O on. In the next chapter, we will discuss the building blocks of 5G, which is the cloud-native infrastructure. We will compare and contrast the 4G and 5G network design principles. Building Blocks - Cloud Native Infrastructure In this chapter, we will learn about the infrastructure building blocks of 5G. We will cover the evolution of telecom infrastructure from legacy networks (3G-4G) to 5G networks. We will discuss in detail producer-consumer models, cloud-native infrastructures, REST principles, and service-based interfaces in 5G. Understanding these topics will help us understand the real transformation that 5G technology is about to bring to the world of telecom applications and infrastructure. By the end of this chapter, we will be able to understand the fundamentals of telecom infrastructure and its evolution. We will also be delving into details about service-based infrastructure and how it applies to 5G Network Functions (NFs). In addition to this, we will cover the services offered by each network function and who consumes them. This will be more of an implementation view of the functions, roles, and responsibilities of the NFs we discussed earlier in Chapter 2, in the context of the services offered and consumed. In this chapter, we'll cover the following main topics: The evolution of telecom infrastructure Cloud-native infrastructure and applications Service-based architecture What is REST? REST in 5G The evolution of telecom infrastructure Over the past few decades, telecom infrastructure has been built primarily on proprietary appliance- based hardware. The network elements in 3G and 4G were built using monolithic software principles and were not designed for distributed functions. It was also not easy to scale these network elements or out without adding or removing bulky and space/power-hogging custom appliances. Building Blocks - Cloud Native Infrastructure In many cases, the service provider themselves would request only a fraction of the capacity of the appliance for, say, adding a small perce