5.15.12.2 UE and UE configuration aspects

A UE may support the subscription-based restrictions to simultaneous registration of network slices feature. In this case, the UE indicates its support in the Registration Request message in the Initial Registration and the Mobility Registration Update as part of the UE 5GMM Core Network Capability.

When the serving AMF provides the Configured NSSAI to the UE and the UE has indicated it supports the subscription-based restrictions to simultaneous registration of network slices feature, the AMF also provides the UE with the NSSRG information related to the S-NSSAIs of the HPLMN which are in the mapping information of the Configured NSSAI. A UE which receives the NSSRG values in the network slicing configuration information shall only include in the Requested NSSAI S-NSSAIs that share a common NSSRG as per the received information. If the UE has stored Pending NSSAI and the UE is still interested in the Pending NSSAI then all the S-NSSAIs in the Requested NSSAI and the Pending S-NSSAI shall share a common NSSRG. If the HPLMN changes NSSRG information in the subscription information for a UE, the UDM updates the supporting AMF serving the UE with the new NSSRG information and the AMF, possibly after interaction with the NSSF (see clause 5.2.16.2.1 of TS 23.502 [3]), updates the UE as necessary with network slicing configuration by means of the UE Configuration Update procedure (this may include changes in the Configured NSSAI (and related mapping information) and changes in the Allowed NSSAI as applicable). The UE acknowledges this UE Configuration Update according to clause 4.2.4.2 of TS 23.502 [3].

At any time, a UE supporting subscription-based restrictions to simultaneous registration of network slices feature and that has received NSSRG information together with the Configured NSSAI shall only request S-NSSAIs, across all Access Type(s) regardless of whether the same PLMN or different PLMNs are used, that share one or more common NSSRG.

NOTE: In Requested NSSAI across all Access Type(s), the UE needs to include S-NSSAIs that share at least one common NSSRG.

An AMF which supports the subscription-based restrictions to simultaneous registration of network slice feature configures a non-supporting UE with a Configured NSSAI including only the S-NSSAIs sharing all the NSSRG values of the default S-NSSAI(s), except if it has been instructed otherwise by the UDM. In addition to the default S-NSSAI(s), the AMF sends to the UE in the Configured NSSAI any other subscribed S-NSSAI whose NSSRG match at least those defined for the default S-NSSAI(s).

The UDM in a supporting HPLMN may optionally keep a record of the PEIs or Type Allocation Codes values regarding UE ability to handle network slices that cannot be provided simultaneously in Allowed NSSAI.

The UDM may, based on configuration or the optional PEI records, indicate the AMF to provide the non-supporting UEs with the full set of subscribed S-NSSAIs even if they do not share a common NSSRG. The UDM instructs the supporting AMFs of a PLMN to do so by indicating that the UE can be given a Configured NSSAI with all the S-NSSAIs in the subscription information. If this indication is received from the UDM by the AMF, this is included in the UE context.

Based on its policy (including configuration or optionally checking the specific PEI or Type Allocation Code used by the UE and subject to roaming agreement) the UDM may also provide the serving AMF in a non-supporting VPLMN with all the S-NSSAI in the subscription information. In this case the AMF provides the UE with a Configured NSSAI including all the S-NSSAIs in the subscription information the AMF receives.

The AMF provides no NSSRG information to a non-supporting UE.

When an AMF which supports the subscription-based restrictions to simultaneous registration of network slice feature, receives from a UE a Requested NSSAI including S-NSSAIs that are supported in the Tracking Area but do not share a common NSSRG, or the AMF has pending NSSAI stored for the UE and the S-NSSAI(s) of the requested NSSAI and the pending NSSAI do not share a common NSSRG, the AMF assumes the UE configuration is not up-to-date and provides the following:

• a supporting UE with an updated configuration including the up-to-date NSSRG information for the S-NSSAIs in the Configured NSSAI as described above.
• a non-supporting UE with an updated Configured NSSAI including only the S-NSSAIs sharing all the NSSRG values of the default S-NSSAI(s), only for the case where the UE context does not include an indication to provide all the subscribed S-NSSAIs in the subscription information in the Configured NSSAI for the UE.