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SR3 SERIES PROTECTIVE RELAY PLATFORM – COMMUNICATIONS GUIDE
350 REDUNDANCY OPTIONS
CHAPTER 3: ETHERNET INTERFACE
Figure 3-1: Example of PRP with two LANs (LAN A and LAN B)
The two LANs, named LAN_A and LAN_B, are identical in protocol at the MAC level, but
they can differ in performance and topology. Transmission delays can also be different.
The LANs have no direct connection among them and they are assumed to be fail-
independent.
In some applications, only availability-critical nodes need a double attachment, while
others do not. In order to meet the specific requirements, PRP defines different kinds of
end nodes.
•
The Dual Attached Node (DAN) is connected to both LANs.
•
Uncritical nodes can be attached to only one LAN and are therefore called Single
Attached Nodes (SAN). SANs that need to communicate with each other are on the
same LAN.
•
The Redundancy Box (RedBox) is used when a single interface node has to be
attached to both networks. Such a node can communicate with all other nodes. Since
a node behind a RedBox appears for other nodes like a DAN, it is called Virtual DANs
(VDAN). The RedBox itself is a DAN and acts as a proxy on behalf of its VDANs. The
RedBox has its own IP address for management purposes
Similarly to PRP, HSR is based in the duplication of every frame sent, but in a ring topology.
Each copy of the frame is injected in a different direction of the ring. If any of the links
between nodes is down, all nodes are still reachable. This topology forces every node in
the net to be HSR aware because they have to forward every message until it reaches its
destination. With that purpose, the redundancy information is located at the beginning of
the frame allowing a faster forwarding, see next figure.
Figure 3-2: Example of HSR with HSR Ring
Definitions
•
PRP – Parallel Redundancy Protocol - redundancy protocol for high availability in
substation automation networks based on IEC 62439-3 Clause 4 and applicable to
networks based on Ethernet technology (ISO/IEC 8802-3).
•
OSI - Open Systems Interconnection - model defined by the International
Organization for Standardization (ISO) for standardizing the functions of a
communication system in terms of abstraction layers. Similar communication
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