6.3.17 NSSAAF discovery and selection

23.5013GPPRelease 18System architecture for the 5G System (5GS)TS

In the case of NF consumer based discovery and selection, the following applies:

– The NF consumer (e.g. AMF, AUSF) performs NSSAAF selection to select an NSSAAF Instance that supports authentication between the UE and the AAA-S associated with the HPLMN or in the Credentials Holder in the case of SNPN or in the DCS domain in the case of ON-SNPN. The NF consumer shall utilize the NRF to discover the NSSAAF instance(s) unless NSSAAF information is available by other means, e.g. locally configured on the NF consumer. The NSSAAF selection function in the NF consumer selects an NSSAAF instance based on the available NSSAAF instances (obtained from the NRF or locally configured in the NF consumer).

In the case of SNPN, NSSAAF selection is only applicable to 3GPP access. Otherwise, NSSAAF selection is applicable to both 3GPP access and non-3GPP access.

The NSSAAF selection function in NSSAAF NF consumers or in SCP should consider the following factor when it is available:

1. Home Network Identifier (e.g. MNC and MCC, realm) of SUPI (by an NF consumer in the Serving network).

2. S-NSSAI of the HPLMN.

3. SUPI or Internal Group ID; the NSSAAF NF consumer selects a NSSAAF instance based on the SUPI range the UE’s SUPI belongs to or based on the results of a discovery procedure with NRF using the UE’s SUPI or Internal Group ID as input for NSSAAF discovery.

An HPLMN deploying NSSAAF instances supporting specific S-NSSAIs and/or sets of SUPIs (according to factors 2-3) shall also deploy NSSAAF instance(s) that can be selected using factor 1 if they need to interoperate with VPLMNs using only factor 1 for NSSAAF selection.

In the case of delegated discovery and selection in SCP, the NSSAAF NF consumer shall send all available factors to the SCP.