Discover the essential network architectures for Industry 4.0: focus on redundancy, MRP and PRP protocols to ensure seamless availability.
In the world of automation and connected factories, network reliability is no longer an option, but a vital necessity. Unlike office computer networks (IT), where a brief outage of a few seconds is often tolerable, an industrial network (OT) supports critical processes. A loss of communication can lead to production line shutdown, costly material damage, or even human safety risks.
The Challenge of Industrial Redundancy
The standard protocol used in the computer world to avoid network loops is the [Spanning Tree Protocol (STP)](https://en.wikipedia.org/wiki/Spanning_Tree_Protocol). However, the convergence time of STP (the time required to find a new path in case of failure) is counted in seconds. In industrial environments, this delay is unacceptable. Robust topologies aim for two main objectives:
Industrial Ring and MRP Protocol (IEC 62439-2)
The ring topology is one of the most common configurations in factories. It allows several switches to be connected in a circular manner. To avoid broadcast storms, the [Media Redundancy Protocol (MRP)](https://www.profibus.com/technology/profinet/) is used.
The operation of MRP relies on a ring manager (Media Redundancy Manager - MRM) that logically blocks one of the ring segments to avoid loops. In the event of a physical cable break, the MRM detects the failure and unlocks the backup segment.
Seamless Redundancy: PRP and HSR
For ultra-critical applications like power distribution (IEC 61850 standard) or high-speed motion control, even 10ms of downtime is too much. This is where active redundancy protocols come in.
Parallel Redundancy Protocol (PRP)
The [PRP (IEC 62439-3)](https://en.wikipedia.org/wiki/Parallel_Redundancy_Protocol) works by duplicating packets. The source device sends two identical copies of each frame over two independent networks (LAN A and LAN B). The recipient receives the first frame to arrive and rejects the second.
High-availability Seamless Redundancy (HSR)
HSR is the cousin of PRP, but optimized for a ring topology. Each frame is sent simultaneously in both directions of the ring. If a link fails, the message still arrives through the other side of the loop, without any software reconfiguration time.
Technical Comparison: Which Topology to Choose?
The choice depends on the cost/criticality ratio of your installation:
Best Practices and Common Mistakes
The implementation of these technologies requires particular rigor. Here are the points of vigilance identified by OT network experts:
Conclusion
The robustness of an industrial network relies on its ability to survive the unexpected. While MRP remains the de facto standard for its simplicity and controlled cost, the emergence of PRP and HSR meets the requirements of absolute availability of modern critical infrastructures. Before any deployment, an impact analysis on the cycle time of your automation systems is essential to choose the suitable protocol.