The High-Availability Seamless redundancy protocol (HSR): Robust fault-tolerant networking and loop prevention through duplicate discard

In the last decade, Ethernet technology has paved its way from the use in office environments into the world of mission-critical networks, e.g. in industrial automation and control in production environments. Recent advancements in power utility automation place Ethernet at the communication infrastructure of electrical substations. To fulfill the requirement of drop-out free fault-tolerance in this application field, new Ethernet redundancy mechanisms have been developed: HSR and PRP. These methods are usually implemented in hardware, e.g. FPGAs. Thus, several key performance characteristics of the protocol are implementation-specific and can be altered. This paper gives an overview of PRP and HSR, outlines the implications of the protocol design in hardware to physical topologies and describes how design decisions can influence protocol performance.