We address the problem of middleware design for constructing ATM LAN based distributed industrial plant monitoring and control systems. In particular, we present a real-time client-server programming model based on a uniform ATM network. This model is being realized in our middleware called MidART. The middleware provides a set of industrial application specific but network transparent programming abstractions and application programming interface (API) that support individual application QoS requirements. In order to achieve on-demand transmission of plant data, we have developed a concept called selective real-time channels to be supported by MidART. We present the design and protocols of selective real-time channels and describe how QoS requirements of applications are guaranteed.

Data sampled from plants are registered as temporal data, combined with time stamps. We developed a real-time data server which periodically acquires temporal data and transmits them to clients for graphic presentation. The real-time data server consists of multi threads scheduled based on the rate monotonic theory. This paper explains the design of a real-time data server. The prediction for schedulability of it based on the rate monotonic theory has been verified with an experiment on an actual system.>

A fault-tolerant architecture for loosely coupled distributed real-time systems is considered and a distributed task management method that aims at network-wide fault tolerance, compatible with flexible resource utilization is proposed. The task management method includes a checkpoint data transfer mechanism and an adaptive task remapping mechanism. A policy of task remapping is based on the thermodynamic diffusion model, in which tasks are diffused among sound nodes and global balance is achieved by several repetitions of local load sharing. Convergence to this steady state is theoretically ensured. The protocol of the proposed task remapping algorithm, the two-phase diffusion algorithm, is completely distributed and weakly synchronized; each node starts the same algorithm periodically, without waiting for any messages, but waits for messages from neighboring nodes during execution of the algorithm.>