Endpoint Address

Description

In the 5G Service Based Architecture (SBA), the Endpoint Address is a critical concept for enabling communication between Network Functions (NFs). An Endpoint Address is an address in the format of an IP address, transport and port information, or a Fully Qualified Domain Name (FQDN), which is used to determine the host/authority part of the target URI. This target URI is used to access an NF service (i.e., to invoke service operations) of an NF service producer or for notifications to an NF service consumer. The Endpoint Address is defined in 3GPP TS 23.501 and TS 29.500.

The Endpoint Address is part of the service-based interface (SBI) framework, where NFs expose their services via APIs. When an NF service consumer wants to invoke a service operation on an NF service producer, it needs to know the address of the producer's service endpoint. The Endpoint Address provides this information. It can be an IP address (e.g., 192.168.1.1), an IP address with port (e.g., 192.168.1.1:8080), or an FQDN (e.g., nf.example.com). The consumer uses this address to construct the target URI, which is then used in HTTP/2 requests to the producer.

The Endpoint Address is typically discovered through the Network Repository Function (NRF). When an NF service producer registers with the NRF, it provides its Endpoint Address(es) for each of its services. The NRF stores this information and makes it available to NF service consumers upon request. This dynamic discovery mechanism allows for flexible deployment and scaling of NFs. The Endpoint Address can also be configured statically in some cases, but dynamic discovery is preferred in cloud-native environments.

In addition to service invocation, the Endpoint Address is used for notifications. When an NF service consumer subscribes to notifications from an NF service producer, it provides its own Endpoint Address so that the producer can send notifications to it. This ensures that the consumer can receive asynchronous updates about events it is interested in. The Endpoint Address thus plays a dual role: it identifies the producer's service endpoint for requests and the consumer's endpoint for notifications.

The format of the Endpoint Address has evolved. In Rel-15, it was defined as 'an address used by a NF service consumer to access the NF service provided by a NF service provider. An Endpoint Address is represented in the syntax of Uniform Resource Identifier (e.g. part of Resource URI of the NF service API).' In Rel-16, the definition was refined to explicitly include IP address, transport and port information, or FQDN, and to clarify its role in determining the host/authority part of the target URI. In Rel-20, the definition was further simplified to remove the mention of transport and port information, reflecting the use of standard HTTP/2 over TCP. These changes reflect the maturation of the SBA and the adoption of standard web technologies.

Purpose & Motivation

The Endpoint Address exists to solve the problem of service discovery and invocation in the 5G Service Based Architecture. In traditional mobile networks, interfaces between network elements were point-to-point and statically configured. With the introduction of SBA in 5G, network functions became services that can be deployed dynamically and scaled elastically. This required a flexible mechanism to discover and address these services. The Endpoint Address provides this mechanism by allowing NF service producers to advertise their service endpoints and NF service consumers to discover them.

Before the Endpoint Address concept, network elements were addressed by fixed identifiers such as IP addresses or SS7 point codes. These were manually configured and did not support dynamic scaling or relocation. The Endpoint Address, combined with the NRF, enables automatic registration and discovery of services, which is essential for cloud-native deployments where NFs can be instantiated, scaled, and terminated dynamically. It also supports multi-vendor interoperability by standardizing the format of the address and the discovery procedures.

Furthermore, the Endpoint Address is crucial for enabling notifications in a service-based architecture. In a distributed system, services need to communicate asynchronously. The Endpoint Address allows a consumer to tell a producer where to send notifications, ensuring that events are delivered to the correct instance. This is particularly important in 5G for services like mobility management, session management, and policy control, where timely notifications are essential for maintaining service quality and responsiveness. The evolution of the definition from Rel-15 to Rel-20 reflects the ongoing refinement of the SBA to align with web technologies and to simplify implementation.