Online charging

Description

Online charging is a charging mechanism in 3GPP where charging information can affect, in real-time, the service rendered. This means that the charging process is directly involved in the service delivery, allowing for immediate authorization, credit control, and service termination if the subscriber's account balance is insufficient. Online charging is essential for prepaid services, where subscribers pay in advance and require real-time balance management.

The mechanism involves a direct interaction between the charging system and the bearer/session/service control. When a subscriber requests a service, the charging system is consulted to check if the subscriber has sufficient credit. If so, the service is authorized, and the charging system monitors usage in real-time, deducting charges accordingly. If the balance is depleted, the service can be terminated or downgraded. This real-time interaction ensures that the operator avoids revenue loss and the subscriber is aware of their usage.

Key components of online charging include the Online Charging System (OCS), which performs real-time credit control, and the Charging Trigger Function (CTF), which detects chargeable events and communicates with the OCS. The OCS includes functions such as Online Charging Function (OCF), Account Balance Management Function (ABMF), and Rating Function (RF). The CTF can be located in various network elements, such as the Serving GPRS Support Node (SGSN), Gateway GPRS Support Node (GGSN), or Application Servers.

Online charging supports various charging models, including volume-based, time-based, event-based, and content-based charging. It can be applied to a wide range of services, from voice calls and data sessions to messaging and value-added services. The 3GPP specifications define the architecture, protocols (e.g., Diameter Credit-Control Application), and procedures for online charging, ensuring interoperability across vendors and networks.

In summary, online charging is a critical mechanism for real-time credit control and service authorization. It enables prepaid services and ensures that charges are applied accurately and immediately, benefiting both operators and subscribers.

Purpose & Motivation

Online charging was introduced to support real-time credit control and enable prepaid services in mobile networks. Before its introduction, charging was primarily offline, meaning that charges were collected after service usage, which posed risks for prepaid subscribers who might exceed their balance. Online charging solves this by allowing the network to check the subscriber's credit before and during service delivery, ensuring that services are only provided if sufficient funds are available.

The motivation for online charging also includes the need for immediate service authorization and control. For services like prepaid voice or data, it is essential to monitor usage in real-time and terminate the service when the balance is exhausted. This prevents revenue leakage and provides a better user experience by avoiding unexpected charges.

Historically, online charging evolved from the need to support prepaid services in GSM and GPRS networks. As mobile services expanded to include data and multimedia, online charging mechanisms were enhanced to handle more complex charging scenarios, such as content-based charging and event-based charging. 3GPP standardized online charging in specifications like TS 32.240 and TS 32.299, providing a robust framework for real-time charging across various network domains.