1.l Introduction
One of the fundamental tenets of the integration of industrial automated enterprises is unrestricted and
timely flow of data between applications at different levels of the enterprise hierarchy — for example,
between shop—floor and enterprise level — as well as between different applications at the same level.
This data exchange takes place among various IT infrastructure elements functionality and performance
requirements of which are determined by their level in the hierarchy and the application they support.
They may be controllers and operator workstations at the manufacturinglprocess level; workstations
supporting the Manufacturing Execution System application; gateway servers in between control net-
works and the plant network; workplaces at the enterprise or business level supporting, for example. the
Manufacturing Resource Planning application; etc. The primary conduit of data exchange in modern
automated systems is a specialized communication infrastructure that takes on a hierarchical arrange-