While the physical layer was standardized in 1992 in IEC
61158-2, the data link layer proved to be the area of primary disagreement throughout the 1990s, with "very significant technical differences" between the French and German approaches, according to Tom Phinney
.Phinney is Senior Fellow at Honeywell Automation & Control Solutions and technical coordinator for SC 65C, as well as convenor of its cyber-security working group (WG13) and fieldbus maintenance team (MT9).
"The French approach," says Phinney
, "was for a centrally managed distributed system with full knowledge of preplanned system load that could maintain strict cycle-to-cycle timing.
On top of that, says Phinney
, "the whole effort was complicated, fatally it turned out, because of the European Union's
ability to use CENELEC listing of approved standards as a geopolitical tool, because in the EU the purchase by regulated industries of unapproved technologies is illegal."
Resolving the issuesIn 1989, the US convenor of the IEC fieldbus working group, who was also chairman of the parallel SP50 fieldbus committee, had asked the elected editor for the future data link layer standard to draft a proposal to include the essence of each technology.The resulting compromise, described by Phinney
as "in effect a two-humped camel," was to allow the two technical approaches to co-exist and systems to be "tuned" to function similarly (but not identically) to Profibus
or to FIP, or indeed somewhere in between.
: "The requested 'merger' was achieved.
says: "All of the consortia are now able to reference the IEC standards as the basis for their work, and to contribute corrections and further developments in a uniform manner that benefits the larger worldwide automation community."
Lessons learnedWith the benefit of hindsight, perhaps the first lesson learned over the decade-plus of "fieldbus wars" was that the understandable desire of automation end-users for a single worldwide communication standard covering such a complex set of systems was as unachievable as it is in, for example, languages, modes of dress, dial-up modem data rates or forms of transport.The experience certainly also showed that standards working groups should not allow themselves to be used as proxies in marketing battles.
So while leaders in the international standards community retain some less-than-ideal memories of the past, the fieldbus battles of the 1990s are over."That experience," says Phinney
, "taught that co-operation was more fruitful than confrontation.
It may have taken a long time to get there but, as Phinney
says: "The technology wars of the 1980s and 1990s have been replaced by a more polite competition for markets.