A telegram is widely understood to be the telegraphic transmission of messages using acoustic, optical or electrical devices, which became popular as the first means of synchronous communication over long distances in the 19th century. However, a telegram in the sense of digital data processing is different. Data telegrams or datagrams are standardized data records that are transmitted digitally and used for control purposes in system automation.
Data telegrams play a central role in industrial communication, i.e. the exchange of data between the countless components of modern automation systems. These are structured data packets that are transmitted precisely and promptly between devices such as controllers, sensors and actuators. Industrial communication protocols define the rules and standards for processing and exchanging data telegrams between devices.
In industrial communication, there is a whole range of communication protocols that were originally developed by different companies and are now being further developed by independent organizations. The common protocols and technologies can generally be divided into three classes.
Fieldbus protocols have been specially developed for industrial automation and enable communication between controllers and decentralized field devices. Examples of this are PROFIBUS, Modbus and CANopen, both of which use robust error detection mechanisms such as CRC and offer deterministic real-time communication. These protocols are often found in networked production units, where they ensure reliable data transmission and system control.
Industrial Ethernet protocols use Ethernet technology to enable a higher data rate and greater range. Typical representatives of these protocols are Ethernet/IP, EtherCAT and PROFINET. They are based on the TCP/IP standards and offer extended error correction and synchronization mechanisms. These protocols are designed to integrate seamlessly into existing IT infrastructures, making them ideal for use in modern, networked factories.
IIoT (Industrial Internet of Things) protocols are designed to meet the requirements of networked Industry 4.0. Examples include MQTT and OPC UA, which are specifically designed to transfer data across large networks with minimal overhead. They allow sensors, actuators and other devices to be integrated into a global network, enabling seamless data analysis and process optimization in real time. These protocols are characterized by their scalability and their ability to securely transmit large amounts of data.
