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Telegrams in industrial communication

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. 

Technical basics

In industrial communication, the term "telegram" typically refers to a structured data packet used for transmitting information between devices and systems within automation environments. The operation of telegrams involves several key mechanisms as follow: 

Telegram structure

A telegram consists of several components that work together to ensure the accurate delivery and interpretation of data. In the context of an automation system, a telegram is composed of datagrams, which are smaller units of data associated with each network component. When a telegram is transmitted, it includes datagrams for each of the network components it passes through. A sample structure consists of the following: 

  • Header: Contains control information such as the source address, destination address, and type of message. 
  • Payload: This is the actual data content, which is made up of datagrams corresponding to specific network components. 
  • Footer: Often includes error-detection information like checksums or cyclic redundancy checks (CRC) to ensure data integrity during transmission. 

Data encoding

Information is encoded into electrical signals, typically as pulses, which represent binary code consisting of zeros and ones. In traditional settings, Morse code was used by telegraph operators to encode text messages.  

Network topologies: 

The transmission of telegrams in industrial environments is carefully orchestrated to minimize delays and prevent data loss. Telegrams are transmitted through a network of interconnected components that can be arranged in different network topologies, such as ring, linear, or hierarchical structures. 

  • Ring structure: In this arrangement, network components are connected in a loop. Telegrams are propagated around the ring, and each component removes its datagram and appends a new one, if necessary, before passing the telegram to the next component. 
  • Linear structure: Here, components are connected in a line, with telegrams traveling from one end of the line to the other and back. Like the ring structure, each component updates its portion of the telegram as it passes through. 
  • Star structure: This is a type of network configuration where each device is connected to a central hub or switch, which acts as a conduit for transmitting data. This topology offers simplicity in design and ease of troubleshooting, as well as enhanced performance by isolating each connection to the central point. 

Error checking methods

Error detection and correction are crucial for maintaining data integrity in industrial communications. Common techniques used include parity bits, checksums, and cyclic redundancy checks (CRC). Below are the primary methods utilized: 

  • Parity Check: Involves adding a parity bit to the data to make the number of ones either even (even parity) or odd (odd parity). If the parity condition is not met at the receiving end, an error is detected. 
  • Checksum: A checksum is a calculated value based on the sum of the bits in the data segment. Both the sender and receiver calculate this value and compare it to detect errors. 
  • CRC (Cyclic Redundancy Check): This method uses polynomial division to generate a code based on the data packet's contents. The receiver performs the same division, and if the resulting code matches, the data is considered valid. CRC is highly effective at detecting common types of errors in digital data. 

Advantages of telegram-based communication

Telegram-based communication offers several advantages in industrial settings, making it a preferred choice for data exchange and control within automation environments. Here are the key advantages of using telegram in industrial communication: 

  • Structured data transmission 

Telegrams define a standardized format for data exchange, including headers for addressing, function codes for operations, and data fields. This structured approach ensures clarity, consistency, and interoperability across different devices and protocols. 

  • Efficient and optimized communication 

Telegrams are designed to optimize data transmission efficiency. They use compact binary encoding or ASCII format to minimize bandwidth usage and reduce transmission overhead, which is crucial for maintaining high-performance industrial network. 

  • Real-time and deterministic communication 

Many industrial protocols based on telegram communication support real-time and deterministic data exchange. This capability is essential for time-sensitive applications where precise timing and synchronization are required, such as control systems in manufacturing or process automation. 

  • Reliability and error detection 

Telegrams incorporate error-checking mechanisms such as checksums or cyclic redundancy checks (CRC). These mechanisms ensure data integrity by detecting and correcting transmission errors, thereby enhancing the reliability of data exchange in industrial environments. 

  • Scalability and flexibility 

Telegram-based protocols offer scalability to accommodate growing network sizes and complexity. They support various communication modes (cyclic, acyclic, isochronous) and network topologies, providing flexibility in system design and integration. 

Industrial communication with Hilscher

As a leading company in the field of industrial communication, Hilscher offers a broad portfolio of technologies and solutions for networking industrial environments. 

This includes a wide range of interface solutions for connecting sensors, actuators and controllers to industrial communication networks. The communication controllers of the netX family form the basis for this. The multiprotocol-capable SoCs can be integrated into automation components as required and their extensive chip peripherals enable powerful, efficient and flexible solutions. A protocol change is achieved by simply reloading Hilscher's own netX firmware. Building on this, the company also offers embedded modules and PC cards in all form factors in order to realize the netX communication interface with less integration effort. 

Hilscher also offers a comprehensive managed industrial IoT range under the netFIELD brand. This ranges from edge gateways as an application-oriented computer platform with integrated container management and the Edge OS Runtime running on it to the central cloud portal, via which the docker containers are deployed to the edge devices, through to turnkey containers for communication applications. 

Gateways and switches, devices for network diagnostics as well as masters and bridges for the wireless connection of IO-Link sensors round off the automation portfolio. 

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