5.21.3.3 Reliability of NF instances within the same NF Set

The NF producer instance is the NF instance which host the NF Service Producer. When the NF producer instance is not available, another NF producer instance within the same NF Set is selected.

For Direct Communication mode, the NF Service consumer may subscribe to status change notifications of NF instance from the NRF. If the NF Service consumer is notified by the NRF or detects by itself (e.g. request is not responded) that the NF producer instance is not available anymore, another available NF producer instance within the same NF Set is selected by the NF Service consumer.

For Indirect Communication mode, the SCP or NF Service consumer may subscribe to status change notifications of NF instance from the NRF and select another NF producer instance within the same NF Set if the original NF producer instance serving the UE is not available anymore.

For both Direct Communication mode, the NF, or Indirect Communication mode, the NF or SCP may select another NF producer instance within the same NF Set based on notification of subscription of signalling storm analytics from NWDAF.

NOTE: It is up to the implementation on how the SCP knows a NF producer instance is not available anymore.