Section: 7.1.5 Network Function and Network Function Service registration and de-registration
Content: For the NRF to properly maintain the information of available NF instances and their supported services, each NF instance informs the NRF of the list of NF services that it supports. NOTE: The NF informs the appropriate NRF based on configuration. The NF instance may make this information available to NRF when the NF instance becomes operative for the first time (registration operation) or upon individual NF service instance activation/de-activation within the NF instance (update operation) e.g. triggered after a scaling operation. The NF instance while registering the list of NF services it supports, for each NF service, may provide a notification endpoint information for each type of notification service that the NF service is prepared to consume, to the NRF during the NF instance registration. The NF instance may also update or delete the NF service related parameters (e.g. to delete the notification endpoint information). Alternatively, another authorised entity (such as an OA&M function) may inform the NRF on behalf of an NF instance triggered by an NF service instance lifecycle event (register or de-registration operation depending on instance instantiation, termination, activation, or de-activation). Registration with the NRF includes capacity and configuration information at time of instantiation. The NF instance may also de-registers from the NRF when it is about to gracefully shut down or disconnect from the network in a controlled way. If an NF instance become unavailable or unreachable due to unplanned errors (e.g. NF crashes or there are network issues), an authorised entity shall de-register the NF instance with the NRF.