What is a Node?

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One of the questions that came up in the market share discussion over at Gary Mintchell’s Feed Forward blog (Ethernet in Manufacturing and Automation) centered on the definition of a node.  Thanks to a telephone conversation with the author of the study that sparked it all, John Morse of IMS Research, I can answer some of that.

First of all, IMS also recognizes the difficulty in defining a node.  They’ve settled on this definition in their report:

A network node is defined as a single connection to a network, regardless of the number of other connections to that node. Only nodes that are permanently connected to a network in order to add data to or retrieve data from the network are considered. Simple I/O switches and communication ports used for programming and set-up are not considered to be nodes on the network.

They enumerate 16 devices including controllers, IO modules, drives, vision systems, and the like.  They do not include infrastructure components like Ethernet switches.

The calculation for the node counts starts with shipments and subtracts devices not using the capability and devices going out of service.

Their node count does not include wireless nodes; they have a separate report for those.

My reaction to this new information:
1. I wish their definition said “Ethernet switches” instead of “I/O switches” since I think that’s what they mean.
2. Because there are wireless nodes of PROFINET from a number of vendors, we may be underrepresented in this report.
3. I miss the good old days when we could just count chips like we do for PROFIBUS.

Since PROFINET uses standard Ethernet, standard Ethernet controller chips can be used.  (I blogged about that recently in “PROFINET Uses Standard Ethernet!”)  Some Industrial Ethernets do always use a chip; and if the chip goes in every IO module, counting those chips would give an apples-to-oranges comparison with other Industrial Ethernets.  For example, PROFINET counts the overall IO device, not the individual IO modules.

In the end, I am very confident in our procedure for counting PROFINET nodes using an independent, third party auditor.  I still don’t know how or what other Industrial Ethernets count.

–Carl Henning

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