IMS status in OpenSIPS 3.5

OpenSIPS 3.5 took the challenge of providing a complete support for IMS solutions. And here we are talking about industry grade IMS solutions, exceeding the basic lab grade. So, the target is to provide a robust IMS support to be used in real-life industry solutions.

To achieve this goal, a quite extensive stage of exploring, understanding and designing on the IMS ecosystem is needed – a complex and long term set of tasks to be handled via the IMS OpenSIPS Working Group.

The first task was to understand where we want to get with this IMS support.

Goals

What OpenSIPS 3.5 aims to deliver in terms of IMS support:

• code (OpenSIPS modules) to be implemented in order to provide all the functionalities needed by a decent CSCF IMS component. Here the spectrum is quite large, from new authentication algorithms to DIAMETER or HTTP/s server support. But all these are the base ingredients for building some IMS solution
• working config files, shared with the community, to script OpenSIPS to implement the behavior of all the CSCF components and also to integrate this CSCF with other IMS specific subsystems.

Shortly said, at the end, we should have a simple-to-spin, ready-to-use, docker based CSCF, potentially integrated with a third-party HSS, AS and network layer.

The plan

Understanding the IMS ecosystem, the concepts, the usage cases was a long-run job, started almost 6 months ago. But a mandatory step in order evaluate what needs to be done in order to get to an implementation to be industry adopted.

This part was a community effort, with people involved in discussions and exchange of expertise. Setting up an IMS lab for us was a key step here. Thanks to Voicenter team, to Nitzan and Shlomi Gutman, we got (donated) a first working IMS setup, namely a fully fledged USRP B210 that provides a wide frequency range 70 MHz – 6GHz SDR, allowing us to develop IMS solutions for both 4G and 5G networks.

Also Giovanni Maruzzelli from OpenTelecom.it provided valuable advises on how to build a second testbed based on a Baicells pBS2120 eNB cell that provides access to the 3.5 GHz frequency, allowing us to build a stable IMS system for the 4G network.

Now, armed with two working testbeds, with SIM cards and mobile phones, we have all the ingredients to develop and test our way up. And this was not an easy one, we have to thanks to Carsten Bock from NG-Voice for providing valuable knowledge based on his long expertise in the IMS field.

Status

At this point, with a well defined set of requirements (or goals), we are pushing hard with the development of the various key ingredients of the IMS support:

• the DIAMETER support was well refined for a better data handling
• the AKA authentication is like 90% implemented
• the DIAMETER server support is also 90% ready

What is still on the list:

• HTTP/2 server side support which will be a relatively straight job, considering the fact we already have the DIAMTER similar support
• the IPSEC support for end-device interaction
• some presence extensions to be added.

O course, the big deliverable will be the actual OpenSIPS scripting and integration for CSCF, the point when people will actually have access to a working, consistent IMS support in OpenSIPS.

So stay tune, follow the discussions on the mailing list of the IMS OpenSIPS Working Group. Even better, join us in the process, anybody is more than welcome to contribute with ideas and knowledge here.

Also OpenSIPS 3.5 will be the star of the OpenSIPS Summit 2024 in Valencia, so join us to get the pulse of this new release!