[OpenSIPS-Users] To tag in the CANCEL issue

[Ben Newlin]

CANCELs are hop-by-hop, which means if it is being processed correctly then OpenSIPS will consume the CANCEL from the carrier without a To-tag and generate a new CANCEL to the Cisco client with a To-tag. The issue is that you are not properly “consuming” the CANCEL in OpenSIPS but instead are simply forwarding it.

A CANCEL is considered a sequential request, so it must be passed through the TM module to check if it matches an existing transaction. Take a look at the TM docs for t_check_trans [1]. It provides a reference example of proper CANCEL handling.

[1] - https://opensips.org/docs/modules/3.5.x/tm.html#func_t_check_trans


Ben Newlin

From: Users <users-bounces at lists.opensips.org> on behalf of Alex Balashov <abalashov at evaristesys.com>
Date: Monday, November 25, 2024 at 7:07 AM
To: OpenSIPS users mailling list <users at lists.opensips.org>
Subject: Re: [OpenSIPS-Users] To tag in the CANCEL issue
 EXTERNAL EMAIL - Please use caution with links and attachments

Well, the vendor is just mistaken. ;-)

CANCELs are generated internally by the proxy, since they're a hop-by-hop construct. You're going to have a hard time influencing their content on that level. The vendor's suggestion is, quite frankly, ludicrous.

-- Alex

> On Nov 25, 2024, at 1:16 am, nz deals <nzdealshelp at gmail.com> wrote:
>
> Thanks Alex.
> I raised this issue with Vendor support, and their suggestion was to include the To-tag in the CANCEL request, given that the 180 Ringing and 183 Session Progress responses from the Cisco phone include To-tags. Based on their feedback, they believe the absence of the To-tag in the CANCEL might be contributing to the rejection with a 481 Call/Transaction Does Not Exist error.
> From my observations, my SBC adheres to SIP standards, but since this behavior aligns with Vendor's recommendation and might help address the issue, I wanted to explore this approach as a potential workaround.
>
> Regards,
> Jason
>
> On Mon, 25 Nov 2024 at 17:46, Alex Balashov <abalashov at evaristesys.com> wrote:
> Hi,
>
> Initial INVITEs do not ever have a To-tag. So, the initial INVITE didn't have a To-tag, not because of any quirk or eccentricity, but because initial INVITEs aren't supposed to have To-tags. If the initial INVITE being CANCEL'd doesn't have a To-tag, the CANCEL shouldn't have a To-tag. The CANCEL should not have a To-tag.
>
> I suspect your theory of why the CANCEL is being rejected by the Cisco phone is not correct.
>
> -- Alex
>
> > On Nov 24, 2024, at 10:42 pm, nz deals <nzdealshelp at gmail.com> wrote:
> >
> > Does anyone have any thoughts or input on this?
> >
> > Thanks
> >
> > Regards,
> > Jason
> >
> > On Mon, 18 Nov 2024 at 10:20, nz deals <nzdealshelp at gmail.com> wrote:
> > Hi Community
> > I’m encountering a strange issue with CANCEL requests in my opensips 3.4.2 setup. Here’s the scenario:
> >     • My carrier sends the initial INVITE without a tag in the To header, which I forward to a Cisco phone.
> >     • The Cisco phone responds with a 180 Ringing message, which includes a tag in the To header.
> >     • When I send a CANCEL request, my carrier does not include the tag in the To header, and as a result, OpenSIPS also forwards the CANCEL to the Cisco phone without the tag.
> > Because of this, the Cisco phone responds with a 481 Call/Transaction Does Not Exist error, and the call remains active on the phone without being canceled.
> > I’ve tried modifying the CANCEL request to include the tag in the To header, but I wasn’t able to modify because the initial INVITE doesn’t have a tag in the To header.
> > Has anyone experienced a similar issue or found a way to fix this? Any guidance would be greatly appreciated.
> >
> > Thanks
> >
> > Regards,
> > Jason
> > _______________________________________________
> > Users mailing list
> > Users at lists.opensips.org
> > http://lists.opensips.org/cgi-bin/mailman/listinfo/users
>
> --
> Alex Balashov
> Principal Consultant
> Evariste Systems LLC
> Web: https://evaristesys.com
> Tel: +1-706-510-6800
>
>
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--
Alex Balashov
Principal Consultant
Evariste Systems LLC
Web: https://evaristesys.com
Tel: +1-706-510-6800


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