Characterizing Temporal Consistency In A Fieldbus Environment

Fieldbus is a real-time network intended to be employed in the lowest hierarchy level of factory automaticin. In this paper, we give an overview of a typical Fieldbus application, and present briefly different communication models. We then explain why temporal consistency probllems arise in distributed realtime systems; we introduce the notion of validity time as an aid to precise temporal consistency, and discuss possible mechanisms to assure the validity and consistency of data. Finally, in a case study based on a prototype implementation of a Fieldbus developed at our laboratory, we show how we assure the temporal consistency and how we derive lower bounds for the validity time.