Feature Description

The SMF follows a priority order for the different NF selection options. It prioritizes the NF discovered from the network repository function (NRF) over the local configuration. The SMF uses the locally configured NFs in the following scenarios:

  • When the NRF endpoints (for discovery) are not configured.

  • When the NF discovery response has no valid NFs.

Depending on the deployment, the preferred server and geo locality server are configured for each of the NFs. The general rule is to select NFs in the preferred server locality followed by NFs in the geo locality server in case the preferred server NFs fail.

For each NF, the SMF provides an option to configure preferred and geo server locality [ profile nf-pair ]. For more details, see Configuring Locality for NF Types in the NRF Interface per Endpoint section.

In addition, each NF discovery response comes with associated validity time. The SMF caches this NF discovery response and uses it to fetch subsequent sessions. The SMF performs the NF discovery in the following conditions:

  • The NF discovery response cache has no matching entries.

  • The NF discovery response cache has matching entries, but the validity has expired.