4.15b Roaming Architecture for Voice over IMS with home routed traffic
23.2283GPPIP Multimedia Subsystem (IMS)Release 18Stage 2TS
In this scenario, the anchor point for the IP address for both the IMS signalling and media traffic is in the home network for a roaming UE, i.e. for 3GPP systems, the GGSN, PGW or UPF for a roaming UE is in the HPLMN of the UE.
The following architecture requirements apply:
– The P-CSCF is located in the HPLMN
Additional architecture requirements and functions that are needed to support IMS services with home routed traffic are depicted in Annex W for EPS and in Annex Y for 5GS.