Online charging, also known as credit-based charging, is used to charge prepaid services. A typical example of a prepaid service is a calling card purchased for voice or video. The Ro protocol allows a Charging Trigger Function (CTF) to issue charging events to an Online Charging Function (OCF). The charging events can be immediate, event-based, or session-based.

Converged Application Server provides a Diameter Online Charging Application that deployed applications can use to generate charging events based on the Ro protocol. This enables deployed applications to act as CTF to a configured OCF. The Diameter Online Charging Application uses the base Diameter protocol that underpins both the Rf and Sh applications.

The Diameter Online Charging Application is based on IETF RFC 4006: Diameter Credit Control Application (http://www.ietf.org/rfc/rfc4006.txt). However, the application supports only a subset of the RFC 4006 required for compliance with 3GPP TS 32.299: Telecommunication management; Charging management; Diameter charging applications (http://www.3gpp.org/ftp/Specs/html-info/32299.htm). Specifically, the Converged Application Server Diameter Online Charging Application provides no direct support for service-specific Attribute-Value Pairs (AVPs), but the API that is provided is flexible enough to allow applications to include custom service-specific AVPs in any credit control request.