GE Multilin F650, User Manual

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B-4 F650 Digital Bay Controller GEK-113000AE
B.1 PRP AND HSR ETHERNET PROTOCOLS APPENDIX B
B
B.1.1 PRP
PRP defines a redundancy protocol for high availability in substation automation networks. It is applicable to networks
based on Ethernet technology (ISO/IEC 8802-3).
PRP is designed to provide seamless recovery in case of a single failure in the network, by using a combination of LAN
duplication and frame duplication technique. Identical frames are sent on two completely independent networks that
connect source and destination, see next figure.
Figure B–1: EXAMPLE OF PRP REDUNDANT NETWORK
Under normal circumstances both frames will reach their destination and one of them will be sent up the OSI stack to the
destination application, while the second one will be discarded. If an error occurs in one of the networks and traffic is
prevented from flowing on that path, connectivity will still be provided through the other network to ensure continuous
communication. However, care must be taken when designing the two LANs, so that no single point of failure (such as a
common power supply) is encountered, as such scenarios can bring down both LANs simultaneously.
PRP uses specialized nodes called doubly attached nodes (DANPs) for handling the duplicated frames. DANPs devices
have an additional module at the link layer level, called the Link Redundancy Entity (LRE). LRE is responsible for
duplicating frames and adding the specific PRP trailer when sending the frames out on the LAN, as well as making
decisions on received frames as to which one is sent up the OSI stack to the application layer and which one is discarded.
In essence LRE is responsible for making PRP transparent to the higher layers of the stack. There is a second type of
specialized device used in PRP networks, called RedBox, with the role of connecting Single Attached Nodes (SANs) to a
redundant network.
F650 relays implement only the DANP functionality. The RedBox functionality is not implemented.
The original standard IEC 62439-3 (2010) was amended to align PRP with the High availability Seamless Redundancy
(HSR) protocol. To achieve this, the original PRP was modified at the cost of losing compatibility with the PRP 2010
version. The revised standard IEC 62439-3 (2012) is commonly referred to as PRP-1, while the original standard is PRP-0.
The F650 relays support only PRP-1.