As industries continue to embrace automation and digitization, the need for efficient and reliable communication networks becomes increasingly vital. PROFINET, an industrial standard running primarily on Ethernet, has emerged as a leading solution for real-time data exchange in industrial applications. It is an open standard specified by Profibus International, the organization behind the hugely successful fieldbus protocol – Profibus. It is standardized as IEC 61158 and IEC 61784, with different levels of real time behavior that can run on from basic Ethernet network to the time sensitive networks with dedicated bandwidth. At the application level, it offers different profiles that can be used for different applications/industries.
Being a very wide topic, we will cover PROFINET at a high level with an overview of the following topics, leaving the details for later articles.
- PROFINET Mapping to OSI Layer model
- Various communication types in PROFINET – Standard, RT, IRT and TSN
- Different data transfer types supported – Cyclic, Acyclic, diagnostics
- Device Types – IO Controller, Device and Supervisor
- Conformance classes and Application Profiles
Understanding the PROFINET Mapping to OSI Model
The Open Systems Interconnection (OSI) model provides a framework for understanding and implementing network protocols. We can map the PROFINET to the various layers of the OSI model as follows.
PROFINET Mapping to OSI Layer model
As can be seen, the PROFINET primarily works over the TCP/IP layer. For the standard operations this should suffice, but for the special case of real time operations it bypasses the TCP/IP layer at layers 3 and 4, layer 2 data is directly sent to the application layer. As the TCP/IP layer is well known, we will touch up on only the physical and application layers.
Physical Layer of PROFINET
The primary and most used physical connectivity for PROFINET is the copper-based Ethernet cable. Though the regular ‘IT’ Ethernet cable can be used, it is essential to use the ruggedized industrial Ethernet cable for reliability and handle challenges specific to OT environments. In addition to that, PROFINET also supports fiber optic cables for wired connectivity. For wireless, it can be supported over Bluetooth or Wi-Fi. The choice of media depends on factors such as distance, noise immunity, and bandwidth requirements.
PROFINET supports various types of connectors, such as RJ45, M12, and fiber optic connectors. These connectors can be chosen based on the application requirements to ensure a reliable connection between devices.
Exploring PROFINET RT (Real Time)
As mentioned earlier, for standard uses PROFINET packets go through the TCP/IP layer or UDP/IP layers to ensure reliable delivery. But in many cases real-time communication is crucial in industrial applications where timely data exchange is essential. The inherent latencies in the TCP/IP protocol, makes it unsuitable for this purpose. To overcome this limitation, PROFINET offers real-time capabilities through PROFINET RT (Real Time). PROFINET RT ensures deterministic data transmission, enabling precise control and synchronization of devices.
PROFINET RT achieves real-time communication by utilizing specific protocols and mechanisms that prioritize time-critical data. While running on Ethernet, it leverages the EtherType field in the frame and by having a value of 0x8892, it enables the lower layer to directly deliver the frame to the application layer reducing latency. This ensures that data packets are delivered within very short time intervals, guaranteeing the responsiveness and reliability required in industrial environments.
PROFINET Isochronous Real Time (PROFINET IRT)
PROFINET Isochronous Real Time (PROFINET IRT) is an extension of PROFINET RT that provides enhanced real-time capabilities. PROFINET IRT is specifically designed for applications with extremely time-critical requirements, such as motion control systems.
PROFINET IRT achieves ultra-low latency and jitter by utilizing dedicated communication channels and time slots. By improving the Ethernet performance using specific rules to switch PROFINET traffic and setting aside a dedicated bandwidth, it effectively reduces collisions. This ensures precise and deterministic data transmission, enabling seamless coordination of devices in high-performance industrial applications with cycle times in the range of 31.25 us.
PROFINET over TSN (Time Sensitive Networking)
With the advent of Time Sensitive Networking (TSN), PROFINET has extended its capabilities even further. PROFINET over TSN combines the benefits of PROFINET with the deterministic and time-aware features of TSN.
TSN enables the convergence of various industrial Ethernet protocols on a single network infrastructure, ensuring seamless communication between devices from different vendors. With features of dedicated streams, time synchronization with precise clocks, scheduled traffic, pre-emptive frames and redundancy, PROFINET over TSN offers enhanced interoperability and flexibility, making it a future-proof solution for industrial networks.
PROFINET Cyclic Data Exchange
Cyclic data exchange is a fundamental feature of PROFINET that enables the continuous and periodic exchange of data between devices. PROFINET utilizes cyclic communication to ensure real-time control and monitoring of industrial processes.
In cyclic data exchange, devices exchange data packets at predefined intervals, allowing for precise synchronization and coordination over the TCP/IP. This ensures that devices are updated with the latest information in a timely manner, enabling seamless operation and control.
PROFINET Acyclic Data Exchange
In addition to cyclic data exchange, PROFINET also supports acyclic data exchange. Acyclic data exchange enables devices to exchange data on an event-driven basis, rather than at predefined intervals. This allows for flexible and on-demand communication between devices, catering to non-real-time requirements.
Acyclic data exchange, typically run on the UDP/IP protocol, is particularly useful for configuration, diagnostics, and parameterization of devices. It provides a mechanism for devices to exchange information when needed, ensuring efficient management and maintenance of the industrial network.
PROFINET Device/Network Diagnostics
Maintaining and troubleshooting industrial networks can be challenging, especially in large-scale installations. PROFINET provides comprehensive diagnostic capabilities to facilitate the identification and resolution of issues.
PROFINET devices and network components incorporate diagnostic alarms and functionalities that enable real-time monitoring and reporting of network health. This allows for proactive maintenance and rapid troubleshooting, minimizing downtime and ensuring optimal performance.
PROFINET Device Classification - IO-Controllers, IO-Devices, and IO-Supervisor
PROFINET devices are classified into three categories: IO-Controllers, IO-Devices, and IO-Supervisors. Each category serves a specific role in the PROFINET architecture and has distinct functionalities.
IO-Controllers are responsible for controlling and coordinating IO-Devices within the network. They provide the intelligence and decision-making capabilities required for efficient industrial automation. Examples include PLCs, SCADA, Control Applications, HMIs etc.
IO-Devices, on the other hand, are the physical devices that interact with industrial processes, such as sensors and actuators. They typically send/receive cyclic data with the measured/set values and acyclic alarm/diagnostic data as needed. IO-Supervisors, as the name suggests, supervise and monitor the network, ensuring its stability and performance. They can perform diagnostic operations and help identify and trouble shoot network problems.
PROFINET Conformance Classes
To ensure interoperability and compatibility between PROFINET devices, the PROFINET standard defines different conformance classes. These conformance classes specify the required features and functionalities that devices must adhere to.
The conformance classes range from Class A to Class D, with Class D being the most advanced and feature rich. Class A devices support basic cyclic and acyclic data communication whereas Class D supports isochronous data transfer leveraging the TSN Ethernet networking. The implementation complexity and certification efforts also increase based on the conformance class. Class A devices are used for infrastructure and building automation, Class B for factory and process automation, with class C and D for highly critical motion control applications.
PROFINET Application Profiles
PROFINET supports various application profiles that define specific requirements and functionalities for different industrial applications. Application profiles provide a standardized approach to implementing PROFINET in specific domains, such as process automation or motion control. As we have seen earlier on Profibus application profiles, both General and Specific application profiles are available. Some of the profiles include PROFIsafe, PROFIdrive, PROFIenergy. These profiles define the necessary parameters, communication modes, and device interactions for specific application scenarios.
GSD (General Station Description) is a standardized format used in PROFINET to describe the capabilities and characteristics of devices. GSD files provide essential information about devices, such as supported communication protocols, IO channels, and diagnostic capabilities.
Conclusion
PROFINET, as an industrial Ethernet standard, offers a comprehensive and reliable solution for real-time data exchange in industrial applications. With a few million devices in the field, PROFINET is undoubtedly one of the most popular industrial automation protocols. By understanding the various aspects and functionalities of PROFINET, one can have a good visibility on the industrial networks, ensuring seamless communication and efficient automation.
While an in-depth introduction has provided you with a solid foundation to understand PROFINET, upcoming articles will cover each of these sections in detail.
