The properties of IIoT (Industrial Internet ofThings) communications differ significantlyfrom more familiar control protocols, suchas EtherNet/IP, Profinet, and EtherCAT. So, howcan manufacturers assess the numerous communicationmethods available to them to take advantageof the IIoT?

The first step is realizing that IIoT and Industry4.0-based solutions require detailed data. IO-Linkis a standardized sensor interface, which providesaccess to detailed sensor/actuator data from thelowest field level, meets this requirement. Whiledigital switching sensors provide only individualbits, IO-Link provides access to detailed identification,diagnostic, and parameter data from asensor or actuator.

Next, take note of the fact that most automationsystems are based on a PLC that containsthe logic of the application. For applications suchas controlling a robot arm, sensor data needs tobe highly accurate and reliable. In a few milliseconds,the PLC calculates the output signals andtransfers them to actuators, such as valves andmotors. Control-based Ethernet protocols, suchas Profinet, EtherNet/IP, and EtherCAT, meetthese requirements.

Although these protocols are essentially basedon the Ethernet standard, specific properties havebeen changed to achieve the high degree of timingaccuracy and quick millisecond cycle times requiredin industrial applications. The data carried by theseprotocols can only be exchanged using special hardware,such as a PLC, and processed using specificsoftware offered by the control system manufacturers.But transferring data from the field level tohigher-tier systems, such as cloud-based systems,is a basic requirement for IIoT.

OPC UA, MQTT,and REST APIsThis is where IIoT communications such as OPCUA, MQTT, and REST APIs come in. These communicationmethods rely less on real time data inthe millisecond range and more on end-to-enddata availability across different systems fromdifferent manufacturers. IIoT is not about theindividual process data of sensors and actuators,but rather about the overall picture. The mostimportant process may be collecting conditiondata to avoid any future failures or detectingcorrelations in process parameters that have aninfluence on product quality. In these operations,real time is not a top priority.

OPC UA is an entire framework with sophisticatedsecurity mechanisms. A key advantageof OPC UA is that no specific device descriptionfiles are required. Each individual device has allthe necessary data, such as its own data structure,in a format that can be read by both people andmachines. OPC UA is especially suitable for largerIIoT projects, where devices from different manufacturersmust be combined but the network canstill be dimensioned accordingly.

While OPC UA largely operates using client/server connections, MQTT is based on the publish/subscribe mechanism (note: OPC UA alsonow supports publish/subscribe, though mostexisting installations usethe traditional client/server method). In publish/subscribe, a publisher(data provider) provides itsdata to a centrally locatedserver (often referred to asa broker) on the network.Subscribers (data consumers)can flexibly subscribeto all the publishers dataor to individually selectedtopics. Since there is nopermanent connectionbetween the publisherand each subscriber, thedata overhead for MQTTis significantly lower. Thismakes MQTT especiallysuitable in networks with limited availability orwhen information must be transmitted to severalconsumers at the same time.

An API (application programming interface)is a programming interface provided on a device.REST stands for Representational State Transferand outlines the conditions for designing the API.A REST API allows customers to create theirown applications based on the device data, wherebasic conditions are defined without obligation.The APIs for an organizations own devices arestandardized within that organization. This makesREST APIs especially suitable for applicationswhere many different devices from the samemanufacturer are used.

The key difference between IIoT communicationsand control network protocols is that IIoTcommunication methods were designed to allowfor an end-to-end and transparent data flow fromthe sensor to the cloud, enabling the huge potentialof Industry 4.0 and IIoT.

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How Network Communications Drive the IIoT Revolution - Automation World