Abstract
Most industrial and SCADA-like (supervisory control and data acquisition) systems use proprietary communication protocols, and hence interoperability is not fulfilled. However, the MODBUS TCP is an open de facto standard, and is used for some automation and telecontrol systems. It is based on a polling mechanism and follows the synchronous request–response pattern, as opposed to the asynchronous publish–subscribe pattern. In this study, polling-based and event-based protocols are investigated to realize an open and interoperable Industrial Internet of Things (IIoT) environment. Many Internet of Things (IoT) protocols are introduced and compared, and the message queuing telemetry transport (MQTT) is chosen as the event-based, publish–subscribe protocol. The study shows that MODBUS defines an optimized message structure in the application layer, which is dedicated to industrial applications. In addition, it shows that an event-oriented IoT protocol complements the MODBUS TCP but cannot replace it. Therefore, two scenarios are proposed to build the IIoT environment. The first scenario is to consider the MODBUS TCP as an IoT protocol, and build the environment using the MODBUS TCP on a standalone basis. The second scenario is to use MQTT in conjunction with the MODBUS TCP. The first scenario is efficient and complies with most industrial applications where the request–response pattern is needed only. If the publish–subscribe pattern is needed, the MQTT in the second scenario complements the MODBUS TCP and eliminates the need for a gateway; however, MQTT lacks interoperability. To maintain a homogeneous message structure for the entire environment, industrial data are organized using the structure of MODBUS messages, formatted in the UTF-8, and then transferred in the payload of an MQTT publish message. The open and interoperable environment can be used for Internet SCADA, Internet-based monitoring, and industrial control systems.
Highlights
The Internet of Things (IoT) is an emerging technology that represents a cost-effective, scalable, and reliable ecosystem, proposed for many applications, including smart city sectors [1,2], consumer devices [3,4], industrial environments [5,6], Internet of vehicles [7,8], multimedia [9,10], and 5G systems [11,12]
While industrial requirements of control and monitoring can be met via the MODBUS TCP using the request–response model, the message queuing and telemetry transport (MQTT) protocol complements its operation by fulfilling the IoT requirements, using the publish–subscribe pattern for M2M communications
A comparison between the MODBUS TCP and the MQTT protocol is conducted from three aspects
Summary
The Internet of Things (IoT) is an emerging technology that represents a cost-effective, scalable, and reliable ecosystem, proposed for many applications, including smart city sectors [1,2], consumer devices [3,4], industrial environments [5,6], Internet of vehicles [7,8], multimedia [9,10], and 5G systems [11,12]. Industrial Internet of Things (IIoT) [22,23], Industry 4.0 [24,25], Smart Manufacturing [26,27], and Smart Factory [28,29] are all terminologies for the emerging industrial environments that employ information and communication technologies (ICTs), including IoT platforms, while maintaining industry requirements. While industrial requirements of control and monitoring can be met via the MODBUS TCP using the request–response model, the MQTT protocol complements its operation by fulfilling the IoT requirements, using the publish–subscribe pattern for M2M communications. A second scenario is proposed here, which is to consider the MODBUS TCP as an IoT protocol, and build the IIoT environment with the MODBUS TCP only This solution is efficient and complies with most industrial applications; it only depends on the request–response model.
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