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“We believe that our strengthened relationship with ODVA will make Ethernet/IP the most widely used industrial network.” The general consensus seems to have been that this year’s Hanover Fair, incorporating the last vestiges of the once mighty Interkama, was a pretty low-key affair, at least as far as the automation industry was concerned.
That’s strange because we may look back on the week of the show, April 16-20, 2007, and the one which preceded it as the time when the automation industry finally saw sense and began to react to what its users had been telling it since at least the early 1990s: that what they really want is a single fieldbus standard that enables them freely to mix and match best of breed devices from multiple vendors within the same installation.
IEC 61158 Legacy
Of course that’s not what they’re going to get—any chance of that finally disappeared with the IEC’s decision back in 2000 to ratify, in IEC 61158, a fieldbus standard incorporating not one, but eight competing and incompatible protocols. Since then any promising moves toward rationalization, such as the decision of the major fieldbus organizations to cooperate in the development of a common Electronic Device Description Language (EDDL), have been followed almost immediately by a spectacular falling out, most recently over whether there was any benefit to be had from what Emerson Process Management President John Berra described as “this FDT nonsense.”
But then conventional fieldbus is not the only game in town. Even before the ink was dry on IEC 61158, it was becoming clear that many users were more interested in the potential of industrialized versions of the already ubiquitous Ethernet, and so it has proved. Moreover, while the conventional fieldbus power brokers have tried to extend their existing fiefdoms into Industrial Ethernet territory, we have not seen the repeat of the “fieldbus wars” that many had predicted. That’s due in part to the fact that it’s a whole lot more difficult to lock users into a particular flavor of what is already a universal standard and also, and possibly consequentially, because this time around users have made it clear that they simply won’t stand for it.]
So the announcement by Schneider Electric, the week before Hanover/Interkama that it is to become a “principal member” of the Open DeviceNet Vendor Association (ODVA) and that coincidentally ODVA is to extend its Common Industrial Protocol (CIP) network specifications to provide compatibility with Modbus/TCP is hugely significant and a triumph for user power.
Like so many such announcements, this one needs a bit of decoding. Schneider, through its ownership of the Modicon brand, is in effect custodian of the Modbus protocol, although the intellectual property and responsibility for its maintenance and development have been vested in the independent Modbus–IDA consortium since 2004.
As such its position is pretty much a mirror image of that of Rockwell Automation, which developed the CIP-based DeviceNet and ControlNet and then passed them over to the independent Open DeviceNet Vendors Association (ODVA). Since then ODVA has, at one extreme, adapted CIP as the basis of its Industrial Ethernet implementation, Ethernet/IP, and at the other, to its recently released sensor–actuator bus and ASi rival, CompoNet. Just how independent of their respective parents are these two organizations is debatable, although the cynical answer would probably be, “At least as independent as Profibus International is from Siemens.”
Developed originally in the late 1970s, Modbus’ claim to be regarded as a fieldbus is tenuous in the extreme, but its very simplicity and almost universal acceptance has sustained its popularity.
Modbus IDA claims more than 7 million Modbus nodes in Europe and North America, and that popularity has in recent years extended to the Industrial Ethernet implementation. ARC’s most recent study of the market in 2005 showed Modbus/TCP and EtherNet/IP to be the most widely supported industrial Ethernet protocols.
We asked ARC’s Harry Forbes whether that justified ODVA’s claim that the two protocols between them accounted for more than 50% of the market but he, perhaps understandably, wouldn’t be drawn, only saying that “We are working on that data for a new study to be published later this year … with node counts of all the IE flavors.”
Clearly the implication of the ODVA claim is that a combination of Ethernet/IP and Modbus/TCP would have more installed nodes than Profibus International’s (PI) ProfiNet. Back in 2004, PI’s Geoff Hodgkinson predicted that the number of ProfiNet nodes would exceed that of Profibus nodes by 2010. Given that PI is now predicting that Profibus will meet its target of 20 million nodes by 2008 with ease, we asked them what the current position was, only to get the response that they don’t know.
“We are working on the issue, but there are a number of questions to resolve, the most important being: What’s a node?” explained Carl Henning, director of ProfiNet marketing with the North American Profibus Trade Organization (PTO). “Should the count include switches? Do some technologies count each module because it has an IP address? Do others just count the overall controller? There is a real danger of trying to compare apples and oranges. We’ll have an answer to define and accurately count ProfiNet nodes probably early next year. And we’ll state our methodology (and what exactly we’re counting) then.”