Charge Generation Point

Description

The Charge Generation Point (CGP) is a critical component within the 3GPP charging architecture that serves as the central entity for generating standardized charging data records. It operates within the Offline Charging System (OFCS) framework and is responsible for receiving, processing, and formatting charging information from multiple network elements before forwarding it to the billing domain. The CGP acts as an intermediary between network functions that generate charging events and the billing systems that process them for revenue collection.

Architecturally, the CGP interfaces with various Charging Trigger Functions (CTFs) located in network elements like the MME, SGW, PGW, and application servers. These CTFs detect chargeable events and send Charging Data Requests (CDRs) to the CGP via standardized interfaces. The CGP receives these requests, validates the charging information, correlates related events from different network elements, and creates consolidated Charging Data Records (CDRs) in the appropriate format. These formatted records are then transferred to the billing system for further processing and invoice generation.

Key components within the CGP include the charging data collection module, which receives charging events from network elements; the correlation engine, which associates related charging events from different sources; the formatting module, which creates standardized CDRs; and the transfer function, which delivers completed records to billing systems. The CGP also includes validation mechanisms to ensure charging data integrity and consistency before forwarding to billing domains. It supports various charging models including time-based, volume-based, event-based, and session-based charging.

The CGP's role extends beyond simple data collection to include important functions like charging data aggregation, where it combines multiple charging events into comprehensive records; data mediation, where it transforms charging information into billing-system-compatible formats; and charging session management, where it maintains state information for ongoing charging sessions. By centralizing these functions, the CGP reduces complexity in individual network elements and provides a standardized interface to billing systems, enabling operators to introduce new services without requiring changes to their billing infrastructure.

Purpose & Motivation

The Charge Generation Point was created to address the growing complexity of charging in mobile networks as services evolved beyond simple voice calls. Prior to its introduction, charging functions were distributed across network elements, leading to inconsistent charging data formats, difficulties in correlating charging events from different network domains, and challenges in integrating new services with existing billing systems. This distributed approach made it difficult for operators to accurately bill for complex services involving multiple network elements and service components.

The CGP solves these problems by providing a centralized charging generation function that standardizes how charging information is collected, processed, and formatted. It enables operators to implement consistent charging policies across different network domains and service types, simplifies the integration of new network elements and services with billing systems, and improves the accuracy and reliability of charging data. By separating charging generation from network functions, the CGP allows network elements to focus on their primary functions while ensuring charging requirements are met consistently.

Historically, the introduction of CGP in Release 8 coincided with the transition to LTE/EPC networks and the proliferation of data services, which required more sophisticated charging capabilities than previous generations. The CGP architecture was designed to support the diverse charging requirements of IP-based services, including quality-of-service differentiation, roaming scenarios, and complex service bundles. It addressed limitations in earlier charging approaches by providing a scalable, flexible framework that could evolve with network technology and service innovation.

Key Features

• Centralized charging data collection from multiple network elements
• Standardized Charging Data Record (CDR) generation and formatting
• Charging event correlation across different network domains
• Support for multiple charging models (time, volume, event, session)
• Interface mediation between network functions and billing systems
• Charging data validation and integrity checking

Evolution Across Releases

Defining Specifications