5.15.14 Network Slice AS Groups support

The NG-RAN may support Network Slice AS Groups (NSAGs) which are used as specified in TS 38.300 [27], TS 38.331 [28], TS 38.321 [143] and TS 38.304 [50]. A Network Slice AS Group is an identifier of a group of network slices which are associated with it. A Network Slice AS Group association with a group of network slices may be valid in one or more Tracking Areas. An S-NSSAI can be associated with at most one NSAG values for Random Access and at most one NSAG value for Cell Reselection within a Tracking Area. An S-NSSAI can be associated with different NSAG values in different Tracking Areas.

The NG-RAN provides (and updates) the AMF with the values of the NSAG(s) an S-NSSAI is associated with in a TA using the NG Set Up and RAN Configuration Update procedures (see TS 38.413 [34]). The AMF in turn provides this information to the NSSF. In deployments where the total number of groups does not exceed the number of groups associated with the NSAG size limit defined in TS 38.331 [28]), all the NSAGs configured in the NG-RAN may be unique per PLMN or SNPN. If the UE has indicated that the UE supports NSAG in the 5GMM Core Network Capability (see clause 5.4.4a), the AMF may, with or without NSSF assistance, configure the UE with NSAG Information for one or more S-NSSAIs in the Configured NSSAI, by including this NSAG Information in the Registration Accept message or the UE Configuration Command message. The UE uses the NSAG Information as defined in clause 5.3.4.3.1. The AMF shall indicate in the NSAG Information in which TA a specific NSAG association to S-NSSAI(s) is valid if the AMF provides in the UE configuration a NSAG value which is used in different TAs with a different association with NSSAIs. The configuration the AMF provides includes at least the NSAGs for the UE for the TAs of the Registration Area. If the AMF does not include the list of TAIs in association with an NSAG in the NSAG Information, the NSAG is valid in the Registered PLMN and equivalent PLMNs, or SNPN.

NOTE: If the NSAGs for the PLMN and equivalent PLMNs have different associations to S-NSSAIs, then the AMF includes the list of TAIs in the NSAG information.

The UE shall store and consider the received NSAG Information, valid for the Registered PLMN and equivalent PLMNs, or SNPN until:

• the UE receives new NSAG information in a Registration Accept message or UE Configuration Command message in this PLMN or SNPN; or
• the UE receives a Configured NSSAI without any NSAG information in this PLMN or SNPN.

The UE shall store the currently valid NSAG information received in the Registered PLMN or SNPN when registered in this PLMN or SNPN and:

• The UE should be able to store the NSAG information for at least the Registered-PLMN and equivalent PLMNs, or the Registered-SNPN and equivalent SNPNs.
• The Registered-PLMN can provide NSAG information to the UE for the PLMN and the equivalent PLMNs and the Registered-SNPN can provide NSAG information to the UE for the SNPN.
• There can be at most 32 NSAGs configured in the UE at a time for a PLMN or SNPN.
• At most 4 NSAGs can have an optional TAI associated with it.

The NSAG information is not required to be stored after power off or after the UE becomes Deregistered as it is not used for cell selection.