The Ethernet wars
Profibus vs. FOUNDATION fieldbus; ControlNet vs. Interbus; DeviceNet vs. SDS; Seriplex vs. AS-Interface—the bus wars continue to rage. But a new challenger has changed the battle.Ethernet, a standard in business networking since the mid-1980s, is touted by vendors and users alike as a contender for industrial applications.
Profibus vs. FOUNDATION fieldbus; ControlNet vs. Interbus; DeviceNet vs. SDS; Seriplex vs. AS-Interface—the bus wars continue to rage. But a new challenger has changed the battle.
Ethernet, a standard in business networking since the mid-1980s, is touted by vendors and users alike as a contender for industrial applications. The TCP/IP protocol over Ethernet has become the Internet standard. Recently, organizations responsible for Profibus, ControlNet, and FOUNDATION fieldbus (FF) have announced intentions to support Ethernet and TCP/IP. According to Mike Evensen, director of business development for Hirschmann Network Systems, these groups are getting involved with Ethernet because their users are requesting faster, open, interoperable networking with worldwide support.
Wrapper technology is being used as the fastest way to get traditional fieldbuses on Ethernet. Developers take the core functionality of the network and "wrap" it in a TCP transportation frame, compatible with existing Ethernet infrastructure.
Says Mr. Evensen, "In the short term, the automation marketplace will have competitive TCP/IP solutions that are not interoperable. However, if the physical architecture is the same, there's still a huge benefit to the end-user."
For example, two PLCs running two different application layer protocols, such as FF or Profibus, could sit on the same wire but they could not communicate with each other. Ethernet is merely the transmission highway. As an analogy, coworkers need common application software to share a PC-based file on the company intranet. Similarly, control devices need compatible communication software to share information over the same Ethernet wire.
Additionally, automation applications require network hardware that can withstand harsh demands of the industrial environment. Hirschmann has developed "hardened" Ethernet switches, which are hardware solutions that prevent data collisions on the network. A 10-port switch, that might link one PLC and nine I/O blocks, provides each port with a free access lane to the Ethernet highway.
"For Ethernet to be successful in industrial automation," says Mr. Evensen, "you must have these three things:
Fast Ethernet (100 Mbit/sec) to guarantee performance;
Ethernet switching to prevent collisions; and,
A prioritization scheme to deliver determinism."
Control manufacturers, in the near term, will deliver solutions based on traditional networks, even if they do run on Ethernet. This will provide competitive differentiation among different vendors' products. In the future, however, we may see adoption of a standard Ethernet application protocol for automation. Whether it's FF, Profibus, ControlNet, or one of the dozen or so current and future options remains to be defined.
Connect and be counted
In the interim, Control Engineering wants to know what networks you use in your automation applications. This month we are mailing an Industrial Networking survey to a 10% sample of our readers. If you receive the survey, please take a few minutes to complete it and send it back. Other readers who would like to participate can complete the survey on our web site at www.controleng.com/network.htm . We'll award a Palm Pilot in a random drawing of web site survey participants.
Results will be published in a special report to our readers with our March 1999 issue. Thank you for participating in a survey designed to define the industrial networking marketplace. Your answers will help deliver better solutions for your networking systems.
Jane S. Gerold, Editorial Director firstname.lastname@example.org