SCP Interface

The Service Communication Proxy (SCP) is the routing control point that mediates all signaling and Control Plane messages in the network core. SCP is responsible for optimizing routing of NF discovery requests to the Network Repository Function (NRF), load balancing, traffic prioritization, and message management.

Communication Models for NF and NF Services Interaction

For a 3GPP 5GC enhanced SBA (eSBA) network, 3GPP defines four communication models that NF and NF services (Consumer NF and a Producer NF) can use to interact which each other. These communication models are Model A, B, C, and D.

Note

SMF supports Models A, B, and D.

The following table lists the communication models, their usage, and how they relate to the usage of an SCP.

Communication Models for NF and NF Services Interaction

Communication Between Consumer NF and Producer NF

Service Discovery and Request Routing

Communication Model

Direct communication

No NRF or SCP; direct routing

A

Discovery using NRF services, no SCP; direct routing

B

Indirect communication

Discovery using NRF services; selection for specific instance from the set can be delegated to SCP. Routing is done through SCP.

C

Discovery and associated selection delegated to an SCP using discovery and selection parameters in service request. Routing is done through SCP.

D

Communication Models for NF and NF Services Interaction

In Model A, there is a direct communication without the NRF interaction. No NRF or SCP is used. The consumers are configured with the producer NF profiles and directly communicate with the producer of their choice.

In Model B, there is a direct communication with the NRF interaction. Consumers perform discovery by querying the NRF. Based on the discovery result, the consumer does the selection. The consumer sends the request to the selected producer.

In Model C, there is an indirect communication without the delegated discovery. Consumers perform discovery by querying the NRF. Based on discovery result, the consumer does the selection of an NF Set or a specific NF instance of NF set. The consumer sends the request to the SCP containing the address of the selected service producer pointing to a NF service instance or a set of NF service instances. The SCP routes the request to the selected NF service producer instance.

In Model D, there is an indirect communication with the delegated discovery. Consumers do not perform any discovery or selection. The consumer adds the required discovery and selection parameters to find an appropriate producer to the service request. The SCP uses the request address and the discovery and selection parameters in the request message to route the request to a appropriate producer instance. The SCP can perform discovery with an NRF and obtain a discovery result.