When discussing various industrial Ethernet protocols, spokespeople from Rockwell (and occasionally now Schneider) like to use the phrase about competing protocols, "it corrupts the stack." The best explanation I have received is that "only EtherNet I/P uses unmodified Ethernet." I got a nice explanation from Brian Oulten (I see him often, but didn't grab a card, so I may have misspelled his name, if so, many apologies) at the recent Automation Fair. The posts, see here and here, generated some feedback in the form of comments you may want to check out. Meanwhile, not one for missing the softballs I lob at him, PTO's Carl Henning provides a lucid description of the "stack" on his blog yesterday. I wish ODVA read my blog. It could provide a little more clarity from its point of view. At any rate, the "stack" is at once a simple and a complex thing. It's simple, because there are just seven layers, of which five are commonly used, but sometimes others are bypassed as well. The more complicated issue lies at the top layer (applications) where many protocols may ride in complete standards bliss at the same time.
I guess the reason I keep coming back to this lies in my engineering roots. My first years in manufacturing required me to learn to be very precise with facts. (You can't build something if you don't know precisely what is you're building and with which materials and components.) In this battle, I keep trying to pin people down and it feels sometimes like I'm trying to grab that famous little greased pig they used to turn loose at the county fair.
11:34:55 AM 
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