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Seamless Redundancy with PRP and HSR

The Parallel Redundancy Protocol (PRP) and the High-Availability Seamless Redundancy Protocol (HSR) enable completely uninterrupted handling of single network failures (cables, power supply, switches, etc.) and are standardized by the International Electrotechnical Commission (IEC) as IEC 62439-3.

Parallel Redundancy Protocol

For PRP, two completely independent networks are operated in parallel (LAN_A and LAN_B). Connected high-availability Dual Attached Nodes (DANs) have two network ports, one connected to LAN_A and the second connected to LAN_B. The topology of the networks can be freely selected, disjunct cable routing is advantageous. Both LAN_A and LAN_B can even be operated with other redundancy concepts within the LANs themselves.

All packets are always sent via both connections to both LANs. The receiver accepts the packets on both ports and ignores the packet arriving later.

PRP can be implemented in an additional software layer or as an upstream hardware solution (RedBox). The redundancy concept therefore requires no switching or reconfiguration.

DAN: Dual Attached Node Implementing PRP, high-availability node with two network interfaces
SAN: Single Attached Node, standard node with a single network interface
RedBox: Redundancy Box
VDAN: Virtual Dual Attached Node

A Redundancy Box (RedBox) connects normal nodes, i.e. those with only one network interface, to both LANs of a PRP network. Because such a node appears to other nodes (DAN) as a node with two interfaces, they are called Virtual Dual Attached Nodes (VDAN).

The processes of duplicating the packets and filtering out the duplicates are performed in the RedBox. The processes are completely transparent to the VDANs, i.e. the RedBox takes over all PRP functions of the connected nodes. Particularly, it also sends the necessary supervision packets.

For network management, the RedBox can also appear as an independent DAN with its own IP address and provide corresponding functions.

High-Availability Seamless Redundancy Protocol

With the HSR protocol, seamless redundancy is achieved not by two completely separate networks, but by simultaneous transmission in both directions on a closed ring.
The HSR concept includes the following network elements and options (see figure):

InES implemented different solutions for redundancy, please get in touch with us if you are interested!