OPC UA Scalability

I’ll admit it. I’m often confused. Many things I see and read confuse me. For example, I don’t understand why I am the only one in the airport, rental car, bus, or plane who isn’t holding onto their cell phone like it’s their most important possession. I see people who pay more attention to their phone then they do to their oxygen tank. Seems to me that the tank’s a bit more important. I also don’t understand why a guy would walk around with his drawers below his butt cheeks. Isn’t that uncomfortable? And I don’t understand pancakes with strawberries and cream on top. It’s either dessert or breakfast. Not both! I don’t get it.

In the technology realm, OPC UA, from the OPC Foundation, is confusing. It took me quite a few months to wrap my head around it because it’s just so different from everything else I’ve ever experienced. I can understand why most people are confused by it. It’s why I get questions like “How much is OPC UA?” That question is very much like asking the GM dealer “how much is one of you vehicles?” OPC UA is sort of like a car lot. A great deal of variety and many options.

OPC UA is a very flexible and scalable protocol. EtherNet/IP and all the rest are anything but scalable. They have a fixed transport, a fixed encoding, a fixed application API – everything is fixed. If you want to build an EtherNet/IP Adapter, you’ll need n bytes of Flash and n bytes of RAM to get it done. There is no variability. It’s the same for ProfiNet IO, Modbus TCP, DeviceNet, and Profibus.

Scalability was built into OPC UA from the start. Small pieces of functionality called Conformance Units are combined to form OPC UA devices with varying capabilities. Combining the minimum set of conformance units together forms an OPC UA device that operates with minimum functionality and minimum resources – exactly what you need for low end devices.

These levels of device capability are called Profiles. A Nano profile device is a device containing the minimum set of conformance units. A Nano profile, at least the one from our company, requires as little as 16K of RAM and 60K of Flash. But the Nano profile is not for everybody. It does not include security, publish–subscribe functionality and any additional transports.

As you add more conformance units, the capabilities of an OPC UA device get more sophisticated. Adding conformance units for security and publish–subscribe, you get the Micro profile. That profile has more capabilities but requires a larger footprint than the Nano profile. And even more capabilities and resources are required for the Embedded and Standard Servers.

It is this capability to support devices with different resource constraints that makes OPC UA so scalable. It is also what makes OPC UA so difficult for users to understand. They are not used to devices that can be scaled. So many device vendors ask for OPC UA without understanding that they really need to understand their platform, the different OPC UA profiles, and the use cases for their device.

There’s an awful lot more to think about when talking about deploying OPC UA devices. And that’s what creates all the confusion. Luckily, I can help you with OPC UA. I have two books on the subject:

One little one that’s a quick overview OPC UA Overview for those of us who are not Networking Gurus

And one with a lot more detail
OPC UA – Unified Architecture: The Everyman’s Guide to the Most Important Information Technology in Industrial Automation

Let me know how you like them. An amazon review would be nice, but I don’t want to hear from you if you’re a devotee of pancakes and cream. I’ll just never understand that.