6.3.6.2a SNPN N3IWF selection

This procedure applies when the UE is accessing the SNPN N3IWF in its subscribed SNPN via a PLMN or directly via untrusted non-3GPP access.

The UE shall first determine the country in which it is located. If the UE cannot determine the country in which the UE is located, the UE shall stop N3IWF selection and abort the attempt to access the SNPN via PLMN.

NOTE 1: It is up to UE implementation how to determine the country in which the UE is located.

The UE is configured with one N3IWF address and the MCC of the country where the configured N3IWF is located as defined in TS 24.502 [48].

If the UE determines that it is located in the country where the configured N3IWF is located, then the UE uses the configured N3IWF FQDN to select an N3IWF deployed in the SNPN.

If the UE determines that it is located in a country (called the visited country) different from the country where the configured N3IWF is located, then:

• The UE shall construct an FQDN consisting of the SNPN ID of the subscribed SNPN and the Visited Country FQDN and indicating the query is for SNPN, as specified in TS 23.003 [19] and perform a DNS query for the resulting FQDN.
• If the DNS response contains no records, then the UE determines that the visited country does not mandate the selection of an N3IWF in this country for the SNPN identified by the SNPN ID provided by the UE. In this case the UE uses the configured N3IWF FQDN to select an N3IWF deployed in the SNPN.
• If no DNS response is received, the UE shall stop the N3IWF selection.

NOTE 2: The DNS can be configured to return no records for the visited country regardless of the SNPN ID provided by the UE. This addresses the scenario that the visited country in general does not mandate selection of a local N3IWF.

• If the DNS response contains one or more records, then the UE determines that the visited country mandates the selection of an N3IWF in this country. Each record in the DNS response shall contain the identity of an N3IWF of the UE's subscribed SNPN in the visited country which may be used for N3IWF selection. In this case:
• The UE shall select an N3IWF included in the DNS response based on its own implementation means.
• If the UE cannot select any N3IWF included in the DNS response, then the UE shall stop the N3IWF selection.

NOTE 3: Visited countries which mandate the selection of an N3IWF in the country are assumed to configure the DNS as follows:

(i) For SNPNs that do not have any dedicated N3IWFs in the country and which are not exempt from the requirement to select an N3IWF in the visited country, the DNS response contains a record that cannot be resolved to an IP address;

(ii) for SNPNs that have dedicated N3IWFs in the country, the DNS response contains the identities of the SNPN's N3IWFs in the visited country;

(iii) for SNPNs that are exempt from the requirement to select an N3IWF in the visited country, the DNS response contains no records.

NOTE 4: Self-assigned NIDs are not supported, since a DNS cannot be properly configured for multiple SNPNs using the same self-assigned NID (i.e. in collision scenarios). If the visited country mandates the selection of an N3IWF in the same country, the NAPTR record(s) associated to the Visited Country FQDN of SNPNs that use a self-assigned NID can be provisioned with the replacement field containing an FQDN that cannot be resolved to an IP address.

NOTE 5: The identity of an SNPN's N3IWF in the visited country can be any FQDN, i.e. is not required to include the SNPN ID.

NOTE 6: It is assumed that the AMF, SMF, UPF are located in the same country as the N3IWF and belong to the subscribed SNPN of the UE.