A primary challenge for IIoT automation and control applications is the ability to efficiently and effectively collect the data that becomes the grist for IoT enterprise-level, decision making and analytics. And while a wide variety and different types of edge devices have been introduced, a major concern is how to collect data from these devices.

Several protocols have emerged that are being used for enterprise and cloud connectivity, including MQTT, AMQP and CoAP, but MQTT has emerged as the top choice for implementing IoT connectivity.

Connectivity via MQTT through a local gateway enables edge devices to communicate effectively with SCADA systems, HMIs and cloud applications. (Image source: MOXA)

In a white paper on MQTT in the IIoT era, Moxa Product Manager Chase Shih concludes that the MQTT is ideal for Internet of Things applications, and especially those that stress active notification where devices only provide data when needed.

“MQTT’s broker/client design eliminates the need for all devices in the system to be online at the same time. The clients communicate directly with the broker, which plays the role of middleman to pass messages back and forth between clients,” Shih wrote.

MQTT Protocol Advantages

MQTT uses a publish-subscribe mechanism for exchanging messages between one broker and a number of clients, who can also be either publishers or subscribers. The protocol allows developers to resolve common connection issues, and addresses the issue of devices that are not guaranteed to be on the network at the same time.

Major cloud supplier support from the likes of AWS IoT, Google Cloud and Microsoft Azure IoT Hub has helped MQTT become a dominant IoT message protocol and method for collecting the machine data that is required for companies to achieve digital transformation.

Another major advantage of the protocol is its ability to address security concerns. MQTT brokers provide support for account names and password to prevent unauthorized clients to connect and subscribe to topics. It also provides TLS encryption of data transmission to minimize data vulnerability during the transmission itself.

Arlen Nipper, president of Cirrus Link Solutions, notes that even though the protocol was developed more than 20 years ago, the MQTT specification is based on top of TCP/IP.

According to Nipper, “the issues of cybersecurity were almost non-existent in 1998, but TCP/IP has withstood the test of time and best practice security can be applied to any MQTT infrastructure. Also note that since MQTT is a “Remote Originated” TCP/IP socket connection, edge devices and application clients do not even have to have any TCP/IP ports open. This is a huge reduction in the overall cybersecurity footprint.”

MQTT Architecture

Shih notes that two major MQTT system architectures are being used, and that traditional OT applications are being refitted using the MQTT protocol. Using the protocol to connect directly to the cloud is helping to provide the benefits of cloud service hardware along with the ability to provide both non-stop service and a rich set of data mining tools.

The other option is to connect to a local gateway to collect edge device data and/or to enable machine-to-machine (MTM) communication in the field. This can potentially minimize costs by using a MQTT client to collect and send usable data to a SCADA system, HMI or cloud service.

Many challenges are still to be resolved at the application level but MQTT is clearly a megatrend in automation and control that is continuing to emerge as a way to help achieve digital transformation in smart manufacturing. Many legacy devices don’t support the protocol, and there are still integration issues with traditional IT systems. Traditional OT systems have often used Modbus, for example, but IT engineers lean toward protocols such as MQTT, RESTful API, and SNMP to collect data, and are not familiar with Modbus.

For more information on this trend, check out these resources:

• Moxa white paper: “MQTT—Enabling Edge-Device Connectivity in the IIoT Era”
• MQTT ratified by ISO/IEC: www.iso.org/standard/69466.html