Understanding the Functional Building Blocks of the 5G Core Network

5G core is the central part of the 5G network. It controls all the interfaces, protocols, and services that allow the system to work as intended. When developing 5G cores, companies must adhere to the 3GPP standards, which prescribe what these systems should look like.

Going from 4G to 5G core represents a major shift for any business. With modern telecommunication solutions, companies are able to cater to a much larger audience. Furthermore, 5G core allows the use of advanced technological solutions such as IoT, autonomous vehicles, and smart cities. 

Each core consists of numerous smaller parts, which have a high level of autonomy (otherwise referred to as network functions or NFs). We use these NFs for data management, authentication, policy management, quality of service, and other purposes. 

5G Network Architecture Basics

Each network function within 5G is categorized based on services, resulting in a methodology we refer to as SBA (Service-Based Architecture). Every NF fulfills a specific role and is vital to the overall functionality of the entire network. They are interconnected in a larger system, communicating with each other to execute certain tasks. 

For example, every network function within 5G can register and subscribe to other network functions’ services. NFs communicate with each other by relying on the HTTP/2 protocol. 

One of the main goals of 5G tech developers was to reduce dependencies between the core network and the access network. They managed to do so by introducing a unified access-agnostic core that shares an interface between the core and the access network with diverse non-3GPP and 3GPP access types. 

Understanding NFs Within 5G Core Network

As mentioned, 5G core relies on numerous network functions. Each of them has a specific purpose and can communicate with other NFs through well-defined interfaces. This makes 5G networks much more flexible than the past iterations of telecommunication networks.

Here are some of the main NFs you should know about:

SMF (Session Management Function) 

SMF is one of the vital components of the network, basically managing all the sessions for UE (User Equipment). It relies on protocols and interfaces to fulfil its role, among others, Nsmf (Network Function-specific Service-based Interface) and PFCP (Packet Forwarding Control Protocol).

The Session Management Function is in constant communication with other functions, including AMF (Access and Mobility Management Function), PCF, and UPF. It ensures unobstructed transfer of data within the network. 

SMF is also vital for resource allocation, handling of QoS (Quality of Service) parameters, routing info, changing session data, and policy enforcement. The Session Management Function provides a certain degree of control plane functionality. In particular, it allows the use of PGW-C and SGW-C. 

UPF (User Plane Function) 

Another essential component within the 5G core network, UPF, is responsible for handling all user data during its transfer. The User Plane Function’s main role is to connect the data network with the RAN (Radio Access Network). 

Basically, it extracts data from the Radio Access Network and uses it to perform all sorts of tasks. For example, UPF is responsible for packet processing and inspection, traffic routing, and quality of service enforcement. The NF shifts the data plane toward the network edge, which minimizes latencies while enhancing data rates.

UPF serves as a combination of P-GW and traffic transport function. It manages various interfaces, for example, those between UPF and RAN, between two UPFs, between UPF and SMF, and between UPF and Data Network (DN). 

AMF (Access and Mobility Function) 

The main role of AMF is to handle mobility and connections. The NF manages authentication, session, and policy control data from a device and transfers it to SMF, PCF, and other network functions that require the information. 

AMF is not a new function. A similar component was present in 4G, known as the Mobility Management Entity. Although MME’s function has been altered in 5G core, the AMF still shares some similarities with it. Specifically, both MME and AMF prioritize mobility and connection management. 

We also have to mention that AMF is vital when sending SMS, as it retrieves subscription info. The NF is able to identify a network slice by relying on S-NSSAI, or Single Network Slice Selection Assistance Information. By relying on AMF, the 5G core network is able to streamline connection, mobility, and registration of user equipment. 

NEF (Network Exposure Function) 

NEF allows network operators to expose network interfaces and functionality with high safety and reliability. It provides users with granular access by bridging the gap between external applications and the 5G core network. NEF also facilitates AF (Application Functions), which ensures safe data transfer to a 3GPP network.

By allowing external applications to access network capabilities, NEF helps businesses fulfil their goals. It ensures seamless connection between different requirements and network capabilities, enhancing resource usage and allocation. All in all, NEF will enhance the experience for all users across the board. 

PCF (Policy Control Function) 

PCF gives operators a framework for introducing different policies. After creating said policies, they are utilized by other control plane NFs. For example, you can introduce rules regarding usage monitoring, QoS, network slicing, subscriber and application management, and so on.

Similar to PCRF (Policy and Charging Rules Function) in 4G, PCF in 5G core handles the role of policy decision point. Similar to other NFs, it is able to communicate with other components such as UDM, SMF, and AMF. 

Last Thoughts 

5G core network relies on a complex yet fairly autonomous architecture to deliver a premium experience to users. These telecommunication systems are ideal for modern companies that use various technologies, including autonomous vehicles, robots, and the Internet of Things.

5G networks’ functions, referred to as NFs, are able to communicate with each other, thus relaying vital information. Each of them fulfils a particular role while also serving as a part of a larger system. The architecture enables network slicing and containerization, partitioning physical infrastructure into distinct parts for various use cases.