Application Entity Invocation

Description

Application Entity Invocation (AEI) is a fundamental component within the 3GPP CAMEL (Customised Applications for Mobile network Enhanced Logic) architecture, specified primarily in TS 29.078. It functions as a service capability that facilitates the interaction between the core network's Call/Session Control Function and an external, operator-defined Application Entity (AE). The AE is a logical node, often part of a Service Control Point (SCP) or Application Server (AS), which hosts the custom service logic. The invocation mechanism is governed by a CAMEL Subscription Information (CSI) profile stored in the HLR/HSS, which instructs the serving network node (like a gsmSCF) to establish a dialogue with the designated AE at predefined Detection Points (DPs) in the call or session state model.

Operationally, when a subscriber initiates or receives a call/session, the visited Mobile Switching Centre (MSC) or Call Session Control Function (CSCF) checks for active CAMEL triggers. If an AEI-related CSI is present, the gsmSCF (or its equivalent) acts as the CAMEL Service Environment (CSE) and initiates a transaction with the external AE. This involves sending an initial DP (IDP) operation containing call details and subscriber data. The AE then executes its service logic—which could involve querying a database, applying charging rules, or modifying routing decisions—and returns instructions to the gsmSCF. These instructions, conveyed via CAMEL Application Part (CAP) operations like Continue, Connect, or ApplyCharging, direct the core network on how to proceed with the call handling.

The architecture relies on the standardized CAMEL Application Part (CAP) protocol, an extension of SS7/INAP, for signaling between the gsmSCF and the AE. AEI is not a service itself but a generic invocation framework that enables services like prepaid charging, fraud control, VPN services, and location-based routing. Its design separates service logic from basic call processing, allowing for rapid service deployment and customization without modifying every switch in the network. The AEI capability is integral to the Intelligent Network (IN) concept within 3GPP systems, providing a standardized, vendor-independent method for operators to create and manage value-added services.

Purpose & Motivation

AEI was created to address the need for flexible, operator-specific service creation and deployment in mobile networks, moving beyond the rigid, switch-embedded features of early systems. Prior to CAMEL and capabilities like AEI, introducing new services required proprietary, per-vendor switch upgrades, which were slow, costly, and hindered interoperability. The Intelligent Network (IN) paradigm, which CAMEL implements for GSM and later 3GPP systems, aimed to decouple service logic from core switching functions. AEI provides the specific mechanism to 'invoke' this external logic, solving the problem of how to dynamically trigger custom applications during a call or data session based on subscriber profiles and real-time events.

Historically, as mobile networks evolved and competition increased, operators demanded the ability to rapidly deploy differentiated services like prepaid billing, virtual private networks for businesses, and intelligent call routing. AEI, as part of the CAMEL framework introduced in 3GPP Release 8 and earlier, standardized this invocation process. It solved the limitations of monolithic network architectures by defining a clear, protocol-based interface (CAP) between the network's call control and external application servers. This allowed operators to develop or procure services independently from their network infrastructure vendors, fostering innovation and reducing time-to-market for new revenue-generating features.

Key Features

• Dynamic triggering of external application logic based on CAMEL Detection Points (DPs)
• Uses the standardized CAMEL Application Part (CAP) protocol for signaling
• Enabled by CAMEL Subscription Information (CSI) stored in the HLR/HSS
• Supports a wide range of services including prepaid charging, VPN, and intelligent routing
• Decouples service logic from core network switching functions
• Provides a vendor-independent framework for service creation and deployment

Evolution Across Releases

Defining Specifications