High Availability Seamless Redundancy Protocol (HSR) applies the principle of parallel operation to a ring interconnecting IEDs with two links. HSR relies on ring topology, sending data not over two networks but in both directions of the single ring. High availability seamless redundancy (HSR) is a further development of the PRP approach, although HSR functions primarily as a protocol for creating media redundancy while PRP creates network redundancy. PRP and HSR are both described in the IEC 62439 3 standard.
The new PRP (Parallel Redundancy Protocol) and HSR (High-availability Seamless Redundancy) protocols are two newly developed redundancy methods that significantly increase the availability and reliability of network connections.