f CN entity: For initial attachment, the UE may provide NSSAI to support the selection of an access management function (AMF). If available, NG-RAN uses this information for routing the initial NAS to an AMF. If the NG-RAN is unable to select an AMF using this infor- mation or the UE does not provide any such information, the NG-RAN sends the NAS signaling to one of the default AMFs. - For subsequent accesses, the UE provides a temporary identifier (Temp ID), which is assigned to the UE by the 5GC, to enable the NG-RAN to route the NAS message to the appropriate AMF as long as the Temp ID is valid (NG-RAN is aware of and can reach the AMF that is associated with the Temp ID). Otherwise, the methods for initial attachment apply. Resource isolation between slices: - The NG-RAN supports resource isolation between slices. NG-RAN resource isolation may be achieved by means of RRM policies and protection mechanisms that should prevent the shortage of shared resources in one slice from breaking the SLA for another slice. It should be possible to fully dedicate NG-RAN resources to a certain slice. Access control: - By means of the unified access control (see clause 12.4), operator-defined access cate- gories can be used to enable differentiated handling for different slices. NG-RAN may broadcast barring control information (i.e. a list of barring parameters associated with operator-defined access categories) to minimize the impact of congested slices. Slice availability: - Some slices may be available only in part of the network. The NG-RAN supported S-NSSAI(s) is configured by O&M. Awareness in the NG-RAN of the slices supported in the cells of its neighbors may be beneficial for inter-frequency mobility in connected mode. It is assumed that the slice availability does not change within the UE's registra- tion area. - The NG-RAN and the 5GC are responsible for handling a service request for a slice that may or may not be available in a given area. Admission or rejection of access to a slice may depend on factors such as