e standard meanings; these messages are the HTTP methods. Client/Server Identification of resources: Resources (documents, files, images) associated with a network service are uniquely addressed Cacheable Manipulation of resources based on representation Stateless Resources can be manipulated by a client through a standard set of operations (HTTP methods) Layered System Self descriptive messages Messages must contain all the relevant information Uniform required by a Server to fulfill the request Interface Figure 3.9 - Uniform interface - REST in 5G NFs Building Blocks - Cloud Native Infrastructure The aforementioned methods to manipulate resources are based on HTTP/HTTP2 and are as follows: POST: This message requests the server to create a new resource GET: This message retrieves the resource addressed by the URL within the request PUT: This replaces the resource addressed by the Universal Resource Identifier (URI) with the payload of the request PATCH: This updates the resource addressed by the URI and does not replace the content entirely DELETE: This method deletes the resource addressed by the URI in the message The POST, GET, PUT, PATCH, and DELETE methods are used extensively between 5G NFs to request and provide services to each other. REST in 5G In this section, we will learn about the applicability of REST in 5G, and how all the various concepts that we have gone through in the previous sections come together in a 5G system. Figure 3.10 represents some of the RESTful interfaces in a 5G system: NAUSF NNSSF Figure 3.10 - RESTful SBIs in 5G NFs We explore the details of each of them and understand the services provided to and consumed by each of these NFs. We will also understand the role of each of these services and how they contribute to the functionality of the network function as a whole. REST in 5G AMF services The following is a list of services offered by the AMF per 3GPP Release 16, 29.518; note that each service has a name associated with it and can have one or more service operations. These com