  Internet of Things (IoT) can be widely used in various applications such as
manufacturing industry,achieving high operational efficiency and increased
productivity.The exploitation of IoT paradigm made more feasible the use of
distributed control systems (DCS) where more than one PLCs implement an
industrial application.In case of having more than one PLC,it is obligatory to
ensure their inter-communication.In this paper,a solution for PLCs'
communication using Message Queuing Telemetry Transport (MQTT) IoT-protocol is
presented.An experimental industrial plant was used,controlled by two PLCs.For
the process' implementation,two Siemens gateways Simatic IoT2020 were
integrated and communicated with the PLCs through Modbus Remote Terminal Unit
(RTU) industrial protocol.Finally,data exchange between the two gateways was
established using MQTT protocol.
