rstp prp hsr
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Ethernet Redundancy with zero Switchover Time
Florian Reichert, Hans Weibel
Zurich University of Applied Sciences Institute of Embedded SystemsTechnikumstrasse 9CH-8401 Winterthur
Phone: +41 58 934 75 52WWW: http://ines.zhaw.chMail: hans.weibel@zhaw.ch
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Zrcher Fachhochschule
Contents
1. Ethernet Redundancy Schemes2. Applications Requirements3. Parallel Redundancy Protocol (PRP)4. High-availability Seamless Redundancy (HSR)5. Comparison6. Reference Implementation7. Conclusions
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Institute of Embedded Systems:Who we are?
Zurich University of Applied Sciences (ZHAW) is a Swiss School of Engineering ZHAWs Institute of Embedded Systems (InES) has a strong
commitment to industrial communications in general and to Ethernet and wireless in particular, e.g. Real-time Ethernet extensions (Ethernet Powerlink, ProfiNet, etc.) Synchronization protocols (IEEE 1588) High-availability mechanisms for Ethernet (MRP, PRP, HSR, etc.) Wireless (sensor networks, low energy Bluetooth, RFID, UWB)
The related activities include Protocol stacks Hardware assistance and off-load (IP) Support, engineering, and consultancy
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Redundancy Protocols for Ethernet:Two Flavours
Protocols using reconfiguration (with small recovery time) Rapid Spanning Tree Protocol (RSTP)
IEEE 802.1D-2004IEC 62439-1 Annex A (recovery time calculation methods)
Media Redundancy Protocol (MRP) IEC 62439-2
Protocols with zero switchover time (seamless, bumpless) Parallel Redundancy Protocol (PRP)
IEC 62439-3 Clause 4 High-availability Seamless Redundancy (HSR)
IEC 62439-3 Clause 5
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Reconfiguration Protocols:Rapid Spanning Tree Protocolck
Ethernet withmesh topology
Ethernets forwardingmechanism requires a loopfree topology
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Reconfiguration Protocols:Rapid Spanning Tree Protocolck
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Reconfiguration Protocols:Rapid Spanning Tree Protocolck
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Reconfiguration Protocols:Media Redundancy Protocol
MRM
MRM
x
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Bumpless Redundancy Protocols
Basic idea multiple copies of the same frame are transmitted over independent
paths receiving node processes the frame arriving first; subsequent copies
are discarded does not only handle failures but also random frame loss
Parallel Redundancy Protocol (PRP) two independent paths provided by two networks
High-availability Seamless Redundancy (HSR) two independent paths provided by the two directions of a ring
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Availability Requirements
Three examples where uninterrupted connectivity is absolutely required:
Power utility and substation automation IEC 61850 defines applications with very short and even with zero
recovery time (see table)
Safety protocols Retransmission timeout may be shorter than network recovery time
Low latency audio and video (live events) Low latency does not allow retransmission Loss of a single frame is audible/visible and not acceptable in
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Application Example: Requirements according to IEC 61850-5 Ed2
Communicating partners
Service Application recovery tolerated delay
Required Communication Recovery Time
SCADA to IED, client-server
IEC 61850-8-1 800 ms 400 ms
IED to IED interlocking IEC 61850-8-1 12 ms (with Tmin set to 4 ms)
4 ms
IED to IED, reverse blocking
IEC 61850-8-1 12 ms (with Tmin set to 4 ms)
4 ms
Protection trip excluding Bus Bar protection
IEC 61850-8-1 8 ms 4 ms
Bus Bar protection IEC 61850-9-2on station bus
< 1 ms Bumpless
Sampled Values IEC 61850-9-2on process bus
Less then two consecutive samples
Bumpless
To fulfill these requirements, IEC 61850-8-1 and -9-2 uses redundancy solutions standardized for Industrial Ethernet by IEC 62439-3 .
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Application Example: SwitchingAudio/Video with Ethernet
Goal: Replacement of dedicated audio/videocross-point switchers with Ethernet Broadcasting stationsLive events (concerts, opera, sports, theaters)Requirements:Highly scalable design (from one up to thousands of channels)Phase locked media clocks over the networkStreaming with low latencySeamless redundancySolution: again PTP and HSR like redundancy (merging in play out buffer)
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Parallel Redundancy ProtocolBasic Idea and Network Element Types
PRP uses doubled network infrastructure
Basic redundancy function requires Doubly Attached Nodes (DAN): Same send/receive function on both ports
No forwarding between the ports Standard nodes directly attachable
but : no redundancy support no connectivity between LAN A /B
Safe discard of duplicates by redundancy trailer added to frames
Redundancy Box (RedBox) Full connectivity for Virtual Dual
Attached Nodes (VDANs) Acts as proxy node for VDANs
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Parallel Redundancy ProtocolRedundancy Control Trailer
time
destination source LT FCSLSDUpreamble LSDUsizeSeqNr
L
a
n
I
d
Redundancy Control Trailerframe without redundancy control
0 6 12 14octet position
PRPsuffix
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ANetwork A
Network B
RedundancyManager
application
RedundancyManager
application
DAN DAN
Parallel Redundancy ProtocolNormal Operation
AA B B
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A B
RedundancyManager
application
A B
RedundancyManager
application
DAN DAN
Parallel Redundancy ProtocolOperation with Fault
Network ANetwork B
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ANetwork A
Network B
RedundancyManager
application
RedundancyManager
application
DAN DAN
Parallel Redundancy Protocolwith long Delay on Network B
Memory for previously received frames required (duplicate discard buffer)
Buffer size depends on maximal difference of network delay In case of a forgotten frame the duplicate is not discarded will be
(most likely) be eliminated by upper layers
AA B B
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High-availability Seamless RedundancyBasic Idea and Network Element Types
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High-availability Seamless RedundancyHSR Tag
time
destination source LT FCSpayloadpreamble LSDUsize SeqNr
P
a
t
h
I
d
HSR tag
0 6 12 14octet position
HSR_ET
original LPDU
1816
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RedundancyManager
application
IED
IED
RedundancyManager
application
IED
IED
High-availability Seamless RedundancyNormal Operation
RedundancyManager
RedundancyManager
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RedundancyManager
application
IED
IED
RedundancyManager
application
IED
IED
High-availability Seamless RedundancyOperation with Fault
RedundancyManager
RedundancyManager
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High-availability Seamless RedundancyUnicast Traffic
end node
end node
end node
end node
end node
end node
end node
sender
receiver
A-frame B-frame
switch
RedBox
singly attached nodes
interlink
solid arrows: unicast trafficvoid arrows: not received unicast traffic
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High-availability Seamless RedundancyMulticast Traffic
end node
end node
end node
end node
end node
end node
end node
sender
receiver
A-frame B-frame
switch
RedBox
singly attached nodes
interlink
red arrows: A framesgreen arrows B framesblue arrows: non-HSR frames
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High-availability Seamless RedundancyRedBox
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High-availability Seamless RedundancyExtensions
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IED
IED
PRP/HSR in Parallel and Ring Redundancy
RedundancyManager
application
IEDRed
undanc
y
Manag
er
IED
IED
IED IED
IED
IED
application
Station BusPRP
Process BusHSR
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IEDIED
Station BusPRP
Process BusHSR
PRP/HSR in Parallel and Ring Redundancy
RedundancyManager
application
IEDRed
undanc
y
Manag
er
IED
IED
IED IED
IED
IED
application
Failure
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Redundancy ProtocolsComparison
Criteria HSR PRP RSTP MRPtype bumpless bumpless reconfiguring reconfiguringsupported topologies
ring mesh (including ring, star, chain)
mesh (including ring, star, chain)
ring
capacity to be installed
traffic volume doubled
traffic volume doubled
unused links unused link
Infra-structure
HSR switch in every ring node
switching nodes of arbitrary type
legacy managed switch
MRP switch in every ring node
Implemen-tation
HSR switching engine (FPGA)
SW sub-layer in end node
SW for standard switching chip
SW for standard switching chip
maturity products under development
in commercial use
widely used since long time
widely used in industrial networks
scalability limited by ring capacity
scales well scales well limited by ring capacity
coupling options
by RedBox and QuadBox:HSR-to-HSRHSR-to-PRPHSR-to-legacy
by RedBox:PRP-to-HSRPRP-to-legacy
n/a by MRP capable switch:MRP-to-legacy
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PRP/HSR Reference Implementation
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HSR RedBox Capabilities and Characteristics
Cut-through switching between the HSR ring ports A and B Forwarding delay between ring port A and B is about 6 us
(assuming empty queue on output port) Configurable frame buffer size and queue length Dynamic frame buffer allocation (page manager) 100 Mbit/s full-duplex Ethernet (GigE as prototype) One VLAN tag supported RedBox can manage 128 VDANs Duplicate detection per TX port with a configurable history
buffer size and aging time Synchronization according to IEEE 1588 supported
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HSR GigE RedBoxRing Forwarding Delay (cut-through)
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SIEMENS
Thanks to the HSR Project Teamfor the slides
Ethernet Redundancy with zero Switchover TimeContentsInstitute of Embedded Systems:Who we are?Redundancy Protocols for Ethernet:Two FlavoursReconfiguration Protocols:Rapid Spanning Tree ProtocolckReconfiguration Protocols:Rapid Spanning Tree ProtocolckReconfiguration Protocols:Rapid Spanning Tree ProtocolckReconfiguration Protocols:Media Redundancy ProtocolBumpless Redundancy ProtocolsAvailability RequirementsApplication Example: Requirements according to IEC 61850-5 Ed2 Application Example: Switching Audio/Video with EthernetParallel Redundancy ProtocolBasic Idea and Network Element TypesParallel Redundancy ProtocolRedundancy Control TrailerParallel Redundancy ProtocolNormal OperationParallel Redundancy ProtocolOperation with FaultParallel Redundancy Protocolwith long Delay on Network BHigh-availability Seamless RedundancyBasic Idea and Network Element TypesHigh-availability Seamless RedundancyHSR TagHigh-availability Seamless RedundancyNormal OperationHigh-availability Seamless RedundancyOperation with FaultHigh-availability Seamless RedundancyUnicast TrafficHigh-availability Seamless RedundancyMulticast TrafficHigh-availability Seamless RedundancyRedBoxHigh-availability Seamless RedundancyExtensions PRP/HSR in Parallel and Ring RedundancyPRP/HSR in Parallel and Ring RedundancyRedundancy ProtocolsComparisonPRP/HSR Reference ImplementationHSR RedBox Capabilities and CharacteristicsHSR GigE RedBox Ring Forwarding Delay (cut-through)Thanks to the HSR Project Teamfor the slides
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