A.1 Background

Modbus was first introduced by Modicon® (now part of Schneider Electric®) for process control systems. It is used to establish master-slave/client-server communication between intelligent devices and sensors and instruments. It is a de facto standard, truly open and the most widely used network protocol in the industrial manufacturing environment.

Modbus is easy to deploy and maintain and is used across a wide range of industries. It is also an ideal protocol for Remote Terminal Unit (RTU) applications where wireless communication is required. Modbus is not only an industrial protocol. Building, infrastructure, transportation and energy applications also make use of its benefits.

Originally, Modbus was implemented as an application level protocol intended to transfer data over serial port, it has expanded to include implementations over serial, TCP/IP, and UDP. Today, it is a common protocol used by countless devices for simple, reliable, and efficient communication across a variety of networks. Modbus was designed as a request-response protocol with a flexible data and function model that are part of the reason it is still in use today. In addition, support for the simple and elegant structure of Modbus continues to grow [i.4].