IMS Working Group Scope

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IMS is a vast concept, with SIP and non-SIP components, and we want to understand and agree on which components of IMS may be subject of work from the OpenSIPS perspective.

The discussion was carried over the group's mailing list here and here.

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The result is summarized here:

• CSCF with all its elements is to be covered (P-CSCF, I-CSCF, S-CSCF) ; we need here to identify the requirements both from SIP perspective and from interaction (with other components) perspective
• AS - it will be very useful to implement such a component, maybe with a relative basic functionality, to serve as a starting point for future extensions; nevertheless, currently we do estimate that the AS related work is mainly scripting and interfacing - no dedicated OpenSIPS features need to be developed here.
• HSS, OCS, MGCF / MGW , PCRF are not part of the scope, still we need to pay some attention from the interfacing perspective.
• the scope should not cover only developing the OpenSIPS code (needed to support an IMS implementation), but also script samples (even if basic ones)

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Notes:

• there were discussions about the NSA and SA models and how they may impact the development here. The agreed conclusion is that this will not impact the actual functionalities we need, but more the logic and interfacing with other components (HSS or PC(R)F). More or less, from OpenSIPS perspective, we need the same set of features, but the scripting will differ (as logic and DIAMETER messages).
• on the AS, MMTel AS should be considered as model - it should provide some predefined logic (like routing between devices, to other networks) with the addition of those listed service - and the settings for the service resides in HSS (via Sh)
• in terms of interfacing protocol, DIAMETER is right now the preferred one, still HTTP/2 should be strongly considered as mandatory for 5G