wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

13-4 Industrial Communication Systems
complex communication protocols. However, from the user’s point of view, it was the sheer simplicity
of the web browser concept that was so appealing. This tool is easy to use, platform independent, and
allows to access distant sites and data in a nearly trivial manner. It is no wonder that the easy way of
navigating through hypertext documents in the Internet was soon taken as a model for the (remote)
access to automation data, and actually many solutions available on the market today rely on WWW
technology and web browsers as an interface. Still, the impression that “the Internet” naturally entails a
uniform way of remote access to automation networks is deceptive. The user interface is only one aspect,
the underlying mechanisms and data structures are another. In fact, when it comes to implementing an
interconnection between IP-based networks and a fieldbus, there is a surprising variety of possibilities
even in the so much “standardized” Internet environment. In particular, the web-based approach is by
no means the only one.
The very recent years brought again a technology push in field-level networking. Together with the
last phase of fieldbus standardization, Ethernet solutions for industrial use appeared at the turn of the
century. One of the main arguments for their introduction was the promising—vertical—integration
possibility in company LANs. Although marketing campaigns tried to paint a bright future of Ethernet
solving all problems in vertical integration, standard Ethernet obviously lacks real-time capabilities,
which is an obstacle for field-level use. As a response to these deficiencies, new real-time networks based
on Ethernet were developed that broke with the original definition and can be expected to replace several
of today’s fieldbus systems in the long run.
What does all this mean for vertical integration? From a technology point of view, all basic elements
needed are finally available—contrary to the situation in the CIM era. What is required today is to put
them together in a reasonable way. The technological issues involved are considered in the subsequent
sections. A further challenge lurks in the application level. Figure 13.1 also shows how typical functional
units are associated with the individual levels. It appears that vertical integration is reasonably advanced
in both the upper and lower layers. This is not surprising since the two sections mirror two different
worlds inside a company:
• Business-oriented applications like enterprise resource planning (ERP) tools, supply chain management
(SCM), or financial tools for accounting and bookkeeping are tightly integrated today.
The users as well as the developers of such software tools share an economics background and are
focused on a strategic view of the company.
• Production-oriented applications like supervisory control and data acquisition (SCADA), production
control, assembly, or to a certain extent also manufacturing execution systems (MES) belong
to the operational world. Again, they are mostly well integrated, but the background of users and
developers is typically engineering, which stipulates an entirely different view on the overall system.
Figure 13.1 demonstrates that these two worlds are also separated by different networking concepts.
In the business context, LANs are predominant whereas the control level is home of the fieldbus. Again,
this is not surprising because one of the major design guidelines for fieldbus systems was the recognition
that in a (real-time) process control context, completely different networking characteristics are
required than in the (strategic) office world. Hence, the gap to bridge today not only concerns the linking
of two different network types but also the interconnection of two different mindsets.
13.3 Network Interconnections
The implementation of communication networks has been designed for particular levels of the communication
hierarchy, using dedicated I/O buses and fieldbuses at the lowest level. Typically, intermediate
levels have been using other, tailored communication systems up to the highest level. Process data has
been abstracted and processed from level to level. Network interconnections usually served horizontal
communication, i.e., the exchange of data on the same level in the hierarchy, mostly within the same
technological domain.
© 2011 by Taylor and Francis Group, LLC