5-46 C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUALPRODUCT SETUP CHAPTER 5: SETTINGS5If the receiving interface does not support the Far-End Fault feature or has it disabled, an incoming Far-End Fault pattern isignored.It is strongly recommended to have switches used for substation automation that support the Far-End Fault feature,especially when UR 7 redundancy Failover is selected for redundancy.5.3.5.6 Parallel Redundancy Protocol (PRP)The Parallel Redundancy Protocol (PRP) defines a redundancy protocol for high availability in substation automationnetworks. It applies to networks based on Ethernet technology (ISO/IEC 8802-3) and is based on the second edition (July2012) of IEC 62439-3, clause 4.PRP is designed to provide seamless recovery in case of a single failure in the network, by using a combination of LANduplication and frame duplication. Identical frames are sent on two completely independent networks that connect sourceand destination. Under normal circumstances both frames reach the destination and one of them is sent up the OSI stackto the destination application, while the second one is discarded. If an error occurs in one of the networks and traffic isprevented from flowing on that path, connectivity is provided through the other network to ensure continuouscommunication. Take care when designing the two LANs, so that no single point of failure (such as a common powersupply) is encountered, as such scenarios can bring down both LANs simultaneously.Figure 5-16: Example of parallel redundant networkPRP uses specialized nodes called doubly attached nodes (DANPs) for handling the duplicated frames. DANP devices havean additional module, called a Link Redundancy Entity (LRE). LRE is responsible for duplicating frames and adding thespecific PRP trailer when sending the frames out on the LAN, as well as making decisions on received frames as to whichone is sent up the OSI stack to the application layer and which one is discarded. LRE is responsible for making PRPtransparent to the higher layers of the stack.In addition, there is a second type of specialized device used in PRP networks, called RedBox, with the role of connectingSingle Attached Nodes (SANs) to a redundant network.UR relays implement 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. Therevised standard IEC 62439-3 (2012) is commonly referred to as PRP-1, while the original standard is PRP-0. The UR relayssupport PRP-1.The relay implements PRP on two of its Ethernet ports, specifically Ports 2 and 3 of the CPU module. Use the previoussection (network port configuration) to configure PRP.PRP is purchased as a separate option. If purchased (valid order code), PRP can be enabled in configuration through asetting available on the network configuration menu, REDUNDANCY, which already has the capability of enabling failoverredundancy. The options on this setting must be changed to accommodate two types of redundancy: failover and PRP.When REDUNDANCY is set to either failover or PRP, the ports dedicated for PRP (Ports 2 and 3) operate in redundant mode.In this mode, Port 3 uses the MAC, IP address, and mask of Port 2.The C70 is provided with optional PRP capability. This feature is specified as a software option at the time ofordering. See the Order Codes section in chapter 2 for details.
