Event Detection Point - Request

Description

Event Detection Point - Request (EDP-R) is the pivotal control-oriented subtype of the Event Detection Point within 3GPP's CAMEL and IMS service frameworks. An EDP-R represents a detection point configured for a full request-response interaction. When the call or session processing in the Service Switching Function (SSF) – such as an MSC or S-CSCF – reaches an EDP-R, it suspends all further processing of that call/session. The SSF then formulates a detailed service request, packages relevant call data (e.g., calling/called party numbers, location, service key), and sends it to the designated Service Control Function (SCF) or Application Server (AS) using protocols like CAMEL Application Part (CAP) or Diameter/SIP for IMS.

The architecture hinges on this suspension and delegation of control. The SSF enters a waiting state, holding the call resources until it receives a response from the SCF/AS. The remote service logic analyzes the request, executes its business rules (e.g., checking credit, applying call barring, determining special routing), and returns a control command. These commands are standardized instructions such as 'Continue' (proceed with normal processing), 'Connect' (route to a specific number or resource), 'ReleaseCall' (terminate the call), or 'RequestReportBCSMEvent' (arm another EDP). Upon receiving the response, the SSF executes the command and resumes the call state processing from the point dictated by the instruction. This mechanism allows the external SCF/AS to have decisive, real-time control over the call flow.

EDP-Rs are armed for critical decision points in the call model. Common examples include the 'Collected_Info' point in the Originating BCSM (after dialing digits are collected, to decide on routing), the 'O_Answer' point (to start charging), or the 'Route_Select_Failure' point (to apply alternative routing logic). The configuration of which EDPs are armed as EDP-Rs is part of the service profile downloaded to the SSF at the start of the call (e.g., via CAMEL Subscription Information). This model is the workhorse for implementing interactive, control-intensive services like prepaid billing (where every call setup and answer requires credit check and real-time charging), call screening, intelligent routing (e.g., time-of-day routing), and user interaction services (e.g., voice menus).

Purpose & Motivation

The EDP-R was developed as the core mechanism to realize the full promise of the Intelligent Network (IN) and CAMEL architecture: external, centralized control over call processing. Prior to IN, any service that required real-time decision-making (like prepaid) had to be implemented within the switch itself, leading to vendor lock-in and slow innovation. The EDP-R concept solved this by creating a standardized, protocol-based interface where the switch could literally 'ask for instructions' at defined points.

This solved critical business and technical problems. It enabled the creation of a separate, powerful Service Control Point (SCP) infrastructure that could manage services for millions of subscribers across an entire network, regardless of the switch vendors used. For prepaid services, it allowed real-time deduction of credit from a central account with immediate call termination upon exhaustion. For VPN services, it enabled complex, private numbering plans and routing logic to be centralized. The 'request' nature of EDP-R is what makes these services interactive and network-controlled rather than merely observed. The suspension of call processing, while introducing a small latency, is essential to guarantee that the service logic's instruction is applied before the call proceeds incorrectly. EDP-R is thus the enabling technology for a vast array of revenue-generating, network-hosted value-added services that defined the mobile experience beyond simple connectivity.

Key Features

• Triggers a full request-response interaction between SSF (MSC, CSCF) and SCF/AS, suspending call processing
• Enables real-time, external control over call routing, charging, connection, and termination
• Uses standardized control commands (Continue, Connect, ReleaseCall, etc.) returned by service logic
• Critical for implementing interactive services like prepaid billing, call screening, and intelligent routing
• Armed at key decision points in the Basic Call State Model (e.g., Collected_Info, O_Answer)
• Relies on CAMEL Application Part (CAP) or Diameter/SIP protocols for the service control dialogue

Evolution Across Releases

Defining Specifications