5G Core Network Architecture Explained: APIs, Service-Based Functions, and Interfaces
Understanding the 5G Core Network Architecture: APIs, Service-Based Functions, and Interfaces
The 5G Core Network (5GC) marks a significant shift from traditional telecom setups, aimed at facilitating cloud-native, service-oriented, and API-driven operations. In contrast to the 4G EPC (Evolved Packet Core), 5G Core introduces a Service-Based Architecture (SBA) that supports flexible scaling, interoperability among different vendors, and the integration of modern technologies like edge computing and network slicing.
The accompanying image gives a visual overview of this architecture, illustrating how control-plane and user-plane functions interact through APIs (HTTP/JSON). Each network function communicates via standardized interfaces, promoting modularity and flexibility.
In this piece, we’ll unpack the key network functions, explore how APIs enhance interoperability, and highlight why this architecture is vital for the future of telecommunications.
- What is the 5G Service-Based Architecture (SBA)?
The Service-Based Architecture (SBA) in 5G is a cloud-native model where various network functions (NFs) offer their services through APIs. These APIs typically use HTTP/2 and JSON, enabling telecom networks to leverage similar web-scale tools and technologies that drive contemporary cloud applications.
Some standout features of SBA include:
API-driven: Communication happens entirely through APIs.
Modularity: Each function works independently but integrates well with others.
Scalability: Functions can scale out in cloud environments.
Interoperability: Open APIs enable support for multi-vendor ecosystems.
- Separation of Control Plane and User Plane
A key characteristic of the 5G Core is the Control and User Plane Separation (CUPS).
Control Plane (CP):
Manages signaling, authentication, session management, and policies.
Includes important functions like AMF, SMF, PCF, UDM, AUSF, NRF, NSSF.
User Plane (UP):
Handles the actual data transfer between user equipment (UE) and the internet or applications.
Main function: UPF (User Plane Function).
This separation permits independent scaling, meaning control functions can grow to handle signaling-heavy situations while user-plane functions can expand for data-heavy tasks.
Key Network Functions in 5G Core
The diagram showcases essential network functions (NFs):
Access and Mobility Management Function (AMF)
Takes care of registration, mobility, and connection management.
Connects with UE through the N1 interface and interacts with the RAN over N2.
Directs session requests to the SMF.
Session Management Function (SMF)
Manages session establishment, modification, and release.
Assigns IP addresses to UEs.
Selects and oversees UPFs.
User Plane Function (UPF)
Central point for data forwarding.
Links the RAN to Data Networks (DN), like the internet, private enterprise networks, or MEC platforms.
Operates on the N3, N6, and N9 interfaces.
Policy Control Function (PCF)
Sets policy rules regarding quality of service (QoS), traffic routing, and billing.
Similar to the PCRF found in LTE, but improved for 5G.
Authentication Server Function (AUSF)
Handles subscriber authentication in partnership with UDM.
Secures network access for UEs.
Unified Data Management (UDM)
Responsible for storing and managing subscriber profiles.
Provides authentication credentials and subscription data.
Network Slice Selection Function (NSSF)
Allocates users to suitable network slices based on their service requirements.
Vital for implementing network slicing in 5G.
Network Repository Function (NRF)
Keeps a record of available network functions and services.
Facilitates service discovery, enabling NFs to dynamically find and communicate with one another.
Network Exposure Function (NEF)
Offers secure access to network services for external applications.
Fosters API-driven innovation by making it easier for third-party developers and enterprises to integrate.
Application Function (AF)
Connects with the PCF for application-specific policy control.
For instance, it can be used for video optimization, gaming, or enterprise applications.
Interfaces in 5G Core
The diagram outlines several reference points between functions:
N1: Between UE and AMF (signaling).
N2: Between AMF and RAN.
N3: Between RAN and UPF (user data).
N4: Between SMF and UPF.
N6: Between UPF and external Data Networks (DN).
N9: Between UPFs (inter-UPF communication).
These interfaces ensure distinct responsibilities while allowing for flexible deployment in cloud-native settings.
- Role of APIs (HTTP/JSON) in 5G
5G takes a different approach compared to older telecom protocols like Diameter or SS7, embracing HTTP/2 and JSON-based APIs.
Benefits include:
Cloud-native alignment: Utilizes widely accepted internet protocols.
Simplified integration: Third-party apps and services can interact directly with the network.
Service discovery: Thanks to the NRF, functions can dynamically discover and link via APIs.
Security: APIs come with TLS encryption and authentication options.
This change is pivotal for making 5G a platform for innovation, making it easier for industries like IoT, smart cities, and self-driving cars to connect seamlessly.
Benefits of 5G SBA
The service-oriented model driven by APIs offers several significant benefits:
Flexibility: Functions can be deployed centrally, at the network edge, or in hybrid configurations.
Vendor Interoperability: Promotes a diverse ecosystem of vendors.
Speedier innovation: APIs enable quicker rollout of new services.
Scalable Network Slicing: Allows for on-demand slices tailored for industries (like healthcare, automotive, AR/VR).
Cloud compatibility: Functions operate as containers or microservices, which supports DevOps and CI/CD practices.
Challenges in SBA Deployment
Even with its strengths, SBA poses some challenges for operators:
API Management: Requires proper API governance to prevent complications.
Security Risks: Exposing APIs might enlarge the attack surface.
Performance Overhead: Using HTTP/JSON could introduce latency compared to traditional telecom signaling.
Vendor Coordination: Multi-vendor setups need strict adherence to 3GPP standards.
Use Cases Enabled by 5G Core SBA
The adaptability of 5G Core empowers operators to provide a range of applications:
Enhanced Mobile Broadband (eMBB) – Faster internet connections and improved user experiences.
Ultra-Reliable Low Latency Communication (URLLC) – Critical services like self-driving cars and remote surgeries.
Massive Machine-Type Communication (mMTC) – Connecting billions of IoT devices.
Private 5G Networks – Businesses utilizing slices for dedicated services.
Edge Computing – Low-latency applications with UPFs located close to users.
Conclusion
The 5G Core Service-Based Architecture (SBA) signifies a major evolution in telecom networks. Adopting HTTP/JSON APIs, cloud-native strategies, and modular functions gives operators remarkable flexibility, scalability, and potential for innovation.
Functions such as AMF, SMF, and UPF are crucial for session management and transferring user data.
Supporting functions like PCF, AUSF, UDM, NSSF, NRF, and NEF ensure security, policy enforcement, and exposure of services.
APIs facilitate seamless integration with external applications, driving digital transformation across various industries.