The goal of this survey paper is to give a comprehensive
overview of how field-level networks evolved and what was
done to make this evolution continuous. Although individual
technologies were meant to be (or advertised as) radical innovations,
the overall evolution went very smoothly. Section II
deals with the development of the classical fieldbus systems,
and Section III addresses the next step, i.e., the introduction
of industrial Ethernet. Section IV discusses the challenges of
wireless networks in automation, whereas Section V is devoted
to their combination with wired systems. Section VI presents
some related research, and Section VII finally attempts to give
an outlook to the future.