Service-based architecture — The core as a set of services, not a set of nodes

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The core network

Where it sits

Sits atLevel 2 of the hierarchy · The core network · explained
Also writtenSBA
Learn firstNetwork function — 2 concepts in the full chain, see the paths
UnlocksSBI · NEF
Primary clauseTS 23.501 §7.1
Used inref-core 5 · ref-session 4 · index 1
Scanned from the notes at page load and joined with terms.json; nothing on this card is typed by hand.

What it is

What it is. The description of the 5G core as a set of services offered and consumed, rather than nodes joined by interfaces. TS 23.501 §7.1. A function that offers a service is a NF service producer; one that calls it is a NF service consumer; and the same function is routinely both.

The three moves that make it work:

  1. One interface for everybody. Instead of N-something per pair of nodes, there is a single service-based interface — HTTP/2 with JSON bodies — and every function speaks it. Adding a consumer costs nothing.
  2. Producers register; consumers discover. A function registers its NF profile with the NRF and consumers ask the NRF who can serve them (NF service). Nothing is configured with anyone else's address.
  3. The service, not the function, is the unit. A consumer asks for a service (Namf_Communication, Nsmf_PDUSession, Nudm_SDM), which is why the naming in the specification is N<function>_<service> rather than a link name.

Why this is the enabler and not the decoration. Consider adding network slicing to a node-based core. Each slice needs its own set of control-plane nodes, and every node in a slice must be told the addresses of the others — the configuration cost grows with slices × interfaces. Under the SBA, a new slice is a new set of instances that register themselves and are found by discovery, and the NSSF only has to answer which slice, not where anything is.

The same argument explains NEF: once every internal capability is already an HTTP service, exposing a curated subset outward is a matter of putting one function in front of them, not of inventing an external protocol.

What it is not. The SBA covers the control plane only. The user plane is a GTP-U tunnel between the base station and the UPF, and the N4 interface that controls the UPF is PFCP, not HTTP. Packets do not travel over REST, and the CP/UP split is what keeps that distinction clean.

Read on

This concept is read as part of one argument in ref-core, alongside the rest of its group.

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Before this concept, the hierarchy says to learn the following — the full chain, in order:

To understand Service-based architecture (level 2) you first need 2 other concepts. Read them in this order — everything on one line can be read in any order, but no line before the one above it:
Level Learn these
0 5G Core
1 Network function
Immediately before Service-based architecture: Network function.
Keep going — where this sits on the route
◀CP/UP splitstep 16 · level 2
Step 17 of 118level 2 · The core network
NSSFstep 18 · level 2▶
Level 2 → 3 · this unlocks
SBI · NEF
↳ all 9 concepts at level 3 · level 2 in full · the whole route
The route is every concept in the folder ordered by level, so nothing here needs anything after it. Computed at page load from terms.json; the same numbering as the route page.
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