Design and Implementation of an Extensible Online Charging Architecture for the Open IMS Playground

This paper outlines the design and implementation of a prototypical IMS online charging architecture compliant to 3GPP Rel. 6 specifications for the Open IMS Playground of the Fraunhofer Institute FOKUS. It describes the integration of an IMS Gateway Function (IMS GWF) into a SIP application server to be able to carry out IMS session control for prepaid subscribers as well as service level credit management. After a brief introduction to the IMS charging concepts, the paper explains the design of the integrated IMS GWF and of the extendable Online Charging Server. It highlights the implementation details of the two components and gives some deployment and operation details. The implemented IMS online charging architecture was validated with the real-time supervision of an IMS voice call service between two subscribers.