Diameter is a computer networking protocol for AAA (Authentication, Authorization and Accounting). It is a successor to RADIUS.

The purpose of the diameter credit control application is to provide a framework for real-time charging, primarily meant for the communication between gateways/control-points and the back-end account/balance systems.

 Online charging, also known as credit-based charging, is used to charge prepaid services.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. The Diameter Online Charging Application is based on IETF RFC 4006: Diameter Credit Control Application.