Core Networks
Core networks cover the cloud-native mobile core that anchors subscriber sessions and enforces policy. The exam tests the roles of AMF, SMF, UPF, NRF, UDM, PCF, and AUSF, and how Nokia Cloud Packet Core and Cloud Mobility Manager implement control and user plane separation.
Core functions and interfaces
The AMF handles access and mobility signaling; the SMF manages PDU sessions; the UPF forwards user traffic and enforces QoS. The NRF supports service discovery, the UDM holds subscription data, the PCF provides policy, and the AUSF handles authentication. N2 connects the RAN to the AMF, N3 carries user traffic to the UPF, N4 separates SMF control from UPF forwarding, and N6 connects the UPF to data networks. Cloud-native design uses stateless services, service-based interfaces, and horizontal scaling.
Rules to apply
- The AMF does not carry user data; the UPF does.
- SMF selects the UPF using DNN, S-NSSAI, location, load, and policy, not a fixed table alone.
- A PDU session can contain multiple QoS flows; the UPF enforces their treatment.
- S-NSSAI identifies a slice; DNN identifies a data network. They are related but not interchangeable.
- Control-plane and user-plane scaling are independent.
Worked example
A subscriber attaches through a gNB. The AMF authenticates the subscriber with AUSF and UDM, then selects an SMF for the requested DNN and S-NSSAI. The SMF selects a UPF near the subscriber's location and with available capacity, then installs N4 rules for QoS flow treatment. The UPF anchors the PDU session and forwards traffic to the data network over N6. The reasoning: each function has a distinct role, and selection considers policy and load, not only static configuration.
Traps that cost marks
Assuming the AMF forwards user packets; treating DNN and S-NSSAI as the same identifier; selecting a UPF without considering location or load; and forgetting that QoS is enforced in the UPF, not the SMF.