Basic service

Description

A basic service in 3GPP terminology refers to a bearer service or a teleservice that provides the fundamental telecommunication capability to a user. Bearer services provide the transmission capacity between access points, while teleservices encompass the complete communication capability including terminal equipment functions. The concept originates from legacy GSM specifications (GSM 01.04) and was carried into 3GPP to ensure continuity in service definitions across generations.

In the context of SIP-based networks, such as the IP Multimedia Subsystem (IMS), the identification of a basic service is derived from the Session Description Protocol (SDP) used during session establishment. SDP attributes, including media type, codec, and transport protocol, allow the network to determine which bearer or teleservice is being requested. This enables consistent service control, charging, and policy enforcement.

The basic service concept is essential for distinguishing the core service from supplementary services, which are additional features that modify or enhance the basic service. For example, a basic teleservice might be voice telephony, while supplementary services include call waiting or call forwarding. This separation allows operators to offer and charge for services independently.

Specifications such as 22.060 (General Packet Radio Service; Service description), 24.454 (TISPAN; PSTN/ISDN simulation services), and 24.654 (IMS; PSTN/ISDN simulation services) define the requirements and procedures for basic services. These specs ensure interoperability and consistent service delivery across different network implementations.

Over releases, the definition of basic service has remained largely stable, reflecting its foundational role. The term continues to be used in the context of IMS and other SIP-based networks, where SDP-based identification remains the primary mechanism for determining the requested service.

Purpose & Motivation

The concept of a basic service exists to provide a clear, standardized categorization of the fundamental telecommunication services that a network offers. It distinguishes these core services from supplementary services, which are optional enhancements. This separation is crucial for regulatory, charging, and interoperability purposes. Historically, in GSM networks, basic services were defined to ensure that essential communication capabilities, such as voice calls and data bearers, could be consistently provided and billed.

As networks evolved towards all-IP architectures, particularly with the introduction of IMS, the need to identify basic services within SIP signaling became paramount. The use of SDP to derive the service identity allows for dynamic and flexible service establishment, accommodating a wide range of multimedia services. This approach solved the problem of static service definitions that were tied to specific bearer types, enabling a more unified service framework.

The basic service concept also facilitates roaming and interworking between different networks, as it provides a common language for describing services. Without this abstraction, each network might use proprietary methods to identify services, leading to complexity and potential incompatibilities. Thus, the basic service term continues to underpin service delivery in modern 3GPP networks.