2.14 shows, the RAN can try to ensure service continuity. For example, some slicing mapping policies could be predefined, and the traffics could be switched to another slice for data continuity. 12 Service-Oriented RAN Support of Network Slicing ((i||)) Subsystem 1 Subsystem 2 Inter-slice mapping Figure 12.14 Slice service continuity during inter-cell handover. gNB1 in Registration Area 1 gNB2 in Registration Area 2 UE in active mode with n slices configured at NAS-level and with m PDU Sessions active at AS level Slice aware handover preparation from gNB 1 to gNB 2 triggered 1. Handover Request (PDU Session + S-NSSAI List) 2. Slice mapping if with mapping poloicy 3. Handover Request Ack (List of accepted and rejected PDU Session + S-NSSAI) 4. Handover Execution 5. Path Switch Request (mapped S-NSSAI) 6. Path Switch Request Ack 7. Registration Area Update (alignment of slices supported in the new RA between UE and network) Figure 12.15 Xn based inter-cell handover. The detailed network interface between gNBs (next generation NodeB) based handover is given in Figure 12.15. When gNB2 finds that the active PDU sessions associated with S-NSSAI#1 are not supported, based on the mapping policy as one of the UE contexts, it could map the S-NSSAI#1 to S-NSSAI#2, SO that the service continuity of S-NSSAI#1 is ensured. 12.5 Summary UE registration Subsystem 1 (11|1)) Subsystem 2 Subsystem 1 Figure 12.16 Illustration of UE RA with nonuniform RAN subsystems. 12.4.5 Slice-Level Handlings for Idle/Inactive UEs Paging procedure: As discussed above, the UE's registration area is not coupled with the UE-supported network slices. Hence, within the UE's routing area (RA), different RAN nodes support different RAN subsystems. When the CN initiates a paging message, it may happen that the RAN node does not support the CN's initiated PDU sessions of network slices. One example is given in Figure 12.16, where the paging procedure is initiated by S-NSSAI cor- responding with RAN subsystem1 while the UE is located in the coverage of subsy