CAMEL subscription information (CSI)

Description

CAMEL subscription information (CSI) is a set of data stored in the Home Location Register (HLR) or Home Subscriber Server (HSS) that identifies a subscriber as having CAMEL services. CAMEL (Customised Applications for Mobile network Enhanced Logic) is a 3GPP standard that allows operators to provide operator-specific services to their subscribers even when they are roaming outside their home network. CSI is the subscription data that triggers the CAMEL service logic in the network, enabling the execution of intelligent network (IN) services for mobile subscribers.

The CSI is used by the network to determine which CAMEL services are applicable to a subscriber and to invoke the corresponding service logic. It contains information such as the CAMEL service key, the GSM Service Control Function (gsmSCF) address, and the default call handling instructions. When a subscriber with CSI registers on the network or initiates a call, the Mobile Switching Center (MSC) or Serving GPRS Support Node (SGSN) retrieves the CSI from the HLR/HSS and uses it to trigger the CAMEL service. This allows the gsmSCF to control the call or session, providing services such as prepaid charging, virtual private networks, and location-based services.

The CSI is defined in several 3GPP specifications, including 32.240 (Charging architecture and principles), 32.250 (Charging management; Circuit Switched (CS) domain charging), 32.251 (Charging management; Packet Switched (PS) domain charging), 32.272 (Charging management; Push-to-talk over Cellular (PoC) charging), 32.276 (Charging management; Voice Call Continuity (VCC) charging), and 32.293 (Charging management; Proxy Function charging). These specifications detail the charging aspects of CAMEL services, which rely on CSI to identify subscribers and apply the correct charging models.

In the CAMEL architecture, the CSI is part of the subscriber profile and is downloaded to the serving node (MSC/SGSN) during location update or attach procedures. The serving node then uses the CSI to determine whether to trigger CAMEL services for specific events, such as call origination, call termination, or GPRS session establishment. The CSI can be configured with different service keys for different services, allowing the network to invoke different service logic based on the subscriber's subscription.

The CSI concept has evolved with the introduction of new services and network architectures. In 5G, the CAMEL subscription information is replaced by the Unified Data Management (UDM) subscription data, which includes similar information for service triggering. However, the principles of CAMEL remain relevant for interworking with legacy networks and for providing value-added services. Understanding CSI is essential for engineers working with intelligent network services and charging in mobile networks.

Purpose & Motivation

CAMEL subscription information exists to enable the CAMEL architecture, which was developed to allow mobile operators to provide value-added services to their subscribers, especially when roaming. Before CAMEL, operators could only offer services based on the home network's capabilities, and roaming subscribers had limited access to their home services. CAMEL introduced a standardized way for the home network to control services in the visited network, using intelligent network concepts.

The CSI is the subscription data that identifies a subscriber as having CAMEL services and provides the necessary information for the network to trigger those services. It solves the problem of service portability across networks, allowing subscribers to access their operator-specific services even when outside the home network. This is particularly important for services like prepaid roaming, where the home network needs to control charging in real-time.

The CSI also enables operators to differentiate their offerings and create new revenue streams by deploying custom services without requiring changes to the visited network. It provides a flexible mechanism for service invocation based on subscriber-specific data, which can be updated dynamically. The introduction of CSI in Rel-8 (and its continued evolution) reflects the ongoing need for intelligent network services in mobile networks, even as they migrate to all-IP architectures.