Complete Guide to 5G Architecture: Grasping the Core, Interfaces, and Data Flow
5G is a game changer when it comes to network design, especially compared to 4G LTE. Instead of sticking to a single, large EPC, it adopts a Service-Based Architecture (SBA), which is modular, adaptable, and suited for the cloud. Check out the 5G Architecture diagram we’ve uploaded for a clear visual of how the 5G elements connect—from User Equipment (UE) to the RAN and through the 5G Core (5GC).
In this detailed overview, we’ll go through each block in the diagram, explain what each part does, describe the interfaces (N1, N2, N3, N4, N6, N9), and give you a solid understanding of how data and control signals flow through the network.
This piece is tailored for telecom experts, 5G engineers, and anyone with a keen interest in getting to grips with the structure of modern mobile networks.
- High-Level Overview of the 5G Architecture (From the Diagram)
The diagram is split into three main layers:
A. User Layer
UE1 and UE2
B. Access Layer
(R)AN (which could be gNB or NG-RAN)
Backhaul network / Datacenter (DC) clouds
C. 5G Core (5GC)
This includes:
AMF
SMF
Multiple UPFs
AF and DN
SBA Network Functions (AUSF, NSSF, NEF, NRF, PCF, NWDAF)
This layered structure reflects the modular and cloud-native approach of 5G networks.
- User Equipment (UE1, UE2)
The UEs connect to the 5G Radio Access Network ((R)AN) using the N1 interface.
Key roles of UEs include:
Handling registration and authentication
Sending requests to establish PDU sessions
Managing user-plane traffic for sending/receiving data
Making network slicing requests based on user subscriptions
The UE→RAN connection is where all signaling and data flows begin.
- 5G Radio Access Network – (R)AN
The (R)AN block in the diagram stands for gNB or a distributed NG-RAN system.
Core functions of (R)AN:
Manages radio communication with UEs
Handles RRC (Radio Resource Control)
Schedules uplink and downlink data
Forwards all signaling to AMF (N2)
Sends user data to UPF via N3
This separation between N2 (control) and N3 (user) lines up with the split architecture introduced in LTE and refined in 5G.
- Key 5G Core Functions (AMF, SMF, UPF)
In the center of the diagram, we find the three main 5G Core (5GC) functions:
4.1 Access and Mobility Management Function (AMF)
Connected to the (R)AN through N2, AMF manages only control-plane tasks.
AMF Duties Include:
Handling registration
Overseeing mobility and reachability functions
Terminating NAS signaling
Managing security authentication (via AUSF)
Selecting appropriate SMF for sessions
Controlling paging
AMF acts as the centralized signaling anchor within the 5GC.
4.2 Session Management Function (SMF)
The SMF is responsible for establishing and overseeing PDU sessions.
It communicates with:
AMF (N11 – not explicitly shown but implied)
UPFs (N4 interface)
PCF for policy control
AF for application-level interactions
SMF Duties Include:
Setting up and releasing PDU sessions
Allocating IP addresses
Choosing UPF(s)
Configuring routing rules for UPF
Enforcing policy decisions (from PCF)
SMF serves as the control-plane brain for user traffic paths.
4.3 User Plane Function (UPF)
The diagram portrays multiple UPFs (UPF1, UPF2, UPF3), showcasing the distributed, edge-enabled nature of the 5G data plane.
UPF Duties Include:
Routing and forwarding user data
Steering traffic toward Data Networks (DN)
Enforcing QoS
Detecting and measuring packets
Anchoring mobility
Offloading to edge (via UPF close to MEC servers)
UPF is the core of the 5G data plane, supporting ultra-low latency services.
- Service-Based Architecture Functions (Upper Layer)
At the top of the diagram, the service-based functions interact through SBA APIs (Nausf, Nnssf, Npcf, Nnef, Nnrf, Nnwdaf).
These interfaces are entirely HTTP/2-based and designed to work well in cloud environments.
5.1 AUSF – Authentication Server Function
This function manages the authentication processes for UEs in conjunction with AMF.
5.2 NSSF – Network Slice Selection Function
It ensures that the right slice is assigned based on subscriber profiles and network loads.
5.3 NEF – Network Exposure Function
This function securely exposes 5G capabilities and events to external applications.
5.4 NRF – Network Repository Function
It enables service discovery, allowing 5G functions to:
register themselves
discover one another
Think of it as the directory service for the SBA.
5.5 PCF – Policy Control Function
This provides policy and QoS rules to:
SMF (for managing sessions)
AMF (for access and mobility)
5.6 NWDAF – Network Data Analytics Function
This function supplies analytic insights like:
traffic predictions
load analytics
anomaly detection
optimizing slices
It’s powered by AI/ML-driven analytics to enhance automation.
- Data Networks (DN) & Application Function (AF)
On the right side, the DN represents:
Internet
Enterprise networks
Operator services
Cloud tasks
User traffic makes its way to the DN through N6 from UPF1 or UPF3.
AF (Application Function)
Found near UPF3, the AF interacts with:
SMF
PCF
It’s primarily used for:
MEC applications
optimizing content
handling enterprise service logic
Being close to UPF3 highlights edge computing (MEC) for low-latency applications.
- Key 5G Interfaces (Based on the Diagram)
InterfaceBetweenPurposeN1UE ↔ AMF (via RAN)NAS signalingN2RAN ↔ AMFControl-plane signalingN3RAN ↔ UPFUser-plane dataN4SMF ↔ UPFConfigure forwarding rulesN6UPF ↔ DN/AFData toward external networksN9UPF ↔ UPFInter-UPF routing/branchingSBA InterfacesAMF, SMF, PCF, NRF, NSSF, AUSF, NEF, NWDAFService discovery & policy control
These interfaces facilitate modularity, slicing, and distributed setups.
- Multi-UPF Architecture in the Image
The diagram shows 5G’s ability to deploy UPFs flexibly:
UPF1 – Core UPF
Connects to external DN
Handles general Internet traffic
UPF2 – Intermediate UPF
Linked to UPF1 via N9
Can support routing optimizations
UPF3 – Edge UPF
Situated near local servers or MEC applications
Provides ultra-low-latency computing
This structure is crucial for:
AR/VR
IoT
Autonomous systems
High-bandwidth enterprise setups
- Data Flow in the 5G Diagram
Here’s a simplified flow based on the diagram:
UE connects to (R)AN through N1/N2/N3.
AMF takes care of registration and authentication.
AMF picks SMF (with help from NRF & NSSF).
SMF selects suitable UPF(s).
SMF sets up UPF routing via N4.
User-plane traffic flows straight through: * UE → (R)AN → UPF → DN (via N6).
For edge services, traffic diverts to UPF3 → MEC/Local Server.
Network analytics (NWDAF) optimize everything.
This nicely captures the logical structure laid out in the uploaded diagram.
Conclusion
The uploaded 5G Architecture diagram provides a solid overview of the contemporary 5G Core, showing how modular, cloud-native network functions interact to deliver high bandwidth, low latency, and dynamic network slicing. Getting to grips with AMF, SMF, UPF, SBA functions, and interfaces like N1, N2, N3, N4, N6, and N9 is vital for anyone involved in 5G engineering, deployment, or network design.
The flexible multi-UPF architecture and edge computing options in 5G open the door to innovative real-time services—from immersive XR to automation in industries. As networks progress towards fully virtualized, analytics-driven models, understanding this architecture becomes essential for professionals who are shaping the future of mobile communications.