6.2.6.1 General

The Network Repository Function (NRF) supports the following functionality:

• Supports service discovery of NRF services and their endpoint addresses by the NRF bootstrapping service.
• Supports service discovery function. Receive NF Discovery Request from NF instance or SCP and provides the information of the discovered NF instances (be discovered) to the NF instance or SCP, including the scenario of NF instances residing in a target PLMN to which traffic from certain UEs will be routed as specified in clause 6.44 of TS 22.261 [2]. The NRF may adjust the discovery results based on output of signalling storm analytics as described in TS 23.288 [86].
• Supports P-CSCF discovery (specialized case of AF discovery by SMF).
• Maintains the NF profile of available NF instances and their supported services.
• Maintains SCP profile of available SCP instances.
• Supports SCP discovery by SCP instances.
• Notifies about newly registered/updated/ deregistered NF and SCP instances along with its potential NF services to the subscribed NF service consumer or SCP (NWDAF may use the notification of updates for signalling storm analytics).
• Maintains the health status of NFs and SCP.

In the context of Network Slicing, based on network implementation, multiple NRFs can be deployed at different levels (see clause 5.15.5):

• PLMN level (the NRF is configured with information for the whole PLMN),
• shared-slice level (the NRF is configured with information belonging to a set of Network Slices),
• slice-specific level (the NRF is configured with information belonging to an S-NSSAI).

In the context of roaming, multiple NRFs may be deployed in the different networks (see clause 4.2.4):

• the NRF(s) in the Visited PLMN (known as the vNRF) configured with information for the visited PLMN.
• the NRF(s) in the Home PLMN (known as the hNRF) configured with information for the home PLMN and optionally with information for target PLMN(s) to which traffic from certain UEs will be routed as specified by clause 6.44 of TS 22.261 [2], referenced by the vNRF via the N27 interface. The hNRF may also query a NRF in a target PLMN as specified in clause 4.17.5 of TS 23.502 [3].

NOTE: The NRF in HPLMN interacts with NRF in target PLMN for certain UEs based on SUPI or Routing Indicator, if one of these parameters is included in the query.