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 quality of service expected fundamentally depend on the applications. This article traces this technology from its beginnings, which go back to the first industrial networks in the 1970's. 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.

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 ofapplications.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 offunctions (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 offinding 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? "

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