For decades now, industrial networks in their various fieldbus and Ethernet forms have handled all the communication between the controllers, devices and any of the various nodes that exist on the network. And while these networks will continue to do what they’ve always done for the some time to come, there is a change brewing on the network communications horizon.
Though there is no shortage of possibilities surrounding how various IT data communication methods could come into play in the industrial arena, the two technologies angling for greater prominence today are MQTT and RESTful APIs (see links at the bottom of this article for other Automation World coverage of these technologies). With so much activity going on in this area, I asked Opto 22’s Matt Newton to clarify the difference between RESTful APIs and MQTT.
“RESTful APIs and MQTT are complementary technologies,” said Newton. “MQTT is designed to move data efficiently between different nodes on a network. RESTful APIs are designed to move data efficiently between different software applications on those nodes.”
Newton explained that RESTful APIs are application programming interfaces that conform to the REST architectural style of software development. “For example, Opto 22’s RESTful API defines exactly how a software application should format a data request to our controller’s RESTful HTTP/S server to read the status of an I/O point or control system variable and move it directly into a database,” he said.
MQTT differs in that it is “a protocol designed to move data more efficiently from one node to another in networks where connectivity is unreliable or bandwidth is at a premium,” said Newton. “MQTT is preferred in these types of applications for its minimal packet overhead and publish/subscribe (pub/sub) architecture.”
Noting that both technologies provide benefits for automation applications at different levels, Newton explained that RESTful APIs allow software developers to leverage existing APIs available from thousands of software applications—both on-premise and cloud-based—along with control system data; MQTT allows older poll/response mechanisms to be augmented or replaced with efficient pub/sub mechanisms.”
One of the concepts I have often heard discussed is that technologies like RESTful APIs and MQTT could do away with the need for gateways to connect legacy industrial technologies to the Internet. When I asked Newton about this, he said that the promise of these technologies is not so much to eliminate the need for gateways, as it is to reduce the need for gateways, protocol converters and middleware.
“Like we saw with Ethernet as it moved into the automation space, moving technologies like RESTful APIs and MQTT down to the lowest levels increases data availability, reduces complexity, eases maintainability and lowers costs,” said Newton. “And though new sensors and devices are being developed that embed Industrial Internet of Things (IIoT) connectivity technologies, there is a huge number of legacy sensors and devices already in place. That’s why we chose to build RESTful APIs and web transport protocols into our industrial controllers so that automation professionals don’t have to buy new sensors and devices to realize the potential of the IIoT.”
Newton contends the ongoing communication transformation in automation comes down to the “dollars-and-cents return on investment. In many cases, gateways and converters are not already installed, because the ROI wasn’t there if costly middleware systems had to be used to get the data. Now, RESTful APIs make the process much simpler and less expensive, opening up vast new areas where the data can be used. When the costs of obtaining data go down, people will find many more uses for much more types of data.”
Recent Automation World coverage of IT technologies and industrial control: