PROFINET or Ethernet in Montreal?

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I’m just back from a week in Canada where we held PROFINET one-day training classes in Toronto and Montreal.  I was really pleased by the engagement of the attendees in both cities.  They asked really good questions.  Here are a couple questions from Montreal:

“Where should we use PROFINET instead of Ethernet?”

“Tell me about limitations – distance limitations, number of devices per network.”

PROFINET or Ethernet?

First, please recognize that Ethernet is not a protocol; it’s just layers 1 and 2 of the ISO stack.  I explained that situation in a previous post called “Why Use Industrial Ethernet?” (Check the links there, too.)  Some Industrial Ethernet protocols try to use TCP or UDP plus IP to transfer real-time data; PROFINET does not.  When they try to do that, they introduce jitter and time delays.  (See the Industrial Ethernet Book article: “Technical Article: Performance metrics for Industrial Ethernet”.)  So, use PROFINET when you need low-jitter, real-time data and as a bonus you get additional diagnostics plus the ability to do peer-to-peer integration, vertical integration, functional safety, motion control, and more.


Distance limitations for PROFINET are the same as for regular Ethernet.  That’s 100 meters for copper, longer for fiber.  Wireless Ethernet distance limitations for PROFINET are the same as regular wireless, too.  For WiFi that’s 30-100 meters and for Bluetooth 10-100 meters.  But there are some caveats: crowded wireless spectrum, impenetrable objects, and more.  Talk to your wireless products vendor and get their advice about your individual situation.

How many devices per network?  There are no theoretical limitations.  But as Yogi Berra said “In theory there is no difference between theory and practice. In practice there is.”  For practical purposes the controller will have a limit on the number of nodes it can handle.  The number of available addresses in the system’s subnet will also be a limit.  Even these practical limits are not likely to limit even a large system though.

Other points from the Course Evaluations:

“I enjoyed how the questions were handled.  Also how you changed presenters regularly.”

“Best organized seminar I’ve attended! Thanks.”

“Really great, not a vendor speech.”  [We make it that way on purpose. It helps that as a non-profit trade organization we have nothing to sell.]

“In greater detail: security, network sniffing.”  [Due to time constraints, we have to draw the line at some level of detail, so we leave the network sniffing for the Certified Network Engineer class.  For security we provide a list of resources including the PROFINET Security Guideline.]

More classes are still to come, including tomorrow’s PROFIBUS one-day training class in Baltimore.

–Carl Henning

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