Customised Applications for Mobile network Enhanced Logic

Description

CAMEL (Customised Applications for Mobile network Enhanced Logic) is a 3GPP standard that extends Intelligent Network (IN) concepts to mobile networks, specifically GSM, GPRS, UMTS, and IMS. It provides a standardized mechanism for network operators to offer operator-specific, value-added services to subscribers, even when they are roaming outside their home network. The core principle is the separation of service logic from the basic call and session control functions of the network switches (MSC/VLR, SGSN, GGSN). This separation allows for the centralized creation, deployment, and management of complex services without requiring upgrades to every network node.

The CAMEL architecture is built around the interaction between network entities using the CAMEL Application Part (CAP) protocol, which is an extension of SS7/SIGTRAN. Key functional components include the CAMEL Service Environment (CSE) or Service Control Function (SCF), which hosts the service logic, and the Service Switching Function (SSF) embedded in network switches like the MSC/VLR or GMSC. The SSF detects trigger points (Detection Points) during call or session processing and suspends the local processing to request instructions from the remote SCF via CAP. The SCF then returns instructions (e.g., connect, continue, play announcement, apply charging) to the SSF, which executes them, enabling real-time, event-driven service control.

CAMEL operates through a series of phases and trigger detection points defined for different types of calls and sessions, such as Mobile Originated, Mobile Terminated, and Forwarded calls. It supports multiple phases like call setup, alerting, answer, and disconnect. For packet-switched domains, CAMEL Phase 3 and later introduced control for GPRS sessions and SMS, allowing for services like prepaid data charging. The protocol defines a rich set of operations and parameters for charging control, event notification, and call manipulation, making it a comprehensive toolkit for IN-style services.

Its role in the network is foundational for monetization and service differentiation. It is the underlying technology enabling real-time prepaid billing, which is critical for many markets. It also supports advanced call control services like Freephone, Premium Rate, Virtual Private Networks (VPN), and location-based services. By providing a standardized interface, CAMEL ensures interoperability between equipment from different vendors and between different network operators, which is essential for seamless roaming and consistent service delivery.

Purpose & Motivation

CAMEL was created to address the limitations of traditional, switch-based service provisioning in mobile networks. Before CAMEL, advanced telephony services were implemented directly within the software of Mobile Switching Centers (MSCs), making them vendor-specific, difficult to create, and costly to deploy uniformly across a network. This approach also failed completely for roaming subscribers, as the visited network's MSCs had no knowledge of the home operator's custom services. There was a clear need for a standardized, network-wide platform to develop and execute custom service logic independently of the underlying switch infrastructure.

The primary problem CAMEL solves is enabling real-time, operator-specific service control for subscribers regardless of their location. This was driven by the commercial need for prepaid services, which require immediate credit checking and deduction during a call or data session. Without a system like CAMEL, implementing prepaid across a multi-vendor network and for roaming users was nearly impossible. CAMEL provided the architectural framework and protocol (CAP) to separate service logic (hosted in a centralized SCF) from call switching functions, allowing for centralized service creation and consistent execution at home and abroad.

Historically, CAMEL built upon fixed-line Intelligent Network (IN) standards like ITU-T's CS-1 but adapted them for the unique requirements of mobile networks, such as mobility management, handover, and roaming. Its introduction in 3GPP Release 99 (CAMEL Phase 3) marked a significant evolution, extending support to the packet-switched domain (GPRS) and SMS, thereby future-proofing the standard for data services. CAMEL addressed the limitations of previous proprietary IN solutions by creating a uniform, 3GPP-specified interface, fostering interoperability and accelerating the deployment of advanced revenue-generating services globally.

Key Features

• Real-time service control for call and session handling
• Support for prepaid/postpaid charging via standardized charging operations
• Roaming transparency for home operator services
• Protocol (CAP) for communication between Service Control and Switching Functions
• Trigger Detection Points for event-driven logic invocation
• Support for circuit-switched (voice), packet-switched (GPRS), and IMS services

Evolution Across Releases

Defining Specifications