Siemens RUGGEDCOM ROX II, User Manual

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Chapter 14
Network Redundancy
RUGGEDCOM ROX II
CLI User Guide
658 Parallel Redundancy Protocol (PRP)
Redundant Network Access (RNA) provides instead hitless network recovery by deploying the Parallel Redundany
Protocol (PRP).
CONTENTS
• Section 14.4.1.1, “Parallel Redundancy Protocol (PRP)”
• Section 14.4.1.2, “Supervision Frames”
• Section 14.4.1.3, “PRP Requirements”
Section 14.4.1.1
Parallel Redundancy Protocol (PRP)
Defined by the IEC 62439-3 standard, the Parallel Redundancy Protocol (PRP) replicates each data packet over
two physically independent Ethernet networks (LAN A and LAN B) to guarantee the delivery of at least one of the
packets should one network fail.
In a PRP redundant network, there are
Double Attached Nodes (DANs) , Singly Attached Nodes (SANs) , Virtual
DANs (VDANs) and RedBox devices.
• DANs
Double Attached Nodes (DANs) are PRP-aware devices that have a network port connected to LAN A and
and a network port connected to LAN B. DANs duplicate each received data packet and assign them both
a Redundancy Check Trailer (RCT) before sending them simultaneously to their destination nodes. An RCT
contains a sequence number that helps the destination node identify which packets are duplicates. Destination
nodes remove the RCT from the first packet they receive and then consume them. If a second packet is received,
the destination node knows to discard it.
• SANs
Singly Attached Nodes (SANs) are PRP-unaware devices connected to either LAN A or LAN B.
• RedBox
RedBox devices, or PRP Redundancy Boxes, function similarly to DANs, except they also act as proxies on behalf
of other devices that are PRP-unaware and have only one network port.
• VDANs
A Virtual DAN (VDAN) is any device that sits behind a RedBox. While these devices are unable to connect directly
to the redundant network like other PRP-aware devices, they can function like a DAN through the RedBox.
In a PRP redundant network, RUGGEDCOM MX5000 and MX5000RE devices are configured as RedBox devices.