Distributed systems have become a focus of research in the context of real-time computing during the last few years. Specifically, application domains such as multimedia increasingly demand quality-of-service (QoS) guarantees from underlying communication networks, operating systems, and middleware platforms. Current object-oriented middleware, however, while widely appreciated for hiding the intricacies of distributed systems, falls short when it comes to support for streams of information and for end-to-end QoS. Specifically, QoS-supporting middleware should provide for location transparency with respect to high-level services, not only mere objects.

Within Squirrel we develop QoS-supporting object-oriented middleware enhancing remote object invocations as well as stream-based communication. Dynamically loadable smart proxies maintain location transparency while allowing different service implementations to utilize different communication mechanisms. Our run-time platform provides message-based real-time threading and a framework for dynamic protocol composition. Knowing that there are no silver bullets for design dilemmas we follow the open implementation design methodology wherever possible. Furthermore, operating system support for this platform is being developed, including schedulers and network protocols with reservations as well as upcalls for smooth integration of the user-level threading platform.