Parallel Redundancy Protocol

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The Parallel Redundancy Protocol (PRP) describes a redundant data communication network. It has been standardized in the IEC 62439-3 standard "Industrial communication networks: high availability automation networks" since 2010. It is a Layer 2 redundancy procedure, which is independent of higher layers and is intended to be suitable for the real-time Ethernet mechanisms described in IEC 61784 . PRP was developed for automation networks that require high availability for continuous operational functionality.

While reconfiguration-based redundancy protocols such as RSTP or MRP always require a certain switchover time for a new configuration in the event of errors in the network, the PRP protocol offers smooth, continuous operation in the event of an error in one of the two redundant networks, in which no data packet is lost or delayed during transmission.

topology

  • PRP network

  • PRP package format (with trailer)

  • PRP node (DANP) interaction

Each PRP node, a so-called "Dual Attached Node" (DAN) is connected to two networks, LAN A and LAN B here. Since PRP is a Layer 2 protocol, the protocol of the two networks must be identical on the MAC level. The topology, performance and latency can be different for both networks, but the latencies may only differ up to a certain limit, since PRP is a sliding window protocol based on packet sequence numbers with finite window capacity. The networks must be designed so that they fail independently of one another. If a cable is pulled in one network, the other must not be affected. In principle, there must therefore be no direct connection between the two LANs.

Switching on a "Single Attached Node" (SAN), d. H. An end node without PRP capability can be implemented using a so-called "Redundancy Box" (RedBox), which behaves like a DAN on the parallel redundant network.

An interesting application can be found in the field of wireless communication as a " timing combiner " with which the availability of a wireless " black channel " can be improved, for example for security applications .

Individual evidence

  1. ↑ Vogel Business Media GmbH & Co. KG: Page 2: Properties of the IEC 62439-3 PRP protocol . ( vogel.de [accessed on January 7, 2018]).
  2. ↑ H. Kirrmann, M. Hansson, P. Muri: IEC 62439 PRP: Bumpless recovery for highly available, hard real-time industrial networks . In: 2007 IEEE Conference on Emerging Technologies and Factory Automation (EFTA 2007) . September 2007, p. 1396-1399 , doi : 10.1109 / EFTA.2007.4416946 ( ieee.org [accessed January 7, 2018]).

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