Section: 5.2.16.2.1 Nnssf_NSSelection_Get service operation
Content: Service operation name: Nnssf_NSSelection_Get Description: This service operation enables Network Slice selection in both the Serving PLMN and HPLMN. It also enables the NSSF to provide to the AMF the Allowed NSSAI and the Configured NSSAI for the Serving PLMN. It allows also to provide the NSAG information which is applicable (clause 5.15.14 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]). It may be invoked during Registration procedure, during inter-PLMN mobility procedure, during PDU Session Establishment procedure or during UE Configuration Update procedure. When invoked during Registration procedure it may possibly trigger AMF re-allocation. When invoked during PDU Session Establishment procedure it may be invoked in the VPLMN or in the HPLMN; if invoked in the VPLMN it returns the hNRF selected by the hNSSF and if applicable, the value of the HPLMN NSI ID. When invoked during UE Configuration Update procedure or inter-PLMN mobility procedure it may be invoked in the Serving PLMN. NOTE 1: The list of events, which trigger invoking of the Nnssf_NSSelection_Get service operation, is not exhaustive. NOTE 2: The NSSF can determine the serving network and Access Type from the TAI, as described in TS 29.571[ 5G System; Common Data Types for Service Based Interfaces; Stage 3 ]  [70]. Inputs, Required: None. Inputs, Conditional Required: If this service operation is invoked during Registration procedure for Network Slice selection or UE Configuration Update procedure, then the following inputs are required: - Subscribed S-NSSAI(s) with the indication if marked as default S-NSSAI, PLMN ID of the SUPI, TAI, NF type of the NF service consumer, Requester ID. If this service operation is invoked to derive the S-NSSAI for the serving PLMN (as described in clause 4.11.1.3.3), the following inputs are required: - S-NSSAIs for the HPLMN associated with established PDN connection, PLMN ID of the SUPI, NF type of the NF service consumer, Requester ID. If this service operation is invoked by target AMF during inter-PLMN mobility procedure, the following inputs are required: - S-NSSAIs for the HPLMN, PLMN ID of the SUPI, TAI. If this service operation is invoked during PDN Connection Establishment in the Serving PLMN in EPS by a SMF+PGW-C, the following inputs are required: - Subscribed S-NSSAIs for the UE, PLMN ID of the SUPI, NF type of the NF service consumer, Requester ID. If this service operation is invoked during PDU Session Establishment procedure in the Serving PLMN then the following inputs are required: - S-NSSAI, non-roaming/LBO roaming/HR roaming indication, PLMN ID of the SUPI, TAI, NF type of the NF service consumer, Requester ID. Inputs, Optional: If this service operation is invoked during Registration procedure for Network Slice selection or UE Configuration Update procedure, then the following inputs are provided if available: - Requested NSSAI, Mapping Of Requested NSSAI, Default Configured NSSAI Indication, NSSRG Information, UE support of subscription-based restrictions to simultaneous registration of network slice feature Indication, UDM indication to provide all subscribed S-NSSAIs for UEs not indicating support of subscription-based restrictions to simultaneous registration of network slices, Allowed NSSAI for current Access Type, Allowed NSSAI for the other Access Type and the corresponding Mapping Of Allowed NSSAIs for current Access Type and other Access Type, Rejected S-NSSAI(s) for RA, UE support of NSAG Information. If this service operation is invoked during PDU Session Establishment procedure, then the following input is optional: - HPLMN S-NSSAI that maps to the S-NSSAI from the Allowed NSSAI of the Serving PLMN. Outputs, Conditional Required: If this service operation is invoked during Registration procedure for Network Slice selection or UE Configuration Update procedure, then one or more of the following outputs are required: - Allowed NSSAI, Configured NSSAI; Target AMF Set or, based on configuration, the list of candidate AMF(s). If this service operation is invoked during inter-PLMN mobility procedure, then one or more of the following outputs are required: - Allowed NSSAI. If this service operation is invoked to derive the S-NSSAI for the serving PLMN (as described in clause 4.11.1.3.3), the following output is required: - S-NSSAIs for the HPLMN associated with established PDN connection, Mapping of S-NSSAIs associated with established PDN connection in the Serving PLMN. If this service operation is invoked during PDN Connection Establishment in the Serving PLMN in EPS by a SMF+PGW-C, the following outputs are required: - Subscribed S-NSSAIs for the UE, Mapping of S-NSSAIs associated with the subscribed S-NSSAIs for the UE in the Serving PLMN. If this service operation is invoked during PDU Session Establishment procedure, then the following outputs are required: - The NRF to be used to select NFs/services within the selected Network Slice instance. Outputs, conditional Optional: If this service operation is invoked during UE Registration procedure or UE Configuration Update procedure, then one or more of the following outputs are optional: - Mapping Of Allowed NSSAI, Mapping Of Configured NSSAI, NSI ID(s) associated with the Network Slice instances of the Allowed NSSAI, NRF(s) to be used to select NFs/services within the selected Network Slice instance(s) and NRF to be used to determine the list of candidate AMF(s) from the AMF Set, rejected S-NSSAI with cause of rejection, Target NSSAI, the NSAG information (defined in clause 5.15.14 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]). If this service operation is invoked during inter-PLMN mobility procedure, then the following output is optional: - Mapping Of Allowed NSSAI. If this service operation is invoked during PDU Session Establishment procedure, then the following output is optional: - NSI ID associated with the S-NSSAI provided in the input.