One of the new features of 5GC is the introduction of Service Based Interfaces (SBI) which is part of 5GC’s Service Based Architecture (SBA).

Let’s start with the description from the specs:

3GPP TS 23.501 [3] defines the 5G System Architecture as a Service Based Architecture, i.e. a system architecture in which the system functionality is achieved by a set of NFs providing services to other authorized NFs to access their services.

3GPP TS 29.500 – 4.1 NF Services

For that we have two key concepts, service discovery, and service consumption

Services Consumer / Producers

That’s some nice words, but let’s break down what this actually means, for starters, let’s talk about services.

In previous generations of core network we had interfaces instead of services. Interfaces were the reference point between two network elements, describing how the two would talk. The interfaces were the protocols the two interfaces used to communicate.

For example, in EPC / LTE S6a is the interface between the MME and the HSS, S5 is the interface between the S-GW and P-GW. You could lookup the 3GPP spec for each interface to understand exactly how it works, or decode it in Wireshark to see it in action.

5GC moves from interfaces to services. Interfaces are strictly between two network elements, the S6a interface is only used between the MME and the HSS, while a service is designed to be reusable.

This means the Service Based Interface N5g-eir can be used by the AMF, but it could equally be used by anyone else who wants access to that information.

3GPP defines the service in the form of service producer (The EIR produces the N5g-eir service) and the service consumer (The client connecting to the N5g-eir service), but doens’t restrict which network elements can

This gets away from the soup of interfaces available, and instead just defines the services being offered, rather than locking the

“service consumers” (which can be thought of clients in a client/server model) can discover “service producers” (like servers in a client/server model).

Our AMF, which acts as a “service consumer” consuming services from the UDM/UDR and SMF.

Service Discovery – Automated Discovery of NF Services

Service-Based Architecture enables 5G Core Network Function service discovery.

In simple terms, this means rather that your MME being told about your SGW, the nodes all talk to a “Network Repository Function” that returns a list of available nodes.

I’ve written a full blog post on the NRF that explains the concepts.