Originating IP Multimedia CAMEL Subscription Information

Description

O-IM-CSI is a crucial subscriber-specific dataset within the 3GPP IMS architecture that enables the delivery of operator-defined, network-centric intelligent services. It is a type of CAMEL Subscription Information (CSI) tailored for the IP Multimedia Subsystem. This data is permanently stored in the user's profile within the Home Subscriber Server (HSS) and is dynamically downloaded to the Serving Call Session Control Function (S-CSCF) during the user's IMS registration process or when the S-CSCF needs to service an originating session for that user. The O-IM-CSI acts as the configuration or 'trigger list' that personalizes the behavior of the O-IM-BCSM (Originating IP Multimedia Basic Call State Model) for that particular subscriber.

The information contained within O-IM-CSI primarily includes the address of the gsmSCF (the node hosting the CAMEL service logic, such as an SCP) and a detailed trigger profile. This profile specifies which Detection Points (DPs) within the O-IM-BCSM state machine are 'armed' for this subscriber. When the S-CSCF, while processing an originating SIP session (e.g., a call initiation), reaches an armed DP, it suspends normal call processing. It then formulates a CAP (CAMEL Application Part) operation, such as an InitialDP, and sends it to the gsmSCF address specified in the O-IM-CSI. The gsmSCF executes its service logic—which could involve querying databases, applying charging rules, or modifying call parameters—and sends instructions back to the S-CSCF on how to proceed.

Architecturally, O-IM-CSI is a key component of the IMS service control framework, sitting at the intersection of subscriber data management (HSS), session control (S-CSCF), and service execution (gsmSCF). Its role is to dynamically link a subscriber to their subscribed services. Without O-IM-CSI, the S-CSCF would have no knowledge of which subscribers require CAMEL interaction and would process all calls using default, non-intelligent procedures. It is a fundamental enabler for personalized services like IMS pre-paid, outgoing call barring, number portability resolution, and lawful interception triggers for originating sessions. The data is transferred from HSS to S-CSCF via the Cx interface using the Diameter protocol.

Purpose & Motivation

O-IM-CSI was created to provide a subscriber-specific mechanism for intelligent service triggering in the IMS, mirroring the successful CSI concept from the circuit-switched GSM/UMTS domain. In pre-IMS networks, O-CSI (Originating CSI) allowed the MSC to invoke services for outgoing circuit-switched calls. As networks evolved to IMS, there was a clear need for an equivalent data structure that would work with the SIP-based O-IM-BCSM in the S-CSCF. The purpose of O-IM-CSI is to decouple service logic from core session control, enabling flexible and personalized service deployment.

It solves the problem of how to efficiently and dynamically inform the session controller (S-CSCF) about which users have which intelligent services, and precisely when during call setup those services should be invoked. Without such a standardized data container, service triggering would require static configuration in network elements or be impossible, severely limiting service agility. O-IM-CSI allows operators to define services centrally (on the gsmSCF) and simply update subscriber profiles in the HSS to activate or modify them, without needing to reconfigure every S-CSCF in the network. Its creation was motivated by the requirements for mass service customization, rapid service provisioning, and the seamless migration of millions of existing CAMEL service subscriptions from the circuit-switched to the IMS environment.

Key Features

• Stored in HSS as part of the IMS subscriber profile
• Downloaded to S-CSCF via Diameter Cx interface
• Contains the address of the service control gsmSCF
• Defines a trigger profile of armed Detection Points for the O-IM-BCSM
• Enables subscriber-specific invocation of CAMEL services for originating IMS sessions
• Fundamental for personalized services like IMS pre-paid and outgoing call screening

Evolution Across Releases

Defining Specifications