network card, printers, and IEDs with one network card are singly attached nodes. A SAN behind a RedBox
appears like a DAN so is called a Virtual DAN (VDAN).
VDAN
VDAN
VDAN
REDUNDANCY
BOX
SAN SAN
SAN
DAN
DAN
DAN
LAN A
LAN B
E01028
Figure 58: Example PRP redundant network
In a DAN, both ports share the same MAC address so it does not affect the way devices talk to each other in
an Ethernet network (Address Resolution Protocol at layer 2). Every data frame is seen by both ports.
When a DAN sends a frame of data, the frame is duplicated on both ports and therefore on both LAN
segments. This provides a redundant path for the data frame if one of the segments fails. Under normal
conditions, both LAN segments are working and each port receives identical frames. There are two ways of
handling this: Duplicate Accept and Duplicate Discard.
The Alstom Grid RedBox is the H382 switch. This is compatible with any other vendor's PRP device.
MiCOM P747 Chapter 8 - Redundant Ethernet
P747-TM-EN-1 245
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