Initial Detection Point

Description

The Initial Detection Point (IDP) is a fundamental component of the CAMEL (Customised Applications for Mobile network Enhanced Logic) architecture, which is a 3GPP standard for enabling operator-specific, intelligent network (IN) services in mobile networks. CAMEL allows service logic, often residing in a dedicated Service Control Point (SCP), to interact with the call and session control functions in the core network (like the MSC or GMSC). The IDP represents the specific, pre-defined event or state in a call or session (e.g., call attempt, SMS submission, GPRS session establishment) that triggers the core network to suspend its normal processing and request instructions from the external CAMEL service logic.

When a subscriber whose profile indicates CAMEL support initiates an activity, the serving core network node (like the MSC) monitors for the configured Initial Detection Point. Upon encountering this point, the node packages relevant information—such as the called and calling party numbers, location, and service key—into an Initial Detection Point operation. This operation is then sent via the CAP (CAMEL Application Part) protocol to the designated SCP. The SCP, containing the custom service logic, processes this request and returns instructions to the core network node. These instructions, conveyed via CAP operations like Request Report BCSM (Basic Call State Model) event, Connect, Continue, or Apply Charging, dictate how the call or session should proceed, be charged, or be modified.

Architecturally, the IDP is a key element of the CAMEL Subscription Information (CSI) downloaded to the core network from the HLR/HSS. It defines the trigger for service interaction. The IDP's role is crucial for separating service logic from switching logic, enabling rapid deployment of new services without modifying every core network switch. It is the entry point for a wide range of value-added services, including real-time prepaid charging, fraud control, virtual private networks (VPN), and location-based services, forming the bridge between the traditional circuit-switched or packet-switched core and intelligent service platforms.

Purpose & Motivation

The IDP was created to address the limitations of traditional, switch-based service provisioning in mobile networks. Before CAMEL and concepts like the IDP, new services required proprietary, vendor-specific implementations directly within each Mobile Switching Centre (MSC), making deployment slow, costly, and inconsistent across a network. The purpose of the IDP is to provide a standardised, well-defined trigger mechanism that allows an external, centralised service platform (the SCP) to intervene in call and session control.

This solves the problem of service portability and rapid innovation. It enables network operators to develop and deploy customised, intelligent services independently of their core network infrastructure vendors. The IDP, as the initial trigger, is the catalyst for this interaction. It specifically solves the need for a controlled, standardised point of interaction where service logic can be invoked based on subscriber profiles, allowing for sophisticated service control, real-time charging, and personalised features that were difficult or impossible to implement in a purely switch-centric model. Its creation was motivated by the competitive need for operators to differentiate their offerings and the technical need for a more flexible, open service architecture akin to the Intelligent Network (IN) concept from fixed telephony, but adapted for the mobility and roaming context of GSM and UMTS.

Key Features

• Standardised trigger point in the CAMEL call/state model
• Defined in the subscriber's CAMEL Subscription Information (CSI)
• Triggers the CAP dialogue between the core network node (gsmSSF) and the Service Control Point (SCP)
• Carries essential call/session information like calling/called party numbers and location
• Enables suspension of core network processing for external service logic instructions
• Foundation for services like prepaid, fraud management, and number translation

Evolution Across Releases

Defining Specifications