Description
Speech service Control (SPEECHSC) refers to the set of protocols, procedures, and functional entities within the 3GPP architecture responsible for controlling supplementary services in a circuit-switched mobile network. It operates above the basic call establishment and release procedures, handling the activation, deactivation, registration, invocation, and interrogation of services like Call Forwarding Unconditional (CFU), Call Barring (CB), and Call Waiting (CW). The control logic is distributed between the Mobile Station (MS) and the network, primarily within the Mobile-services Switching Centre (MSC) and the Home Location Register (HLR).
How it works involves a series of standardized dialogues between the user equipment and the network. A user typically activates a service like call forwarding by sending a specific sequence of digits (e.g., **21*DN#) or through a menu on the handset. This triggers a FACILITY message from the MS to the MSC, containing the supplementary service request. The MSC, often in conjunction with the HLR (which stores the subscriber's service profile), authenticates the request, checks for conflicts with other active services, and applies the service logic. The result (success or failure) is communicated back to the MS. For invocation (e.g., an incoming call being forwarded), the MSC's service control function automatically executes the logic based on the subscriber's profile and current network state.
Key components in the SPEECHSC architecture include the Call Control (CC) entity, the Supplementary Service (SS) entity in the MS and network, and the MAP (Mobile Application Part) protocol for communication between the MSC and HLR. Its role is to decouple the complex service logic from the basic switching functions, allowing for flexible introduction and management of numerous telephony features. This structured control mechanism ensures that supplementary services behave consistently across different network operators and handset manufacturers, which is essential for user experience and interoperability.
Purpose & Motivation
SPEECHSC was created to provide a standardized framework for offering value-added features beyond simple point-to-point voice calls in GSM and subsequent circuit-switched systems. The problem it solved was the proprietary and non-interoperable nature of early supplementary service implementations, which would have hindered roaming and multi-vendor network deployments. It established a common 'language' and procedure for service control.
The historical context is rooted in the intelligent network (IN) concepts of the fixed telephony world. 3GPP adapted these principles for the mobile environment, where subscriber mobility added complexity. SPEECHSC specifications (like 3GPP TS 22.977) define the stage 1 (service description) requirements, motivating the creation of detailed stage 2 and stage 3 protocols. Its creation was motivated by commercial needs: operators required differentiated services (like call forwarding to voicemail) to increase revenue and customer stickiness, and a standardized approach reduced development costs and time-to-market for both network vendors and handset makers.
It addressed the limitations of hard-coding service logic directly into switch software, which was inflexible and made introducing new services difficult. By defining a control layer, SPEECHSC enabled more dynamic service provisioning and management. While its relevance has diminished with the rise of IP-based IMS telephony, it formed the bedrock of telephony services for 2G and 3G generations.
Key Features
- Standardized control procedures for circuit-switched supplementary services
- Supports services like call forwarding, call barring, call waiting, and CLIP/CLIR
- Defines interactions between Mobile Station, MSC, and HLR
- Utilizes FACILITY messages over the radio interface for service management
- Separates service logic from basic call control for flexibility
- Ensures interoperability of services for roaming subscribers
Evolution Across Releases
Introduced the foundational concept of Speech service Control (SPEECHSC) for GSM, defining the initial set of supplementary services and the basic procedures for their activation and invocation. Established the functional split between the mobile station and the network (MSC/HLR) for service management.
Defining Specifications
| Specification | Title |
|---|---|
| TS 22.977 | 3GPP TS 22.977 |