The 5GC represents the heart of the 5G network and has evolved towards a service based architectural system. A service based architecture enables components within a network to work together, independent of vendors, products and technologies. The service based framework has also triggered virtualisation and softwarisation within the 5GC which allows the network to meet the varied requirements of the various 5G use cases. The evolution within the 5GC has also resulted in the separation of the data and control plane. This chapter introduces the reader to the evolution and innovative concepts implemented within the 5GC.
5.1 Network Slicing
The three use cases of 5G have different stringent requirements e.g. latency, ultra-high bandwidth, dense traffic etc. It therefore becomes a challenge to support all these services within the same physical infrastructure .
Furthermore, the network has to be able to react to the demand of the users regardless of their geographic locations.
To address these challenges, end to end Network Slicing, has been introduced. A network slice is simply an end to end logical network running on a shared physical infrastructure as depicted in Fig. 5.1 above.
In essence, the network is sliced into multiple virtual networks to support different radio access technologies or services with different requirements transported within the same physical infrastructure e.g. a slice would be developed for low latency applications while another slice is developed for high bandwidth applications. These slices are different and would be transported within the same physical infrastructure. This is clearly illustrated in Fig. 5.1 above [14, 15, 16, 17].
Network slices can further be customized depending on the requirements of the vertical or even the operators. For example, an automated car may require high bandwidth for its infotainment and low latency for assisted driving; these services could be delivered on different slices packaged together as a business bundle [15, 16].
Furthermore, a vertical requiring two or more services may request for a unique hierarchy for delivering these services. Thus, network slicing offers the opportunity to meet personalized requests .
Slicing can further be categorized as vertical or horizontal. Vertical slicing refers to the development of slices to serve the different requirements of the verticals, as illustrated above [16, 18].
Whereas, horizontal slicing implies developing similar slices to meet the needs of different machines or users with similar requirements. For example, a horizontal slice could be developed to simultaneously serve the needs of a consumer in a smart home and sensors within a smart industry, since they have the same requirements .
5.2 Network Function Virtualization
In order to facilitate the smooth transport of the virtual slices within the network and control slices on the fly (based on application requirements), Network Function Virtualization (NFV) has been introduced. The Service based architectural framework of the core has also facilitated the use of NFV which has seen architectural elements now defined in terms of network functions rather than actual physical network entities. The recent advancement in general purpose technology, cloud computing and software defined networks  has also triggered the use of NFV.
In simple terms, NFV refers to the virtualization of network functions like routers, firewalls, evolved packet core etc.; these network functions now run on virtual machines within a cloud infrastructure, as depicted in Fig. 5.2. It thus represents a shift from hardware to software within the network and leads to a reduction in capital expenditure [17, 18].
NFV thus enables the network to become programmable, agile and dynamic and reduces the costs associated with purchasing hardware for network entities. NFV would also enable the network to be able to react to the demand of the users, which is a key necessity for 5G applications [17, 18].
5.3 Software Defined Networking
In the previous chapter, it was pointed out that 5G would most likely be represented by a large heterogeneous network. And as a network becomes bigger, agility, flexibility, control and management etc. become very difficult. Such network therefore require some form of remote control from a distance via logical interfaces. In order to overcome these challenges, Software Defined Networking (SDN), an intelligent network architecture, is introduced for use in 5G networks .
SDN simply replaces traditional hardware with programmable software services and separates the control plane from the data plane. It allows for a simplified network management and introduces flexibility within the network. SDN also allows for the dynamic reconfiguration of the network and thereby give users the perception of infinite capacity for their applications, as depicted in Fig. 5.3 [17, 18, 19, 20].
5.4 Control User Plane Separation (CUPS)
The service based architecture of the core has accelerated softwarisation within the network, and this has triggered the separation of the gateways in the EPC of the 4G network into a control plane and user plane in order to meet the low latency requirement for certain 5G use cases.
The control plane refers to a forwarding plane for exchanging signalling information needed to support the operations of the service delivered to the user. The user plane, on the other hand, represents the forwarding path for the user’s data (as depicted in Fig. 5.4) and supports other functionalities like charging, policy enforcement and a wide range of network capabilities.
With the CUPS technique (greatly facilitated by virtualisation and softwarisation), one could easily deploy a control plane within a centralized location whereas a user plane is deployed closer to the user. This has also accelerated the use of the MEC technique discussed in the next section.
5.5 Mobile Edge Computing
The softwarisation of the network has enabled the introduction of newer technologies like Mobile Edge Computing (MEC). This simply means bringing the cloud/IT services closer to the edge of the network or the users, as depicted below in Fig. 5.5. Here, the contents are stored on the MEC Server closer to the user. Anytime a user requires a service, it is served with little delay because of the close proximity to the MEC Server. This therefore gives the user a perception of infinite capacity.
MEC reduces latency, improves the quality of experience, allow for contextualized services and efficient use of resources [15, 17].
The 5GC has been designed as a service based architectural network which would allow logical entities within the virtual network to communicate via protocols. This has greatly aided softwarisation and virtualization within the network. The virtualization and softwarisation of the core has encouraged the separation of control plane from the user plane and greatly facilitated the use of techniques like Network slicing, NFV, SDN, MEC, Artificial Intelligence (AI), Machine Learning (ML) and Data Analytics etc. which all serve to meet the varied requirements of 5G applications and allow for the network to be flexible, agile, dynamic, reconfigurable and able to react and respond to the demands of the users/verticals on the fly.