Application Interface

Description

In 3GPP specifications, the term 'AI' serves as a standardized prefix for Application Interface class methods. It is a naming convention used within interface definitions to clearly identify methods that belong to the application layer of network functions. This prefix is applied across various technical specifications (TS) to maintain consistency in how application programming interfaces (APIs) and service-based interfaces (SBIs) are documented and implemented.

The AI prefix is typically found in the context of Open Service Architecture (OSA) and later in the Service-Based Architecture (SBA) of the 5G Core network. It precedes the actual method name, forming a complete identifier like 'AI_<MethodName>'. This structured naming helps in distinguishing application-layer operations from transport, session, or management-layer functions within complex network element interfaces. The methods themselves define the operations that an application can invoke on a network function or that network functions can expose to each other, such as service registration, discovery, invocation, and policy management.

Architecturally, interfaces using the AI prefix are part of the broader framework for enabling third-party application interaction with network capabilities, as defined in specifications like TS 23.090 (Open Service Access) and TS 23.271 (Location Services). In modern 5G systems, this concept evolves into the Network Exposure Function (NEF) and standardized APIs, but the AI prefix historically provided a clear marker for application-relevant methods within interface specifications. Its usage ensures that during system design, code generation, and testing, engineers can easily identify and handle methods intended for application-level logic and service exposure.

Purpose & Motivation

The AI prefix was introduced to solve the problem of inconsistent and ambiguous naming for application-layer methods within 3GPP interface specifications. Prior to its standardization, different working groups and releases might use varied naming conventions (like 'App', 'Srv', or no prefix at all) for similar interface methods, leading to confusion during implementation and integration between network equipment from different vendors. The prefix creates a uniform, easily recognizable pattern that denotes a method's belonging to the application interface domain.

Its creation was motivated by the need for clear, maintainable, and interoperable specifications as 3GPP networks began to expose more capabilities to external applications, starting with initiatives like the Open Service Access (OSA) and Parlay/OSA APIs. By tagging these methods with 'AI', the standards body ensured that anyone reading a technical specification could immediately understand the functional layer of the operation, streamlining the development of network elements and client applications that rely on these standardized interfaces.