Feature Description
The SMF follows a priority order for different NF selection options. The SMF prioritizes the NF discovered from the NRF over the local configuration. The SMF uses the locally configured NFs 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 through the profile nf-pair parameter. For more details, see Configuring Locality for NF Types in the NRF Selection per Peer NF Type 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:
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The NF discovery response cache has no matching entries.
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The NF discovery response cache has matching entries, but the validity has expired.