y cache can be refreshed. Stateless - a REST principle applicable to 5G NFs The request sent by the client to the server must contain all the possible information the server will need to process the request and respond to the client. The server does not need to maintain the state for each client or request, nor does it retain any information that may be present in the client request. Client/Server Cacheable Request Stateless Client Server 3GPP NF Response 3GPP NF Layered Server does not retain any information contained in the System request Uniform Interface Figure 3.7 - Stateless property - REST in 5G NFs This stateless property is adopted by the 5G NFs and enables them to scale easily, without needing to maintain a lot of information on memory or disks. A layered system - a REST principle applicable to 5G NFs The client or service consumer is unaware of whether the service is provided by multiple servers. It is possible that the service requested is provided by multiple systems and an intermediary node is used to load-balance between the servers. What is REST? Client/Server Server 3GPP NF Client is unaware the service is Request Cacheable provided by multiple servers Response Request Stateless Response Client Request Intermediary 3GPP NF Response Layered System Uniform Server Interface 3GPP NF Figure 3.8 - Layered system - REST in 5G NFs The client does not need to know this detail; hence, the client does not need to be configured to contact multiple servers, thus simplifying operations and configurations to a large extent. A uniform interface - a REST principle applicable to 5G NFs All the RESTful interfaces between various NFs have uniform communication methods. Every resource in the producer and consumer is identified by a unique identifier, and this is uniform across all RESTful NFs. In response to a request for a resource, the client receives a representation of that resource. The client can understand the state by inspecting the representation and modify it. Resources are operated on via messages that hav