This paper presents a 100% Java middleware that aims to offer an open and extensible foundation for building large-scale real-time networked virtual environment applications. This platform relies on a partial replication model in which the whole simulation space is spread on a federation of processes based on application-specific criteria. A configurable event communication framework allows arbitrary consistency and synchronization protocols to be implemented in close cooperation with the application semantics. This middleware has been experimented with success for multi-player game prototypes involving both human-driven and autonomous simulated entities.

One of the major requirements of distributed multimedia applications is the need to maintain often complex, real-time synchronization constraints. More specifically, it is necessary to be able to manage arbitrary intra- and inter-media synchronization across activities in the distributed environment. Furthermore, it is important that such developments are integrated into emerging object-oriented standards for distributed computing. This paper presents an object-oriented programming model and associated implementation to meet these requirements. The main concepts behind the proposed approach are, firstly, the use of reactive objects for real-time control and synchronization and, secondly, quality of service controlled bindings for predictable communication between objects. The flexibility of the approach is demonstrated by three contrasting examples of real-time synchronization. The implementation extends the real-time capabilities of the Chorus micro-kernel by introducing the concepts of rtports, rthandlers and quality of service controlled connections. The paper demonstrates how reactive objects and bindings are realized on this infrastructure.

There is currently considerable interest in developing multimedia applications in open distributed systems. However, it is now becoming clear that existing architectures for open distributed systems do not support the particular requirements of continuous media types such as digital audio and video. This is particularly the case in the important areas of quality of service support and real-time synchronization. This paper presents results from the Sumo project which aims at supporting continuous media types within the framework defined by the draft Open Distributed Processing standard. The paper advocates the use of synchronous languages within this framework for specifying and implementing real-time synchronization and QoS monitoring. A computational model and the realization of an infrastructure supporting this view are presented.

The programming of real-time systems with synchronous languages requires an infrastructure support, which we call a "synchronous execution machine". The role of a synchronous execution machine is to manage the interfacing of synchronous programs with their asynchronous environment, while respecting their synchronous semantics. Using the ESTEREL language as an example, we give a formal description of a generic execution machine and we discuss some aspects of its implementation on the Chorus distributed operating system micro-kernel.>