Section: 7.1 Network Function Service Framework 7.1.1 General
Content: Service Framework functionalities include e.g. service registration/de-registration, consumer authorization, service discovery, and inter service communication, which include selection and message passing. Four communication options are listed in Annex E and can all co-exist within one and the same network. An NF service is one type of capability exposed by an NF (NF Service Producer) to other authorized NF (NF Service Consumer) through a service-based interface. A Network Function may expose one or more NF services. Following are criteria for specifying NF services: - NF services are derived from the system procedures that describe end-to-end functionality, where applicable (see TS 23.502[ Procedures for the 5G System (5GS) ]  [3], Annex B drafting rules). Services may also be defined based on information flows from other 3GPP specifications. - System procedures can be described by a sequence of NF service invocations. NF services may communicate directly between NF Service consumers and NF Service Producers, or indirectly via an SCP. Direct and Indirect Communication are illustrated in Figure 7.1.1-1. For more information, see Annex E and clauses 6.3.1 and 7.1.2. Whether a NF Service Consumer (e.g. in the case of requests or subscriptions) or NF Service Producer (e.g. in the case of notifications) uses Direct Communication or Indirect Communication by using an SCP is based on the local configuration of the NF Service Consumer/NF Service Producer. An NF may not use SCP for all its communication based on the local configuration. NOTE: The SCP can be deployed in a distributed manner. In Direct Communication, the NF Service consumer performs discovery of the target NF Service producer by local configuration or via NRF. The NF Service consumer communicates with the target NF Service producer directly. In Indirect Communication, the NF Service consumer communicates with the target NF Service producer via a SCP. The NF Service consumer may be configured to perform discovery of the target NF Service producer directly, or delegate the discovery of the target NF Service Producer to the SCP used for Indirect Communication. In the latter case, the SCP uses the parameters provided by NF Service consumer to perform discovery and/or selection of the target NF Service producer. The SCP address may be locally configured in NF Service consumer. Figure 7.1.1-1: NF/NF service inter communication