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

[Ben Newlin]

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

From: Users <users-bounces at lists.opensips.org> on behalf of John Quick <john.quick at smartvox.co.uk>
Date: Wednesday, June 30, 2021 at 11:19 AM
To: users at lists.opensips.org <users at lists.opensips.org>
Cc: solarman at one-n.co.uk <solarman at one-n.co.uk>
Subject: Re: [OpenSIPS-Users] fr_timeout CANCEL message sent to timed out dispatcher endpoint IP
That sounds like reasonable behaviour to me, at least for UDP.
OpenSIPS sent an INVITE but got no response within the preset time, so it
decides to cancel that branch and try a new one.
The INVITE may have reached its destination - perhaps it was the response
that failed to get back to us.
So it would be correct to send the CANCEL to the same address as the INVITE
- after all, what is there to lose? It might be going into a black hole just
like the INVITE, but that will do no harm. On the other hand it might be
helpful to the target equipment to know that you are no longer interested in
processing the request.
I think this would be correct behaviour according to the RFC's too.

John Quick
Smartvox Limited



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