OSIMS - The FOKUS Open Source IMS Core

It has to be noted that this Open Source IMS Core System is not intended to become or act as a product in a commercial context! Its sole purpose is to provide an IMS core reference implementation for IMS technology testing and IMS application prototyping for research purposes, typically performed in IMS test-beds. This target has also motivated the decision to use open source software (i.e. SER based on GPL), which makes a product development quite unattractive.

Furthermore, users of the Open Source IMS Core System have to be aware that IMS technology may be subject of patents and license terms, as being specified within the various IMS-related IETF, ITU-T, ETSI, and 3GPP standards. Thus all Open Source IMS Core System users have to take notice of this fact and have to agree to check out carefully before installing, using, and extending the Open Source IMS Core System, if related patents and licenses may become applicable to the intended usage context.

As IMS (IP Multimedia Subsystem) is today already in trial phases with more and more operators worldwide, R&D efforts with respect to NGNs are likely to gain even more support within a broader audience soon - especially for developing services. While there are already many Open Source projects established in the plain VoIP area for SIP clients, proxies, stacks and tools around the IETF SIP standards, there are currently practically no Open Source projects with specific focus on the IMS.

The Open Source IMS Core project of the Fraunhofer Institute FOKUS aims to fill the currently existing IMS void in the Open Source software landscape with a flexible and extendable solution that has already proven its conformance and performance in several national and international R&D projects. Its goal for the coming months is to create a developer community for Next Generation Network core elements within R&D and IMS interested parties. The idea for users of this Open Source software is to enable the development of IMS services and the trial of concepts around core IMS elements that are based upon highly configurable and extendable software.

The Open Source IMS Core in the Open IMS Playground

The Open Source IMS Core consists of Call Session Control Functions (CSCFs), the central routing elements for any IMS signaling, and a Home Subscriber Server (HSS) to manage user profiles and associated routing rules. The central components of the Open Source IMS Core project are the Open IMS CSCFs (Proxy, Interrogating, and Serving) which were developed at FOKUS as extensions to the SIP Express Router (SER) in recent months and successfully tested for interoperability with commercial IMS products in the Open IMS Playground. But since even basic signaling routing functionality for IMS requires information look-up in a HSS, normal usage of such a core IMS network is not possible without it, therefore a simple HSS, the FOKUS Home Subscriber Server (FHoSS) is also part of the Open Source IMS Core project.

The Open Source IMS Core project will provide a 3GPP IMS Service Control (ISC) interface to developers allowing them to make use of IMS routing features, application of IMS triggering rules and other IMS related features. It enables the application layer development of IMS services for various platforms, be it for SIP Application Servers, an OSA/Parlay resp. Parlay X Gateway or even an IN service (connected to the IMS via an IMS Service Switching Function). But also towards the access network layer, the Open Source IMS Core enables the development of components and concepts that come with the attachment of various access networks to the overlay architecture IMS.

The Open Source IMS Core project of the Fraunhofer Institute FOKUS was officially launched on November 16, 2006 in conjunction with the 2nd International FOKUS IMS Workshop as an Open Source initiative which will be hosted on the BerliOS platform at www.openimscore.org.

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The licensing model for the core components will be:

• Open IMS CSCFs : GNU General Public License v.2
  
• FOKUS Home Subscriber Server (FHoSS): GNU General Public License v.2