Redundancy Concepts in Profinet

CTE is constantly working to increase the availability of our customers' systems. Ethernet-based communication systems are therefore primarily used for high-availability systems. These offer several advantages: Not only can system availability be made more dynamic with different redundancy options, but the systems are also faster.

In automation systems, fieldbuses are an essential element for the communication of various components with a control system. Due to the ever-increasing demands on their availability and speed, serial fieldbuses such as Profibus are increasingly reaching their limits. For this reason, they are gradually being replaced by Industrial Ethernet-based systems. These provide greater flexibility in the connection and offer an increased transfer speed of up to 1 Gbit per second. This flexibility means that the system can be equipped with different redundancy options depending on the availability requirements.

The three most important factors for Industrial Ethernet systems are controller redundancy, network redundancy, and logical redundancy within the software. There are many options available on the market for Industrial Ethernet solutions. One that has established itself in the European market is Profinet. The Profibus & Profinet International Group (PI) Profinet was launched as early as 2003 as an alternative to Profibus. Initially, however, this new standard was slow to gain traction. In recent years, the technical advantages of Ethernet-based solutions, as well as the growing portfolio of supported hardware, Profinet has made it one of the market leaders in Europe. Profinet also offers many advantages in terms of availability.

Four System Redundancy Topologies

1. S1 System Redundancy	Here, the IO devices are connected to the controller without any redundancies. An interruption in the communication connection leads to a failure of the components.
2. S2 System Redundancy	This involves controller redundancy in combination with logical redundancy on the component side. These are connected to the controllers in an open ring. If the primary controller fails or communication is interrupted, the secondary controller is automatically activated and all components establish the connection individually. However, if an interface module fails, the component fails completely.
3. R1 System Redundancy	This is a combination of controller and network redundancy. Each component is connected to a controller via two interface modules. Compared to system redundancy S2, the system differs in that it has two separate networks, thus offering protection against a network failure. If an interface module fails, the component is still available. The disadvantage of this solution is the double volume of cables used.
4. R2 System Redundancy	R2 redundancy is a combination of S2 and R1 redundancy. Accordingly, both logical and physical redundancy is provided on the controller and component side. This structure means that a fault can occur at network and controller level without affecting the functionality of the system.
5. Media Redundancy Protocol	In addition to the system redundancies, Profinet supports the media redundancy protocol (MRP), which ensures availability through a ring topology. MRP is a logical redundancy. A ring master blocks one port of the ring and communicates with all IO devices via the other. If the master loses the connection to one or more IO devices due to a wire break or failure of an IO device, the second port is released and communication is re-established via it.

Conclusion

Profinet supports many standardized methods for implementing system redundancy. Furthermore, these can be freely combined to provide additional safeguards for critical applications. However, it is important to note that not all connection options and protocols are available on all control systems and devices. Therefore, this must be clarified in each case before the system topology is defined, and the system must be adapted accordingly.

CTE is currently working on extending Profinet support to additional control systems, with the goal of enhancing safety in our customers’ high-availability systems.

Redundancy Concepts in Profinet

Four System Redundancy Topologies

Conclusion

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