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Ethernet is not a Protocol

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Bryon Sol

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Not that long ago, Ethernet wasn’t common on PLCs and other industrial devices.  Even 10 years ago you often had to buy a separate option card to add Ethernet to your PLC.  But now it has become ubiquitous and with it has come a plethora of terminology and misunderstanding.

I often hear customers ask, “does this PLC support Ethernet communications?” Unfortunately, the answer for most current PLCs is yes.  Why is this an unfortunate answer? The problem is Ethernet is not a communications standard, and it is not even a hardware standard. 

So, what is Ethernet and what do I mean when I say that it is not a Protocol?  Simply put Ethernet is a family of computer networking technologies (Wikipedia, 2020).  This can be comprised of various hardware, firmware and software technologies working together to provide communications between devices.

To explain Ethernet, let’s look at an analogy and use Telephones as our example.

In the early days, we had simple devices and a switchboard operated by people.  The main components haven’t changed much but the technology certainly has.  We still have the receiver (the telephone), the wires and some type of switchboard.  This is the hardware layer. 

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On top of the hardware we now have firmware – our cordless phones in our house have firmware to talk to the base station for instance and the switchboard is something we don’t even worry about anymore.  We just accept that the hardware and firmware do what we need it to do.

Similarly, with Ethernet we have a hardware layer.  This consists of the physical devices such as PLCs, HMIs, Robots, etc., cables and Ethernet switches.

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The technology has moved from a computer-based communications standard to communications for all sorts of things such as IIoT, Smart Home devices, and so much more.

So, coming back to the original statement “Ethernet is not a Protocol”, what does that mean? It means that we still have not discussed the signals going over those wires and how they are formed and how the devices on each end of the line process them. 

Imagine for a second hearing your phone ring, picking it up and the person on the other end starts speaking a foreign language and you do not understand them.  At a very high level you could consider that a PROTOCOL.  They are using the same hardware as you, they are sending data and receiving data, but the two of you are not talking the same language so you can’t communicate with each other.

In and Industrial environment, there are a lot of protocols that have been developed by different companies over the years, some of the most common are:

  • Modbust/TCP – Developed by Modicon (now Schneider Electric)
  • MC Protocol – Developed by Mitsubishi Electric
  • PROFINET – Developed by Siemens
  • EtherCAT – Developed by Beckhoff Automation
  • Ethernet/IP – Developed by Rockwell Automation (Allen-Bradley)

There are many more out there, and there are even variations within protocols by certain vendors depending on the hardware platform.  For instance, most Rockwell PLCs can talk Ethernet/IP but some will only do a subset called Explicit messaging and will not perform Implicit messaging.

Of course, this matters a lot, because while we may be able to physically connect all of the components on the same network, they may not be able to communicate with each other.

So the next time you are trying to choose hardware for a project, the question you should be asking is not “what communications hardware” does this device have, which is what you are asking when you ask if a device has Ethernet.  Instead ask “what protocols is this device capable of using” – or in other words, what languages does it talk. 

Once all of our devices are talking the same language, system deployment time and development time can be significantly reduced and you will know that you have a rock solid and stable platform.

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