Device Awareness of RAN Part of Network Slice To support the branded RAN subsystem, the UE should access the 3GPP network as if it were connected to its supported RAN subsystem directly. As Figure 12.7 shows, when the UE registers and accesses the network, it may perform the selection and reselection of the RAN subsystem, and treat the RAN subsystem as its own "private" network. In order to achieve this, the RAN node may broadcast its supported RAN subsystems, to assist the UE to perform RAN subsystem (re)selection. It may also broadcast those neighbor frequency bands and their supported RAN subsystems for inter-frequency subsystem (re)selection. We envision two potential solutions for the UE to be aware of RAN subsystem. An example is given in Figure 12.7. Option 1: Each cell broadcasts its supported S-NSSAIs: The UE tries to access the 3GPP network based on its supported S-NSSAIs and cell broad- casted S-NSSAIs. As the RAN may support hundreds of slices and should ensure scala- bility with more slices in the future, it is essential to reduce the broadcasting overhead. (IIII) Subsystem #1 Subsystem #2 Subsystem #N Figure 12.7 Device awareness of RAN subsystem. 12.4 Key Technologies to Enable Service-Oriented RAN Slicing SST or only part of RAN part ID as Minimum SI The left as on-demand SI via broadcast or dedicated signaling Figure 12.8 UE acquisition of system information. Hence, the RAN node may broadcast the SST as minimum system information (SI), and treat optional SD as other SI either to be broadcast or provisioned in a dedicated manner upon UE request. The UE acquisition of SI is provided in Figure 12.8. Option 2: Each cell broadcasts its supported RAN part IDs: In this option, the UE may map its supported S-NSSAIs to RAN part IDs, and try to camp on those cells that support its supported RAN part IDs. Similar to option 1, this option may treat the essential information of RAN part IDs as minimum SI, and the optional SD as other SI to reduce the broadcast overhead. This option requires the UE to maintain