Deploying Vo5G/VoNR by allowing the implementation of IMS core components into the 5G Service Based Architecture (SBA).
This 3GPP “Study on enhanced IP Multimedia Subsystem (IMS) to 5GC integration”, an exploratory technical report published as TR 23.794 for EIMS.
TR 23.794 goes into great detail about augmenting and replacing Diameter interfaces with Service Based Interfaces (SBIs). This allows a 5G IMS core to support not only existing Producers (to use Service Oriented Architecture terminology) but newer, 5G-specific, network functions deployed within the SBA. As might be the case with our interworking approach, this could also include hybrid implementations, where a classic Home Subscriber Server (HSS) is located via the Network Function (NF) Repository Function (NRF) using an SBI Nnrf_NFDiscovery_Request message which then dips the current HSS database via a proxy.
This would extend to each distinct cloud native IMS Core network function exposing a Cx or Dx interface to the HSS or a Subscription Locator Function (SLF), namely the consuming P/I/S-CSCFs. The ultimate goal is to facilitate a smooth migration to the SBA’s Unified Data Management (UDM) Service. Likewise, supporting network functions with a Diameter-based reference interface, such as applications servers (Sh) and Policy Control Functions (Rx) must move towards SBI’s, as those NFs evolve to embrace cloud native characteristics. The 3GPP study explores the mapping of Cx and Dx messages to existing SBI Nudm operations and replacing all diameter interfaces, currently defined within TS 29.228 and TS 29.229, with new IMS services with a Nhss_ims_ prefix.