The 5GC enables traffic to route via localized UPF close to the edge of the network (in some cases adjacent to the RAN nodes). Some IMS services may be able to benefit from the lower latency and/or lower backhaul requirements that such deployments can enable, however current IMS applications and services are not able to leverage these capabilities. This key issue investigates the interactions required to leverage localized routing of IMS media and signalling traffic, the changes to enable effective control and management of such routing, and impacts of mobility and roaming.

The existing 5GC and IMS architecture does not specifically support having user plane and IMS media plane entities in the same location and hence user plane path handling is not optimized. To optimise the user plane path, a location of the MGCF and MRF close to the actual UPF (that the user plane needs to traverse) is desirable. For instance, UPF and MGCF could be located in the same data centre. When selecting an MGCF or MRF, IMS nodes shall be enabled to base this selection on the actually used UPF. The solutions to this key issue may take additional IMS nods (e.g. IMS-AGW, ATGW and TrGW) into account.

All of the 5GC control plane NFs are specified as service based and any NF can be consumer of the services provided by other NFs, if supported by the procedures.

This key issue addresses IMS and 5GC service interfaces aspects on:

• How IMS can utilize services provided by 5GC NFs other than PCF.
• How to determine the UE location in IMS entities with service operations (e.g. determination of the visited PLMN ID in case of Home-Routed VoLTE roaming).