6.3.14 NEF Discovery

The NF consumers may utilize the NRF to discover NEF instance(s) unless NEF information is available by other means, e.g. locally configured in NF consumers. The NRF provides NF profile(s) of NEF instance(s) to the NF consumers.

The IP address(es)/port(s) of the NEF or L-NEF may be locally configured in the AF, or the AF may discover the FQDN or IP address(es)/port(s) of the NEF/L-NEF by performing a DNS query using the External Identifier of an individual UE or using the External Group Identifier of a group of UEs or using EDNS Client Subnet, or, if the AF is trusted by the operator, the AF may utilize the NRF to discover the FQDN or IP address(es)/port(s) of the NEF or L-NEF.

NOTE 1: When the AF discovers the FQDN or IP address(es)/port(s) of the NEF/L-NEF by performing a DNS query, the AF can add in its DNS request an EDNS Client Subnet option in order to help the DNS determine a local NEF directly. The use of a DNS query for the selection of a L-NEF is only supported for AF and not internal network functions.

NOTE 2: The EDNS Client Subnet may be derived by the AF based on factors that are considered for NEF selection. Whether and which factors are considered for NEF/L-NEF selection may depend on whether the AF performs an initial NEF discovery or a NEF discovery due to L-PSA relocation.

NOTE 3: The NEF discovery and selection procedures described in this clause are intended to be applied by NF consumers deployed within the operator's domain.

NOTE 4: The NEF supporting the capabilities can be configured in the AF or discovered by AF with the assistance of NRF.

The following factors may be considered for NEF selection:

• S-NSSAI(s);
• S-NSSAI and DNN corresponding to an untrusted AF;
• Event ID(s) supported by an AF (see clause 6.2.6, clause 6.2.2.3 of TS 23.288 [86] and clause 5.2.19 of TS 23.502 [3]);
• AF Instance ID, Application Identifier;
• External Identifier, External Group Identifier, or domain name;
• A request for local NEF selection;
• Location (see locality in clause 6.1.6.2.2 of TS 29.510 [58]);
• (for local NEF selection) List of supported TAI;
• (for local NEF selection) List of supported DNAI;
• Capability of NEF to support UAS NF functionality for UUAA procedures;
• Capability of NEF to support Multi-member AF session with required QoS for a set of UEs identified by a list of UE addresses;
• Capability of NEF to support member UE selection assistance functionality.

Local NEF instance(s) can be deployed close to UE access. For local NEF selection, the location of the local NEF instance (e.g. geographical location, data centre) may be used in conjunction with the location of L-PSA UPF or AF.

In the case of Vertical Federated Learning (VFL), the NF consumer (e.g. NWDAF) may also consider other factors supported by NEF, such as untrusted AF's VFL capability information per Analytics ID and other related parameters as defined in clause 5.5 of TS 23.288 [50].