Description
Call Completion Service Set-up (CCSS) is a standardized service framework defined by 3GPP for managing enhanced call completion scenarios within the Circuit-Switched (CS) domain of mobile networks. It operates as a supplementary service within the core network, interacting with the Mobile Switching Center (MSC) and Home Location Register (HLR). The service set-up involves specific procedures and signaling flows between network entities to activate, invoke, and manage features like Call Waiting and CCBS.
Architecturally, CCSS is implemented within the MSC and potentially involves service logic in the HLR for subscriber profile management. When a call attempt encounters a busy condition (for CCBS) or a subscriber is already engaged in a call (for CW), the MSC invokes the CCSS procedures. For CCBS, the MSC stores the call request information, monitors the busy subscriber's status via mobility management, and initiates a recall to the originating party once the called party becomes idle. This involves timer management, resource reservation for the recall attempt, and appropriate charging record generation.
For Call Waiting, the CCSS framework allows the MSC to alert a busy subscriber of an incoming waiting call using a specific tone or indication, without disconnecting the existing call. The subscriber can then choose to accept, reject, or ignore the waiting call. The service set-up includes the negotiation and management of the waiting call state, handling of subscriber responses, and interaction with basic call control. CCSS procedures are detailed in 3GPP TS 29.163, which specifies the interworking between the MSC and other network elements, often focusing on the IP Multimedia Subsystem (IMS) and CS interworking scenarios in later releases.
CCSS plays a critical role in enhancing the reliability and user satisfaction of traditional voice services. By providing mechanisms to complete calls that would otherwise fail, it increases network traffic completion rates and reduces the need for repeated redialing attempts, which can congest signaling channels. Its integration requires support for specific MAP (Mobile Application Part) or Diameter signaling extensions for subscriber data management and service invocation, ensuring seamless operation across different vendor equipment and network generations where CS fallback or legacy services are supported.
Purpose & Motivation
CCSS was created to address the common user frustration and network inefficiency caused by busy subscribers and missed call opportunities in circuit-switched mobile networks. Prior to its standardization, basic call handling would simply result in a busy tone or call failure when a subscriber was engaged, leading to repeated call attempts and increased signaling load without guaranteed completion. The purpose was to introduce intelligent, network-assisted features that could automatically complete a call once conditions permitted, improving first-time call success rates and overall service quality.
The historical context lies in the evolution from basic telephony to enhanced supplementary services in GSM and UMTS networks. Features like Call Waiting and Call Hold existed but required a standardized, robust set-up and interworking procedure, especially as networks evolved towards all-IP architectures like IMS. CCSS provided a unified framework for these services, ensuring consistent behavior across different operators and network equipment vendors. It solved the problem of proprietary implementations that could hinder interoperability and roaming.
Furthermore, CCSS addressed the limitation of passive call failure by making the network active in managing call completion. For CCBS, it solved the issue of the calling party needing to manually retry a busy number repeatedly, which was inconvenient and could tie up network resources with unsuccessful attempts. By automating the recall, it optimized resource usage and improved customer experience. The framework also laid groundwork for convergence with IP-based services, as specified in TS 29.163 for IMS Centralized Services (ICS) and CS-IMS interworking, ensuring legacy call completion features could be supported in evolving network architectures.
Key Features
- Standardized activation and invocation procedures for Call Waiting (CW)
- Network-managed recall mechanism for Completion of Communications to Busy Subscriber (CCBS)
- Integration with MSC and HLR for subscriber service profile management
- Support for timer-based resource management and call queuing
- Generation of specific charging records for call completion events
- Interworking with IMS and other domains as per TS 29.163
Evolution Across Releases
Introduced CCSS as a standardized framework for Call Completion supplementary services in the CS domain, primarily for Call Waiting and CCBS. It defined the basic architecture involving the MSC and HLR, specifying service set-up procedures, triggering conditions for busy subscriber states, and initial signaling flows for call recall and waiting notification within GSM/UMTS circuit-switched networks.
Defining Specifications
| Specification | Title |
|---|---|
| TS 29.163 | 3GPP TS 29.163 |