Design and implementation of an open ImS core

Mobile network operators in Europe mostly have rolled out 3G networks and are now looking into the deployment of the IP Multimedia Subsystem (IMS) which provides an overlay architecture for IP based core networks. The IMS offers a standardized way to develop new and appealing applications and may serve as a blueprint for convergent Next Generation Networks. As with the introduction of any new technology, there comes the need to measure its performance and capabilities. The Open IMS Core project introduced in this paper offers the core network functionality of an IMS for testing the performance of the central IMS network entities, the IMS Call Session Control Functions. The project's target was to build an implementation based upon open source tools that is fully conformant to existing IMS standards which may be re-used in other IMS related projects. In its setup the Open IMS Core resembles future IMS networks at the needed detail level and allowed to produce first IMS performance results.