With the advent of Industry 4.0, there is an increasing demand for intelligence, automation and digitization in manufacturing. In this context, the Modbus protocol faces some challenges:

• Firstly, the Modbus protocol has significant security issues. Its straightforward communication method renders it susceptible to security risks, including hacking attacks and data tampering.
• Secondly, when it comes to real-time performance and bandwidth utilization, the Modbus protocol falls short in comparison to modern industrial communication standards. Especially in the case of large-scale device networking, traditional serial communication methods are no longer sufficient to meet requirements.
• In addition, in terms of multi-level architecture and cloud platform applications, the Modbus protocol also has certain limitations. It can only perform point-to-point communication and does not support distributed systems and cloud computing platforms very well.

Compared with Modbus protocol, the MQTT protocol has obvious advantages. The MQTT protocol is a lightweight message transmission protocol based on publish/subscribe model that is built on TCP/IP protocol. It was released by IBM in 1999 and became an officially approved communication standard by OASIS in 2014. Currently it has been widely applied in areas such as Internet of Things (IoT), mobile internet, smart hardware, connected cars, smart cities, remote healthcare services, power industry, oil and energy.

Here are some of the advantages of MQTT.

• Lightweight: MQTT is very lightweight and can be used in environments with limited bandwidth and poor network quality.
• Flexibility: MQTT supports multiple connection methods and enables flexible message transmission through the subscribe/publish model.
• Reliability: MQTT ensures reliable message transmission, even in case of network interruption, by allowing reconnection and communication restoration.
• Security: MQTT supports SSL/TLS encryption and authentication mechanisms to ensure data security.

Therefore, in the field of IoT, MQTT is more suitable for message transmission in distributed systems.