5.35A.3.1 UE mobility between a fixed cell and MBSR cell

For UEs in RRC_IDLE and RRC_INACTIVE state when a MBSR goes out-of-service, procedure for cell (re)selection as specified in TS 38.304 [50] for RRC_IDLE and RRC_INACTIVE is used between MBSR cell and other cells.

If the MBSR goes out-of-service (due to e.g. MBSR moves to an area where the MBSR is not allowed to provide the relay service), the NG-RAN triggers the handover procedures to the neighbouring cells for UEs in RRC_CONNECTED state served by the MBSR. Any change of authorization state of the MBSR is also handled according to clause 5.35A.4.

The IAB-donor-CU triggers handover procedure when it is possible for the UEs accessing emergency service and being served by the MBSR, if MBSR is about to become unavailable to provide the services.