rstp prp hsr

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: [email protected]

Zrcher Fachhochschule

Contents

1. Ethernet Redundancy Schemes2. Applications Requirements3. Parallel Redundancy Protocol (PRP)4. High-availability Seamless Redundancy (HSR)5. Comparison6. Reference Implementation7. Conclusions


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


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


Reconfiguration Protocols:Rapid Spanning Tree Protocolck

Ethernet withmesh topology

Ethernets forwardingmechanism requires a loopfree topology


Reconfiguration Protocols:Rapid Spanning Tree Protocolck


Reconfiguration Protocols:Media Redundancy Protocol

MRM

MRM

x


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


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


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 .


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)


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


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


ANetwork A

Network B

RedundancyManager

application

RedundancyManager

application

DAN DAN

Parallel Redundancy ProtocolNormal Operation

AA B B


A B

RedundancyManager

application

A B

RedundancyManager

application

DAN DAN

Parallel Redundancy ProtocolOperation with Fault

Network ANetwork B


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


High-availability Seamless RedundancyBasic Idea and Network Element Types


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


RedundancyManager

application

IED

IED

RedundancyManager

application

IED

IED

High-availability Seamless RedundancyNormal Operation

RedundancyManager

RedundancyManager


RedundancyManager

application

IED

IED

RedundancyManager

application

IED

IED

High-availability Seamless RedundancyOperation with Fault

RedundancyManager

RedundancyManager


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


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


High-availability Seamless RedundancyRedBox


High-availability Seamless RedundancyExtensions


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


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


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


PRP/HSR Reference Implementation


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


HSR GigE RedBoxRing Forwarding Delay (cut-through)

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

rstp prp hsr

Documents

ethernet redundancy

flavours protocols

ethernet mrp

synchronization protocols

switchover time seamless

highavailability mechanisms

independent paths

substation automation