Converged Charging System

Description

The Converged Charging System (CCS) is a core network function defined by 3GPP for online charging. It represents a fundamental architectural evolution from legacy, service-specific charging systems to a unified, real-time charging platform. The CCS integrates the functions of the Online Charging System (OCS) and the Charging Data Function (CDF) for online charging, providing a single point of interaction for network elements requiring real-time credit control. It operates based on the Diameter Ro and Gy reference points, interfacing with Policy and Charging Rules Functions (PCRF/PCRF), application servers, and network gateways.

Architecturally, the CCS is built around the concept of a Charging Function (CHF), which is its central logical entity. The CHF communicates with network functions via standardized service-based interfaces (e.g., Nchf) in 5G Core networks. It processes charging events in real-time, applying tariff logic, deducting funds from user accounts, and granting or denying service units based on available credit. Key internal components include the Account Balance Management Function (ABMF) for managing subscriber balances and the Rating Function (RF) for determining the monetary cost of service usage events.

Its role in the network is pivotal for monetization and service control. The CCS authorizes network resource usage in real-time before or during a service delivery, enabling prepaid, on-demand, and sponsored data services. It generates standardized Charging Data Records (CDRs) for billing and settlement. By decoupling charging logic from specific network services, the CCS allows operators to rapidly introduce and tariff new services—like 5G network slices, IoT data plans, or edge computing services—without deploying separate charging infrastructure for each.

Purpose & Motivation

The CCS was created to address the limitations of fragmented, legacy charging systems where each service type (circuit-switched voice, packet data, SMS, IMS) had its own dedicated charging platform. This siloed approach led to operational complexity, high costs, and an inability to offer unified, cross-service charging plans (e.g., shared data buckets for voice and data). The proliferation of new IP-based services and the shift towards all-IP networks (IMS) demanded a more agile and consolidated charging architecture.

The primary problem it solves is the convergence of real-time charging across all access technologies (2G/3G/4G/5G, fixed) and all service types onto a single, standardized platform. This convergence enables operators to implement innovative, personalized pricing models and launch services faster. It also provides a future-proof foundation for charging in 5G Standalone networks, where network slicing and service-based architecture require a flexible, software-defined charging function that can interact dynamically with other network functions via APIs.

Historically, its introduction in 3GPP Release 11 marked a significant step towards the full realization of the Policy and Charging Control (PCC) architecture, providing a unified online charging entity. It addressed the need for a single source of truth for subscriber credit and balance management, improving revenue assurance and reducing the risk of credit fraud across disparate service domains.