[OpenSIPS-Users] 100rel / PRACK Interworking

Fri Nov 14 13:29:05 UTC 2025

Hello Team.

We all agree that PRACK should be supported by the end devices and all agree that PRACK should be supported in order IMS to provide some services. So what is actually happening now on Carrier to Carrier interconnection is the following. In order to be able to interconnect on a carrier exchange, you should comply with a set of specifications. One of those is the PRACK/100rel support. That means that you, as a carrier, must either force your customers to enable PRACK, or do an interworking in the middle. The first option is not feasible as you might have end devices that are not supporting PRACK hence you should find a way to interwork with a device in the middle.

That is why several vendors have implemented modules for PRACK interworking, like bellow

 <https://docs.oracle.com/en/industries/communications/session-border-controller/9.1.0/configuration/sip-prack-interworking.html> https://docs.oracle.com/en/industries/communications/session-border-controller/9.1.0/configuration/sip-prack-interworking.html

I believe that the feature is needed and ideally should be implemented on proxy level. I am willing to contribute on that as this feature is critical for our business.

Regards

Antonis

From: Users <users-bounces at lists.opensips.org> On Behalf Of Aleksei Vasilev
Sent: Παρασκευή, 14 Νοεμβρίου 2025 12:00
To: OpenSIPS users mailling list <users at lists.opensips.org>
Subject: Re: [OpenSIPS-Users] 100rel / PRACK Interworking

Hi colleagues, 

It’s worth mentioning that PRACK (and 200 OK for PRACK) often participates in SDP offer/answer negotiation (RFC 3262, RFC 6337). I’m wondering how this can be implemented solely on the SIP proxy side?

—

Alexey Vasilyev

14 нояб. 2025 г., в 10:39, Johan De Clercq <Johan at democon.be <mailto:Johan at democon.be> > написал(а):

pfff, indeed. 

you save a tiny little bit of networking traffic, that's the only thing that I see. 

okay, 

so the module should contain 

- 200 OK'ing prack. 

- (be able to send prack (?, if there is a use case)). 

- handle update (via rtpprxoy and rtpengine). 

Op vr 14 nov 2025 om 10:33 schreef Giovanni Maruzzelli <gmaruzz at gmail.com <mailto:gmaruzz at gmail.com> >:

> It really is a mess, to me it seems that IMS guys are scared of rtp

+1 it is an endpoint thing, trunk providers are wrong to ask for it (what do they get from it?)

when you (trunk provider) know that the phone is actually ringing, what do you gain? It has meaning when you control the whole chain, end-to-end (carriers, IMS) not at all for deskphone->itsp->trunk->whatever->carrier->endphone

But I know they (trunk providers) start to *REQUIRE* PRACK

So, probably a module, or an extension of an existing module, can be warranted and welcome

Possibly on 3.6.X (that's the last LTS of the 3.0.0 series)

Let's open a thread on what functionalities can be useful in it?

-giovanni

On Fri, Nov 14, 2025 at 10:21 AM Johan De Clercq <Johan at democon.be <mailto:Johan at democon.be> > wrote:

+1.  I totally agree with you. 

It really is a mess, to me it seems that IMS guys are scared of rtp. 

Op vr 14 nov 2025 om 10:03 schreef Walter Schober <walter.schober at neotel.at <mailto:walter.schober at neotel.at> >:

Hi!

I also want to point out that its not done with PRACK handling alone. Followup (multiple) UPDATE with codec changes must be handled, too. Sometimes that lead into AMR(WB)/PCMA/G722/OPUS transcoding in early state. Including all the DTMF PT issues.

It is definitely a endpoint / softswitch feature. 

I know those ignorant IMS guys pushing out their internal mess to plain RFC3261 interconnects and forcing tasks previously done by an MSC to the rest of the world.

Br

Walter  

Von: Users <users-bounces at lists.opensips.org <mailto:users-bounces at lists.opensips.org> > Im Auftrag von Johan De Clercq
Gesendet: Donnerstag, 13. November 2025 16:29
An: gmaruzz at opentelecom.it <mailto:gmaruzz at opentelecom.it> ; OpenSIPS users mailling list <users at lists.opensips.org <mailto:users at lists.opensips.org> >
Betreff: Re: [OpenSIPS-Users] 100rel / PRACK Interworking

Giovanni on a side note, what to do with update ? do you handle it locally or do you forward it to your endpoint ? 

BR, Johan. 

Op do 13 nov 2025 om 15:54 schreef Giovanni Maruzzelli <gmaruzz at gmail.com <mailto:gmaruzz at gmail.com> >:

Antonio, you may want to update this feature request from Johan: https://github.com/OpenSIPS/opensips/issues/2076

On Thu, Nov 13, 2025 at 3:48 PM Antonios Psaras <apsaras at microbase.gr <mailto:apsaras at microbase.gr> > wrote:

Hello Giovanni

I totally agree with you. PRACK is an endpoint feature. But as you know, working with IMS, and having all kind or end point implementations of sip stack you need to do the dirty job in the middle for interoperability reasons. Commercial SBC have that feature called 100rel Interworking which can be enabled per Trunk. Hence, if a carrier requires 100rel/PRACK enforcement and the end point does not supporting it, the function is engaged and handles the PRACK locally.

I will check Bogdan suggestion but in the first read looks like a tmp work around which I am not sure if that can be scaled to few hundreds of CPS that we work with.

As this is a feature that will be needed for VoLTE/5G/IMS networks my suggestion is to create a module for that.

Regards 

From: Giovanni Maruzzelli <gmaruzz at gmail.com <mailto:gmaruzz at gmail.com> > 
Sent: Πέμπτη, 13 Νοεμβρίου 2025 16:37
To: apsaras at microbase.gr <mailto:apsaras at microbase.gr> ; OpenSIPS users mailling list <users at lists.opensips.org <mailto:users at lists.opensips.org> >
Subject: Re: [OpenSIPS-Users] 100rel / PRACK Interworking

El 26/02/2024 a las 7:43 a. m., Bogdan-Andrei Iancu escribió:
> yes, you can use the b2b_logic (together with b2b_entities) for that, 
> but it may be a too heavy tool for the purpose. Maybe you can try to 
> generate the PRACK from OpenSIPS level by using the t_uac_dlg MI 
> function [1] via the mi_script module [2] - basically to trigger that 
> MI cmd from the onreply_route, when receiving the 180 reply.
> 
> [1] https://opensips.org/html/docs/modules/3.4.x/tm.html#mi_t_uac_dlg
> [2] https://opensips.org/html/docs/modules/3.4.x/mi_script.html#afunc_mi 

On Thu, Nov 13, 2025 at 3:34 PM Giovanni Maruzzelli <gmaruzz at gmail.com <mailto:gmaruzz at gmail.com> > wrote:

eg: https://lists.opensips.org/pipermail/users/2024-March/047880.html

On Thu, Nov 13, 2025 at 3:27 PM Giovanni Maruzzelli <gmaruzz at gmail.com <mailto:gmaruzz at gmail.com> > wrote:

Hello Antonio,

PRACK is actually an endpoint feature, at the proxy level you can only fake it...

-giovanni

On Thu, Nov 13, 2025 at 3:14 PM Antonios Psaras <apsaras at microbase.gr <mailto:apsaras at microbase.gr> > wrote:

Dear Team

As many carriers requires 100rel for interoperability reason with IMS, the need for 100rel interworking is mandatory. Is there any solution available to implement that on OpenSIPs Proxy level?

Regards

Antonis Psaras

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-- 

Sincerely,

Giovanni Maruzzelli
OpenTelecom.IT
cell: +39 347 266 56 18

-- 

Sincerely,

Giovanni Maruzzelli
OpenTelecom.IT
cell: +39 347 266 56 18

-- 

Sincerely,

Giovanni Maruzzelli
OpenTelecom.IT
cell: +39 347 266 56 18

-- 

Sincerely,

Giovanni Maruzzelli
OpenTelecom.IT
cell: +39 347 266 56 18

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-- 

Sincerely,

Giovanni Maruzzelli
OpenTelecom.IT
cell: +39 347 266 56 18

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