Terminating CAMEL Subscription Information

Description

Terminating CAMEL Subscription Information (T-CSI) is a crucial data profile associated with a mobile subscriber in the Home Location Register (HLR). It contains the parameters necessary for the network to invoke CAMEL-based intelligent network services for calls terminating to (i.e., incoming to) that subscriber. When a call is routed to a subscriber, the Gateway Mobile Switching Centre (GMSC) queries the HLR to obtain routing information and subscriber data. Part of this data transfer includes the T-CSI, if the subscriber has terminating CAMEL services activated. The T-CSI is transmitted to the GMSC via the MAP (Mobile Application Part) protocol.

The T-CSI profile includes several key fields: the address of the CAMEL Service Environment (CSE) or Service Control Point (SCP) that hosts the service logic (the gsmSCF address), a list of triggering Detection Points from the T-BCSM where interaction is required, a service key identifying the specific service program to execute, and various flags and parameters for the service (like default call handling). Upon receiving the T-CSI, the GMSC configures its call processing logic accordingly. As the incoming call progresses through the Terminating Basic Call State Model (T-BCSM), the GMSC will, at the specified detection points, suspend processing and initiate a dialogue with the gsmSCF using the CAP protocol. The gsmSCF then executes the subscriber's personalized service logic, which may involve modifying the call, applying charging, or implementing features like call forwarding or screening.

T-CSI enables the personalization of services on a per-subscriber basis. Its presence in the HLR allows services to be administered centrally and applied consistently regardless of where the subscriber is roaming or which MSC is serving the call. The information is critical for revenue assurance in prepaid services, as it can trigger real-time credit checks for incoming calls. It also supports advanced call completion services like intelligent number translation or time-dependent routing. The structure and encoding of T-CSI are standardized across releases, ensuring backward and forward compatibility as CAMEL capabilities evolved through phases 1 to 4.

Purpose & Motivation

T-CSI was introduced to enable subscriber-specific control of intelligent services for incoming calls within the CAMEL framework. Before CAMEL, implementing custom behaviors for incoming calls (like personalized call forwarding) was typically a network-wide or switch-based configuration, not easily tailored to individual users. CAMEL's goal was to bring Intelligent Network (IN) flexibility to GSM. T-CSI provides the mechanism to 'subscribe' a user to these services.

It solves the problem of how to inform the visiting switch (GMSC) about which services to invoke for a particular incoming call and where to find the logic for those services. By storing this information in the HLR—the central subscriber database—it ensures the service profile is always available during call setup, even for roaming subscribers. This was a key advancement over earlier attempts at service customization, allowing operators to offer differentiated, value-added services that could be marketed individually, such as incoming call barring for prepaid users or premium call completion features.