Which of the following is a common industrial network protocol used in automation?

Modbus is widely recognized as a common industrial network protocol specifically designed for automation environments. It enables communication between various devices, such as sensors and controllers, within an industrial setting. Modbus operates on a master/slave architecture, which allows for data exchange over serial lines or Ethernet. Its simplicity, ease of implementation, and compatibility with a wide range of devices make it a go-to choice for factory automation, process control, and building management systems.

In contrast, HTTP (HyperText Transfer Protocol) is primarily used for transferring web pages on the internet and is not tailored for real-time control and monitoring of industrial devices. FTP (File Transfer Protocol) is designed for transferring files over a network and lacks the specific capabilities needed for industrial automation tasks. SMTP (Simple Mail Transfer Protocol) is used for sending emails and is not suitable for direct device communication in automation applications. Therefore, Modbus stands out as the most appropriate choice for industrial network communication in automation contexts.