SBI
Service-Based Interface: the API interface exposed by each 5GC network function, using HTTP/2 with JSON payloads for service registration, discovery, and invocation.
SBI is the architectural style of the 5G core: instead of fixed point-to-point interfaces between named nodes, each network function exposes services as APIs that any authorised consumer can call. A function registers its services with the NRF (the repository), other functions discover it there, and they invoke it over HTTP/2 with JSON. So rather than "the MME talks to the HSS over S6a with these Diameter messages," you have "the AMF consumes the UDM's subscriber-data service via its API."
The payoff is modularity and cloud-native operation. Services can be deployed, scaled and updated more independently, and adding a consumer doesn't require a brand-new interface — it just calls an existing service. Naming reflects this: interfaces carry service names like Namf, Nudm, Nsmf rather than the old letter-number labels. The trade-offs are the ones any API platform faces — discovery, authorization between services (via OAuth2 tokens), and securing the calls — which is why the NRF and the SEPP matter so much in this model.
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