Event Detection Point

Description

An Event Detection Point (EDP) is a fundamental building block in 3GPP's Intelligent Network (IN) and IP Multimedia Subsystem (IMS) service architectures, specifically within the CAMEL and SIP-based service control paradigms. It defines a precise moment or state within the processing of a call, session, or user activity where the network's service logic can interact with the call/session control. EDPs are configured within the network's switching or session control nodes, such as the MSC (Mobile Switching Centre) for circuit-switched calls or the S-CSCF (Serving Call Session Control Function) for IMS sessions. When the call/session processing reaches a point marked as an EDP, the control node (the Service Switching Function, SSF) can trigger an interaction with an external service logic entity, typically the Service Control Function (SCF) or Application Server (AS).

The operation of an EDP is governed by a pre-established service logic profile or initial filter criteria. The control node (e.g., MSC, S-CSCF) monitors the call state and, upon encountering an EDP, suspends its normal processing. It then formulates a service request, encapsulating relevant call/session data, and sends it to the designated SCF/AS. This interaction allows the external service logic to make decisions that influence the call flow, such as applying charging, modifying routing, playing announcements, or collecting user input. The SCF/AS responds with instructions (e.g., Continue, Connect, Release), which the control node then executes, resuming the call processing accordingly.

EDPs are categorized primarily into two types: EDP-R (Request) and EDP-N (Notification), introduced in later releases, but the foundational EDP concept encompasses the detection and reporting mechanism itself. They are crucial for enabling a decoupled service architecture where service logic resides in dedicated, reusable application servers rather than being hard-coded into switching equipment. This model allows for rapid creation, modification, and personalization of services without requiring upgrades to every network switch. EDPs are defined for various call/session events, such as call origination (O-BCSM), call termination (T-BCSM), and specific mid-call events like called party answer or disconnect.

Purpose & Motivation

The Event Detection Point concept was created to address the limitations of traditional telephony networks where services were tightly integrated and hard-coded into monolithic switching systems. This made the introduction of new services slow, expensive, and vendor-dependent. The Intelligent Network (IN) concept, standardized by ITU-T and adopted by 3GPP as CAMEL, introduced a layered architecture separating the call control function (Service Switching Function) from the service logic (Service Control Function). EDPs are the critical 'hooks' or triggers within the switch that enable this separation.

By defining specific, standardized points in a call model where control can be passed to an external entity, EDPs solve the problem of service inflexibility. They allow network operators to deploy centralized service platforms (SCPs) that can control calls routed through many different switches from various vendors. This architecture is essential for implementing complex, network-wide services like real-time prepaid billing, virtual private networks (VPN), freephone numbers, and number portability. The creation of EDPs motivated the development of a vibrant ecosystem of value-added services, moving beyond basic voice telephony. In the evolution to IMS, the EDP concept was adapted to SIP session control, ensuring continuity of intelligent service control in all-IP networks.

Key Features

• Defines precise points in call/session state models (e.g., O-BCSM, T-BCSM) for service interaction
• Enables decoupling of service logic (SCF/AS) from bearer control (MSC, CSCF)
• Supports suspension of call processing while awaiting instructions from service logic
• Carries relevant call/session data (e.g., calling/called numbers, location) in service requests
• Allows service logic to return control instructions like Continue, Connect, or Release
• Fundamental for CAMEL and IMS Service Control (ISC) interface operation

Evolution Across Releases

Defining Specifications