Y.1 Mobility related concepts

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

Y.1.0 General

To support IMS, the UE shall establish a PDU session with PDU session type set to IP for the corresponding DNN (see TS 23.501 [93], clause 5.6.1), and acquire an IP address according to TS 23.501 [93], clause 5.8.2.2. If IMS Multimedia Telephony Service as specified in TS 22.173 [53] is to be used within the PDU session, SSC mode 1 shall be set for the PDU session. In this release of the specification, it is assumed that single PDU session with multiple PDU session anchors defined in TS 23.501 [93] clause 5.6.4 is not applicable for PDU sessions dedicated to IMS.

NOTE 1: In the case of Dual Registration as defined in TS 23.501 [93], the UE will register (and if needed re-register) in IMS with the IP address of the IMS PDU session when the IMS PDU session is transferred between 5GS and EPS.

If the UE changes its IP address due to changes triggered by the 5GS procedures or due to, for example, PLMN change, then the UE shall re- register in the IMS.

If the UE acquires an additional IP address, then the UE may perform an IMS registration using this additional IP address as the contact address. If IMS registration is performed, this IMS registration may co-exist with the previous IMS registration from this UE and the UE shall be notified that this IMS registration results in multiple simultaneous registrations.

NOTE 2: In this Release of the specification, the UE can acquire an additional IP address that can be used for registration to the IMS only outside of the 5G System.

In Dual Connectivity with 5GC case, the UE shall use the access network information based on the primary cell of the Master RAN node that is serving the UE for network location information when the UE interacts with IMS, regardless whether the IMS traffic is routed via the Master RAN node or the Secondary RAN node or both.

Y.1.1 Procedures for P‑CSCF discovery

All the procedures described in clause 5.1.1 apply with the following additions:

– For the option where P-CSCF discovery is part of the IP-CAN connectivity establishment the following applies:

– P‑CSCF discovery shall take place during the PDU session establishment procedure see TS 23.502 [94], clause 4.3.2.

In addition to the procedures in clause 5.1.1, the SMF may determine the P-CSCF using service-based discovery methods (using the NRF), as described in TS 23.501 [93] clause 5.16.3.