W.1 General

23.2283GPPIP Multimedia Subsystem (IMS)Release 18Stage 2TS

This clause describes the functions that are used to support IMS services for roaming users in deployments without IMS-level roaming interfaces. This annex is applicable to UEs connected to EPS and 5GS. In this roaming model the mobility anchor (i.e. PGW or UPF) is located in the home PLMN and therefore UE IMS signalling and user plane traffic are routed to home PLMN. It is assumed that confidentiality protection is not used in HPLMN and VPLMN for IMS media plane traffic.

For the LBO roaming model where P-CSCF is in VPLMN, see Annex M.