4.5 Mobility related concepts

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

The following procedures are supported by an UE when accessing IMS:

– Connect to the IP‑CAN and acquire the necessary IP address, which includes, or is followed by, the P‑CSCF discovery procedure. The mobility related procedures and IP address management principles for the IP‑CAN are described in the relevant IP‑CAN specifications;

– Register to the IM subsystem as defined by the IMS registration procedures;

– If an UE explicitly deactivates the IP‑CAN bearer that is being used for IMS signalling, it shall first de-register from the IMS (while there is no IMS session in progress);

– If an UE explicitly deactivates the IP‑CAN bearer that is being used for IMS signalling while an IMS session is in progress, the UE must first release the session and de-register from the IMS and then deactivate the IP‑CAN bearers;

– If an UE changes its IP address according to IP‑CAN procedures (e.g. TS 23.221 [7]), the UE shall re- register in the IMS by executing the IMS registration;

– If an UE acquires an additional IP address due to establishing an additional IP‑CAN bearer through a different access network, the UE may perform an IMS registration using this 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.

– In order to be able to deliver an incoming IMS session, the IP‑CAN bearer that is being used for IMS signalling need to remain active as long as the UE is registered in the IM CN subsystem;