Service Capabilities

Description

Service Capabilities is a term used in 3GPP specifications to describe the bearers, defined by parameters, and/or mechanisms needed to realise services. These capabilities are within networks and under network control. The definition appears in specifications such as 21.905 (Vocabulary), 22.105 (Services and Service Capabilities), 22.121 (The Virtual Home Environment), 22.127 (Service Requirement for the Open Service Access), 23.127 (Virtual Home Environment/Open Service Access), 23.198 (Open Service Access (OSA); Stage 2), and 29.198 (Open Service Access (OSA); Application Programming Interface (API)). Service Capabilities are fundamental to the concept of the Virtual Home Environment (VHE) and Open Service Access (OSA), where they provide a standardized way for applications to access network functionality.

In essence, Service Capabilities are the building blocks that networks expose to enable the creation of services. They abstract the underlying network complexity and provide a set of functions that can be invoked by applications. For example, a Service Capability might be a call control function, a user location function, or a messaging function. These capabilities are defined by parameters that specify their behavior and are implemented by mechanisms within the network. The network retains control over these capabilities, ensuring that policies and resource management are enforced. This concept is central to the OSA/Parlay architecture, where Service Capability Features (SCFs) are exposed via APIs to third-party application developers.

The definition of Service Capabilities has remained largely unchanged across 3GPP releases from R99 to Rel-19, with only minor capitalization differences. In R99, the definition started with a lowercase 'bearers', while from Rel-4 onwards it was capitalized to 'Bearers'. This minor editorial change does not alter the meaning. The stability of the definition reflects the enduring importance of the concept. Over time, the specific Service Capabilities have evolved with new technologies, such as the introduction of IP Multimedia Subsystem (IMS) capabilities, location services, and later 5G service-based architecture capabilities. However, the fundamental idea of exposing network capabilities through standardized interfaces remains.

Service Capabilities are typically organized into Service Capability Features (SCFs), which are grouped into Service Capability Servers (SCS). These servers provide the implementation of the capabilities and expose them through APIs. The OSA/Parlay APIs define a set of interfaces for applications to access these capabilities. For example, the Call Control SCF allows applications to initiate, manage, and release calls. The User Interaction SCF allows applications to interact with users via voice or text. The Terminal Capabilities SCF allows applications to query terminal capabilities. These capabilities enable rapid service creation and deployment, as developers can focus on application logic without worrying about network details.

In summary, Service Capabilities are the network's exposed functions that enable service realization. They are defined by parameters and mechanisms, and are under network control. They are essential for the Virtual Home Environment and Open Service Access, and they continue to be relevant in modern networks, including 5G, where the service-based architecture exposes network functions as services. Understanding Service Capabilities is key to understanding how services are created and delivered in a controlled and standardized manner.

Purpose & Motivation

The concept of Service Capabilities was created to provide a standardized way for applications to access network functionality, enabling rapid service creation and deployment. Before this concept, service creation was tightly coupled with specific network technologies, making it difficult for third-party developers to create services. The introduction of Service Capabilities, particularly in the context of the Virtual Home Environment (VHE) and Open Service Access (OSA), solved this by abstracting network functions into reusable capabilities that could be accessed via open APIs. This allowed developers to create services without deep knowledge of the underlying network, fostering innovation and reducing time-to-market. Service Capabilities also enable network operators to expose their assets in a controlled manner, ensuring that policies and resource management are enforced. The stability of the definition across releases highlights its fundamental role in service delivery.