PRP can be implemented entirely in software, i.e.Nodes with single attachment can be attached to one network only.
This is in contrast to the companion standard HSR (IEC 62439-3 Clause 5), with which PRP shares the operating principle. They have been adopted for substation automation in the framework of IEC 61850. For such applications, the recovery time of commonly used protocols such as the Rapid Spanning Tree Protocol (RSTP) is too long. Cost impact is low since it makes little difference if the spares lie on the shelf or are actually working in the plant. The maintenance interval is shortened since more components can fail in use, but such outage will remain invisible to the application. The two LANs have no links connecting them and are assumed to be fail-independent, to avoid common mode failures. The two frames travel through their respective LANs until they reach a destination node (DANP) with a certain time skew. The destination node accepts the first frame of a pair and discards the second (if it arrives). Therefore, as long as one LAN is operational, the destination application always receives one frame. PRP provides zero-time recovery and allows to check the redundancy continuously to detect lurking failures. The sequence number, the frame size, the path identifier and an Ethertype are appended just before the Ethernet checksum in a 6-octet PRP trailer. This trailer is ignored (considered as padding) by all nodes that are unaware of the PRP protocol, and therefore these singly attached nodes (SAN) can operate in the same network. Therefore, PRP is a layer 2 redundancy, which allows higher layer network protocols to operate without modification. ![]() Also, delay measurement messages (PdelayReq PdelayResp) are not duplicated since they are link-local. A slave will normally listen to one port and supervise the other, rather than switching back and forth or using both Syncs. This gave a good error detection coverage but difficulted the transition from PRP to the High-availability Seamless Redundancy (HSR) protocol, which uses a ring topology instead of parallel networks. This allowed building transparent PRP-HSR connection bridges and nodes that can operate both as PRP (DANP) and HSR (DANH). Selecting a Standard Redundancy Method for Highly Available Industrial Networks, 2006 IEEE International Workshop on Factory Communication Systems, 27 June 2006 Page(s):386 390. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.
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