Originating CAMEL Subscription Information

Description

Originating CAMEL Subscription Information (O-CSI) is a critical data element within a subscriber's profile stored in the Home Location Register (HLR). It is a set of structured parameters that instructs the Visited Mobile Switching Center (VMSC) or Gateway MSC (GMSC) on how to invoke CAMEL (Customised Applications for Mobile networks Enhanced Logic) services for calls originated by the subscriber. When a subscriber registers with the network or when a call is initiated, the HLR sends the O-CSI to the serving MSC as part of the subscriber data in the MAP Insert Subscriber Data operation. The O-CSI contains the address of the gsmSCF (the CAMEL service control node), a Service Key to identify the specific service logic program, and a list of Trigger Detection Points (TDPs) for the Originating Basic Call State Model (O-BCSM).

Upon receiving a mobile-originated call attempt, the MSC's Service Switching Function (SSF) examines the O-CSI. If the call event matches an armed TDP (e.g., DP2 'Collected_Info'), the SSF suspends call processing and initiates a dialogue with the designated gsmSCF using the CAMEL Application Part (CAP) protocol. It sends an InitialDP message containing the Service Key and call details. The gsmSCF uses the Service Key to select the appropriate service logic, which then takes control of the call, potentially instructing the MSC to continue, connect to a specific number, apply special charging, or release the call. The O-CSI may also include parameters like the Default Call Handling, which dictates whether the call should proceed or be blocked if the gsmSCF is unavailable.

The structure and content of O-CSI have evolved across 3GPP releases to support more complex services. It can include multiple gsmSCF addresses for load sharing or redundancy, criteria for which TDPs are active, and indicators for specific capabilities like suppression of announcements. It is a cornerstone of the CAMEL architecture, enabling the separation of service logic from basic call switching. By having this information dynamically provisioned in the HLR and distributed to the MSC, operators can deploy and modify services on a per-subscriber basis without needing to reconfigure every network switch, providing immense flexibility for offering personalized, intelligent network services.

Purpose & Motivation

O-CSI was created to enable the deployment of subscriber-specific, network-based intelligent services in a standardized and scalable way across GSM and UMTS networks. Before CAMEL, any advanced call handling logic was typically hard-coded into the MSC's software, making it inflexible and difficult to customize for individual subscribers or to update across a multi-vendor network. This limited operators' ability to quickly launch services like prepaid billing, which requires real-time interaction with a central account balance.

The O-CSI solves this problem by acting as a mobile-specific 'trigger profile.' It moves the intelligence of *when* and *how* to invoke a service out of the switch and into the subscriber's data. This allows a centralized service control point (gsmSCF) to control calls for any subscriber, anywhere in the network, based on the triggers defined in their O-CSI. It directly addresses the business and technical need for real-time prepaid services, which became a massive driver for mobile growth. Without O-CSI, implementing prepaid would require complex and proprietary integration at every MSC.

Furthermore, O-CSI facilitated the creation of a vibrant ecosystem of value-added services. By providing a standardized mechanism to trigger external control, it allowed operators and third-party providers to develop services independently of the underlying switch vendor. This decoupling accelerated innovation, enabling services like virtual private networks, fraud management, call screening, and location-based services. Its continued evolution through numerous 3GPP releases underscores its fundamental role in enabling programmable service control in mobile networks.

Key Features

• Stored in HLR and downloaded to MSC/VLR as part of subscriber data
• Contains the address of the gsmSCF (service control node)
• Includes a Service Key to identify the specific service logic
• Lists Trigger Detection Points (TDPs) for the O-BCSM
• May define Default Call Handling for SCF failure scenarios
• Enables subscriber-specific, real-time invocation of CAMEL services

Evolution Across Releases

Defining Specifications