NRF
Network Repository Function: the 5GC function that maintains a registry of available NF instances and their profiles, enabling service discovery in the SBA.
In the service-based core there's no static wiring telling each function where its peers live. The NRF is the answer to "who's out there and how do I reach them?" Every NF registers a profile with it on startup — type, address, supported services, slices it serves, capacity — and refreshes it with periodic heartbeats. When the SMF needs a UPF or the AMF needs an AUSF, it queries the NRF and gets back a list of suitable candidates to pick from.
That dynamic discovery is what lets you scale functions in and out, or roll new instances, without reconfiguring everybody. It also acts as a trust checkpoint in many deployments, since OAuth2 access tokens for NF-to-NF calls are obtained here. If the NRF is down or its data is stale, discovery breaks and new sessions can stall even when the target NFs are perfectly healthy — so in production it's deployed redundantly.
Frequently asked questions
- Is the NRF like DNS for the 5G core?
- It's a reasonable first analogy — both answer "where is X?" — but the NRF does more. It stores rich NF profiles (services, slices, load, capacity), supports subscribe/notify so functions learn when peers appear or vanish, and often issues the OAuth2 tokens that authorise NF-to-NF calls. DNS just maps names to addresses; the NRF is a live service registry.
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