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Content for  TR 23.794  Word version:  17.0.0

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1  ScopeWord‑p. 8

The aim of this Technical Report is to study and specify potential enhancements to the IMS architecture to enable IMS FE to integrate with the 5GC network functions to enable IMS applications to directly leverage the features and capabilities of 5GC.
The specific capabilities of 5GC included in this study:
  • In regard to 5GC network slicing; what enhancements (if any) are necessary for IMS to efficiently support devices and networks with multiple slices and different IMS services per slice?
  • Should (and How does) IMS leverage the 5GC's support for localized routing of traffic and placement of IMS elements? How do such optimizations impact IMS media bearers, IMS signalling bearers, and IMS functions? How is service continuity provided in presence of localized routing?
  • Whether and how can IMS applications and network functions utilize the service based capabilities and service based interfaces of the 5GC (for interactions between the IMS and the 5GC)? Which 5GC functions should be interfaced with IMS using service based interfaces?

2  References

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
  • References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
  • For a specific reference, subsequent revisions do not apply.
  • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
TR 21.905: "Vocabulary for 3GPP Specifications".
TS 23.228: "IP Multimedia Subsystem (IMS); Stage 2".
TS 23.501: "System Architecture for the 5G System".
TS 23.502: "Procedures for the 5G System".
TS 23.503: "Policy and Charging Control Framework for the 5G System; Stage 2".
TS 23.237: "IP Multimedia Subsystem (IMS) Service Continuity; Stage 2".
TS 23.203: "Policy and charging control architecture".
RFC 6665:  "SIP-Specific Event Notification".
TS 29.329: "Sh Interface based on Diameter - Protocol details".
TS 29.228: "IP Multimedia (IM) Subsystem Cx and Dx interfaces; Signalling flows and message contents".
TS 29.229: "Cx and Dx interfaces based on the Diameter protocol; Protocol details".
TS 23.167: "IP Multimedia Subsystem (IMS) emergency sessions".
TS 29.328: "IP Multimedia (IM) Subsystem Sh interface; Signalling flows and message contents".

3  Definitions and abbreviationsWord‑p. 9

3.1  Definitions

For the purposes of the present document, the terms and definitions given in TR 21.905, and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905.

3.2  Abbreviations

For the purposes of the present document, the abbreviations given in TR 21.905, TS 23.228, TS 23.501 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905.
5G Core
5G System
Access Gateway
Branching Point
Circuit Switched Routing Number
Functional Entity
Globally Routable User Agent URI
Interrogating CSCF
IMS Application Server IMS FE IMS Functional Entity
IP Exchange
Local Breakout
Multi Media Telephony
Proxy CSCF
PDU Session Anchor
Session Anchor
Serving CSCF
Service Continuity Control Application Server TADS Terminating Access Domain Selection
Uplink Classifier
Uplink Classifier

4  Architecture Assumptions

The following architectural assumptions are applicable for all potential solutions:
  • IMS architecture defined is TS 23.228 (release 15) is the baseline, especially with regard to usage of SIP signalling.
  • The IMS Service Based Cx, Dx, Sh are produced logically by the HSS, so the functional allocation of the IMS service logic to HSS is in line with TS 23.228.
  • All existing IMS architectural models (e.g. TS 23.228, TS 23.237, etc.) shall be supported
  • SIP signalling is used between UE and IMS Network

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