# Communication Protocols of an Industrial Internet of Things Environment: A Comparative Study
## 2 Related Work  
In the context of industry, researchers are proposing and examining protocols, networks, and middleware architectures for industrial ICT infrastructure and integration.  
For integration purposes, the authors of [33] proposed a data-oriented machine-to-machine (M2M) communication middleware based on the ZeroMQ platform for IIoT applications. The researchers of [34] presented a case study for controlling industrial robots and monitoring energy consumption remotely based on Ebbits middleware, which transforms data into web services. Another service-oriented IIoT middleware is proposed in [35] for balancing task allocation between a mobile terminal and a utility cloud service. In [36], a platform based on SystemJ for IIoT is proposed using an FPGA (field programmable gate array), and then tested in an automation system. Reference [37] describes a collaboration-oriented M2M (CoM2M) messaging mechanism for IIoT, based on the platform PicknPack food packaging line. In [38], legacy flexible manufacturing systems are integrated with the SCADA system of an Industry 4.0 framework via Ethernet. However, these research papers investigated middleware architectures for integration purposes.  
The infrastructure of an IIoT was examined in [39], where the IoT vision in industrial wireless sensor networks was implemented using the IPv6 over low-power wireless personal area network (6 LoWPAN) and CoAP. Furthermore, the author of [40] proposed a software-defined network for an IIoT based on new networking technologies. However, these research papers investigated network solutions and architectures.  
Infrastructure protocols were examined in many studies. For example, the authors of [41] developed an edge IoT gateway to extend the connectivity of MODBUS devices to IoT by storing the scanned data from MODBUS devices locally, and then transferring the changes via an MQTT publisher to MQTT clients via a broker. The researchers of [42] designed and implemented a web-based real-time data monitoring system that uses MODBUS TCP communications, following which all data are displayed in a real-time chart in an Internet browser, which is refreshed at regular intervals using hypertext transfer protocol (HTTP) polling communications. In [43], a MODBUS serial protocol was reported that collects data serially via a RS-232 protocol and transfers the collected data over the ZigBee protocol. In [44], measurements of field devices collected by the MODBUS serial protocol were transferred over HTTP using a Wi-Fi network. However, these papers proposed a gateway as a bridge between MODBUS and the Internet, Intranet, or wireless network.  
In this study, the MODBUS TCP is proposed to be implemented in two scenarios--either alone, or in parallel with an MQTT publisher without a gateway. The first solution proposes the MODBUS TCP as an IoT protocol to build the industrial environment on a standalone basis. Using the second arrangement, the MODBUS TCP executes its operations while maintaining the requirements of industrial applications and MQTT achieves the M2M communications for IoT functions.