Description
Request Report BCSM Event (RRB) is a critical operation within the CAMEL (Customized Applications for Mobile Network Enhanced Logic) protocol, which provides Intelligent Network (IN) capabilities in GSM, UMTS, and IMS networks. The BCSM (Basic Call State Model) is a finite state machine that abstractly represents the stages of a call (e.g., call initiated, alerting, answered, disconnected). The RRB operation is sent from the service control function (the gsmSCF) to the service switching function (the gsmSSF or MSC/SSP) to instruct it to monitor for one or more specific BCSM events occurring in a particular call instance.
Architecturally, when a CAMEL-triggered call is set up, the gsmSCF can send an initial RRB as part of the Connect or Continue operation. The RRB contains a list of BCSM event identifiers (e.g., "O_Answer" for originating answer, "O_Disconnect" for originating disconnect, "Route_Select_Failure"). The gsmSSF within the MSC then arms these detection points. As the call progresses and the armed event occurs, the gsmSSF interrupts the basic call processing and sends an Event Report BCSM (ERB) operation back to the gsmSCF. This report contains details about the event, such as a timestamp. Upon receiving the ERB, the gsmSCF can then apply service logic—for example, starting or stopping a charging timer, playing an announcement, or modifying the call routing.
The RRB mechanism is how CAMEL achieves real-time, event-driven control. It works through a series of request-report dialogues. A single CAMEL dialogue for a call may involve multiple RRB and ERB exchanges. For instance, an initial RRB might arm the "O_Answer" and "O_Disconnect" events for a prepaid call. When "O_Answer" is reported, the gsmSCF starts deducting credit. When "O_Disconnect" is reported, it stops the deduction and finalizes the charge. This allows the service logic residing in the network (not in the handset) to interact with and control the call flow based on its progression, enabling complex value-added services that are transparent to the end-user and the underlying switch vendor.
Purpose & Motivation
The RRB operation was created to fulfill the core promise of the Intelligent Network (IN) and CAMEL: to decouple service logic from switching functionality. Before IN, services like prepaid billing or call screening were hard-coded into the switch software, making them expensive to develop, slow to deploy, and vendor-specific. CAMEL, with operations like RRB, introduced a standardized way for an external service platform (the SCP) to control calls in real-time by being notified of key events.
It solves the problem of passive service control. Without RRB, an SCP could instruct a switch to set up a call but would have no visibility into whether the call was answered, how long it lasted, or why it failed. RRB provides this visibility by allowing the SCP to request reports on precisely those events. This enables accurate event-based charging (crucial for prepaid), sophisticated call control (e.g., time-of-day routing, fraud monitoring by detecting unusual call patterns), and seamless service portability across networks.
The historical motivation was the rapid growth of prepaid mobile services in the late 1990s. Operators needed a reliable, standardized method to implement real-time charging and control. CAMEL and the RRB/ERB mechanism became the global 3GPP standard for this, overcoming the limitations of proprietary IN solutions. It allowed operators to introduce advanced telephony services rapidly and consistently across multi-vendor network environments, forming the backbone for many commercial mobile services for decades.
Key Features
- A CAMEL operation sent from gsmSCF to gsmSSF to arm specific BCSM detection points
- Enables event-driven reporting back to the service logic via Event Report BCSM (ERB)
- Critical for real-time service control applications like prepaid charging
- Monitors call progression events (e.g., answer, disconnect, busy, no answer)
- Allows the service logic to react dynamically to changes in call state
- Standardized across 3GPP releases for consistent service implementation in GSM, UMTS, and IMS
Evolution Across Releases
Formally specified as part of the CAMEL protocol enhancements. The initial architecture defined the RRB operation within the CAP (CAMEL Application Part) protocol, enabling the gsmSCF to request reports on a standardized set of BCSM events for call control in circuit-switched domains.
Defining Specifications
| Specification | Title |
|---|---|
| TS 29.278 | 3GPP TS 29.278 |