All automation systems are now based on fieldbuses. The solutions are numerous due to the number of fieldbuses, which are in turn due to the variety of applications. This paper traces fieldbus technology from its beginnings, which go back to the first industrial networks in the 1970's. It analyzes the fieldbus requirements, in terms of functions (or services) and of performance (or quality of service). The three following types of quality of service are studied: transport, timeliness and coherence, according to the different types of traffic to ensure (or to operate). The characteristics of periodic and aperiodic traffic are described. The main international standards (IEC, ISO, CEN) are presented regarding these criteria and the main concepts issued from the OSI model. The architecture of applications and the services of the communication system have a mutual influence. This is an important point for the distribution of the application processes, and will be analyzed in regards to the possible application layer models. The architecture of the communication system itself is also studied in the hopes of finding a single system for all applications. Future developments will be considered, regarding both the end-user needs and the available technologies. And finally, to conclude, we will go back to the title and try to answer the question "Is fieldbus a technology?"

Fieldbus technology in industrial automation is not only relatively complex because of the number of solutions possible, but also, and above all, because of the variety of applications. Ironically, these in turn are responsible for the multitude of solutions available. If the analysis of the basic needs is relatively standard, as they will always involve connecting sensors, actuators, and field controllers with each other, the options in architecture are numerous and can impose the need for certain services. The required performances themselves and the QoS expected fundamentally depend on the applications. This paper traces this technology from its beginnings, which go back to the first industrial networks in the 1970s. The principal stages of development are recounted, from the initial requirement specifications to the current state of international standardization. The diverse technical solutions are then analyzed and classified. In particular, we study the temporal aspects, the medium access control protocols, and application relationships.

This account presents the foundation of PROTEUS project programme, which consists in designing and modeling of a distributed network orientation platform for integration of maintenance applications. The presentation is focused on basic requirements defining project's rationale and on the development of the platform.

In this paper we deal with a queueing model based on TDM schemes. Many results concerning this kind of model can be found in literature, but a large part of these results only concerns particular cases. Our main concern is to provide a general solution for the exact message sojourn time in the queue that should be available whatever the storage capacity may be. First, the probability distribution function as well as the Laplace transform of the message sojourn time in the buffer are derived, assuming Poisson fixed-length message arrivals, multiple output and finite buffer capacity. Second, taking advantage of these results, we provide the expected value of the message sojourn time and compare our results with those obtained by many authors. The formulas stated here are available for various particular cases especially for unlimited buffer capacity. Finally, we point out that the work done is directly usable for performance evaluation of many communication systems such as real-time networks, multiplexers and ATM links. Therefore, our results are both of theoretical and practical interests.>