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10 December 1999
Surefire idea for open systems
by Steve Schoenberg

I have often heard it said that the most interesting thing about standards is that there are so many to choose from. We have accepted different networking standards, and we defend these choices (often with passion) because we have made large investments in our automation systems and for the most part have garnered satisfactory results. How can we achieve the goal of interoperability when we divide our efforts, supporting seemingly competitive and incompatible network standards? The solution is open networking-universal connectivity that integrates the diverse networks that have successfully built our industry.

We constantly hear arguments about why one networking solution is the perfect open standard that should make us forsake all others. This shortsighted thinking is, of course, absurd. "Open systems" by its very definition means we have choices. We need the freedom to pick the best networking solution for each application and the ability to easily modify our decision when necessary. The new era of open systems has given us a choice of hardware and software components from many vendors that fit together seamlessly. These open tools are fulfilling our wish for true interoperability. Why should we not then have the same open choice of communications as well? If only there were a way to interconnect our dissimilar networks and have them integrate smoothly. It's not hard to guess the solution is Ethernet.

The role of Ethernet

The robust performance, extreme reliability and low cost of Ethernet are well known. Also, much has been written (and demonstrated) to prove the suitability of Ethernet for most real-time automation systems. However, I believe the real miracle of Ethernet is its ability to provide the truly open systems we are looking for. Ethernet can not only support multiple protocols and network alternatives but do so simultaneously. We can now keep existing standards and diverse protocols and easily connect them.

This interconnectivity results from the unique ability of Ethernet to transport dissimilar network messages over the same highway. Any field device or computer can talk to any other device using any desired protocol, all on one common cable. This openness results from the universal acceptance of the IEEE 802.3 Ethernet standard. Also, the fact that the Ethernet integrated circuit handles all the details of packet transmission gives a system designer little reason to make alterations. Today, inside these Ethernet packets, you are most likely to find the world-standard TCP/IP. (What could be more standard than the Internet Protocol?) This open transport easily delivers messages used by the varied industrial protocols we have chosen to adopt. Now, a single Ethernet device can receive and respond to multiple protocols, from many sources, in a completely open way.

At the speed of Ethernet

One more positive aspect is that Ethernet provides an opportunity to improve the performance of existing protocols. One example is the Modbus protocol. Traditional RS-485 Modbus can have only one master, and existing systems are often slower than we would like. Modbus/TCP, however, enables any number of masters to talk to slave devices because the Modbus messages are inside TCP/IP. Now users can receive Modbus messages at Ethernet speed. Already, many popular industrial communications standards such as Foundation fieldbus and Profibus have defined or implemented Ethernet as a solution. Expect improvements similar to the Modbus enhancements in the not-too-distant future. These open solutions enable our existing installations to gracefully evolve into enterprise-level open systems.

It's all about choices

Ethernet provides connection choices at the physical layer as well. In each application, you can use a combination of coax cable, the highly popular 10Base-T (phone-style RJ-45 connector), and fiber-optic links. Recent discussions of the Industrial Automation Open Networking Alliance are pointing the way to new ruggedized industrial solutions as well. In addition, inexpensive gateway boxes are appearing on the market to connect existing networks onto an Ethernet backbone. Gateways exist to link existing serial Modbus devices to Ethernet.

All of the necessary elements for truly open communications are rapidly coming together. The existing communications standards are now finding common ground through Ethernet connectivity. In support of these efforts, new technology development is keeping pace with our requirements for smarter, faster, and more economical systems. It's quite remarkable to discover that no matter which protocol and network connection you select for your open systems, it will be hard to go wrong.

Additional Information

Author Information

Steve Schoenberg is president and a founder of SIXNET. He has developed advanced automation technology throughout the company's 24-year history. Schoenberg is a licensed P.E.