 the mapping relationship between S-NSSAIs and RAN part IDs, which could be provided in case registration update request by the RAN node. The principles of RAN subsystem selection are as follows: The UE NAS layer identifies the network slices the UE supports and transfers to UE AS. The UE AS searches the NR frequency bands, and for each carrier frequency identifies the strongest cell that broadcasts S-NSSAIs or RAN part IDs, and tries to camp on the cell. If the UE is not able to identify a suitable cell that supports its associated slices, it seeks to identify an acceptable cell: - a suitable cell is the one for which the measured cell attributes satisfy the cell selection criteria, and the UE's associated RAN subsystem is supported; an acceptable cell is the one for which the measured cell attributes satisfy the cell selec- tion criteria but the cell does not support the UE associated cells. The principles of RAN subsystem reselection for idle and inactive UEs are given as fol- lows: The UE makes measurements of attributes of the serving and neighbor cells to enable the reselection process. The UE will prioritize the frequency band that supports its associated RAN subsystems with the corresponding S-NSSAIs or RAN part IDs. The UE will prioritize the cell that supports its associated RAN subsystems from those cells satisfying the cell reselection criteria. 12 Service-Oriented RAN Support of Network Slicing ((i|') RRC Connection Request SRB 0 (Cause value) RRC Connection Setup SRB 0 (SRB 1 config) RRC Connection Setup Complete SRB 1 (NAS PDU) Security Mode Command SRB 1 procedure Figure 12.9 Transitions from RRC_IDLE to RRC_CONNECTED. 12.4.2 Slice-Specific RAN Part of Network Slice When the UE successfully accesses the network, the RAN may provide slice-specific con- figuration and differentiated handlings to meet the slice requirements and SLA. Figure 12.9 gives the UE transition procedure, which involves the following steps: After the random access procedure with the network, in Message3, the UE may carry the c