ellison]

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

calvin.ellison at voxox.com


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On Wed, Jun 30, 2021 at 8:59 AM John Quick <john.quick at smartvox.co.uk>
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 <Ben.Newlin at genesys.com>
> > Sent: 30 June 2021 16:25
> > To: john.quick at smartvox.co.uk; OpenSIPS users mailling list
> <users at lists.opensips.org>
> > Cc: solarman at one-n.co.uk
> > 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
>
>
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