3 TelecomProfileFrequency Syncan May 2012

7/28/2019 3 TelecomProfileFrequency Syncan May 2012

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ThePTPTelecomProfileforFrequency

Synchronization

ConfidentialCopyright2012

TimFrost(presentedbyLeeCosart)

May23,2012

PTP(PrecisionTimeProtocol)Defined

TheNatureofPacketTiming

Agenda

FrequencySync ron zat onArc tecture

G.803ReferenceChain

PacketTimingArchitecture

ThePTPTelecomProfile(G.8265.1)

ObjectivesandDesignFeatures

SourceTraceabilit

2ConfidentialCopyright2012

Multicastvs.

Unicast messages

RateofTimingMessages

MasterSelectionandProtection


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PTP(PrecisionTimeProtocol)Defined


WhatisthePrecisionTimeProtocol(PTP)?

ProtocolSpecificationfordistributingprecisetimeandfrequencyoverpacketnetworks

Firstversion(2002)targetedLANapplications

Secondversion(2008)expandedapplicabilitytocovertelecommunicationsnetworks

TimeiscarriedineventmessagestransmittedfromaGrandmasterClocktoa

SlaveClock


Runs

over

Ethernet

and/or

IP

networksCommonlyreferredtoas:

PTP(PrecisionTimeProtocol)orPTPv.2

IEEE15882008orIEEE1588v.2


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WhatisaPTPProfile?

Whatisaprofile?

ProfileswereintroducedinIEEE15882008,toallowotherstandards

Profilescontainadefinedcombinationofoptionsandattributevalues,aimedatsupportingagivenapplication

Allowsinteroperabilitybetweenequipmentdesignedforthatpurpose

PTPTelecomProfileforFrequency(G.8265.1)publishedOct.2010


uppor s requencysync ron za onover e ecomne wor s

Main

use

case

is

the

synchronization

of

cellular

base

stations

TheG.8265.1PTPTelecomProfileenablesthedeploymentof

PTPbasedsynchronizationbytelecomoperators

TheNatureofPacketTiming



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Conventionaltimingsignal:

Anominallyperiodicsignal,generatedbyaclock:

WhatisaPacketTimingSignal?

Conventionaltimingsignal:

Anominallyperiodicsignal,generatedbyaclock:Si nificant instants

Packettimingsignal:

A nominall eriodic si nal enerated b a acket master clock:

Timingjitterandwander


PacketDelay

Variation

Payload4 HPayload4 H Payload4 HPayload4 H Payload4 HPayload4 H Payload4 HPayload4 H

Packets(header,payloadandfooter)

Payload4 HF Payload3 HF Payload2 HF Payload1 HF

Significantinstants

UseofTimestamps

Packettimingsignal:

Asequenceoftimedevents,generatedbyapacketmasterclock:

TS=8 HF TS=4 HF TS=1 HF

gn cant nstants

Packetscontainingtimestamps


123456789

Reconstructedfrequency:


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PrecisionTimeProtocol(PTP)

PTPdefinesanexchangeoftimedmessagesoverapacketnetwork

Each event message flow (sync,Master Clock Time Slave Clock Time

Sync message

t2

t1

Delay_Req message t3

_

Master frequency determined bycomparison of timestamps in the eventmessage flows

e.g. comparison oft1 to t2 over multiplesync messages, or t3 to t4 indelay_reqmessages

Time offset calculation requires all fourtimestamps:

Follow_Up messagecontaining accuratevalue oft1(if required)

Data atSlave Clock

(t1), t2

t1, t2, t3

t1, t2


t4

Slave time o set =(t1 t2) + (t4 t3)

assumes symmetrical delays(i.e. the forward path delay is equal to the

reverse path delay)

Time offseterror=fwd. delay rev. delay

2

2time

Delay_Resp messagecontaining value oft4

t1, t2, t3, t4

FrequencySynchronizationArchitecture



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FrequencySynchronizationArchitecture

SSUk1PRC SSU1 SSUkChainofupto

*

Chainofupto*

Chainofupto*

NE

G.803SynchronizationReferenceChain:

s s s

SSUk1PRC SSU1 SSUkChainofupto

20EECs*MixedChainof upto

20SECs&EECs*MixedChainofupto

20SECs&EECs*NE

G.8261ModifiedReferenceChaintoincludeSynchronousEthernetClocks(EEC):

G.8261ModifiedReferenceChaintoincludePacketBasedTiming:

11ConfidentialCopyright2012* MaximumnumberofSECsorEECsintotalchain=60 MaximumnumberofSSUs(k)intotalchain =10

SSUk1PRC SSU1 SSUk

SM

Chainof

up

to

20EECs*Mixed

Chain

of

up

to20SECs&EECs*NE

Packet

Network

PTPMaster

and

Slave

connected

bypacketnetwork

SSUk1PRC SSU1 SSUk

SM

Chainofupto

20EECs*MixedChainof up

to20SECs&EECs*NE

Packet

Network

PTPMasterandSlaveconnected

bypacketnetwork

PRCPRC

GeneralPacketTimingArchitecture

PacketTimingArchitecture(G.8265)

PacketNetworkTimingProtection

PTP

GM

PTP

Primary

PTPGMPTP

GM

PTP

Primary

PTPGM

Physicallayer

syncnetwork

PTPTimingFlows PTPTimingFlows

Protection

Timin Flows

PTP

GM

PRC

Secondary

PTP GM


Slave

PTP

SlavePTP

Slave

PacketNetwork

Slave

PTP

SlavePTP

Slave

PacketNetwork


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ThePTPTelecomProfileforFrequency(G.8265.1)


PrimeObjectives

TopermitthedistributionoffrequencyusingPTPoverexistingmanaged,widearea,packetbasedtelecomnetworks

(suchasSyncE andSDH)

Todefinemessageratesandparametervaluesconsistentwithfrequencydistributiontotherequiredperformancefortelecom

applications

Toallowthesynchronizationnetworktobedesignedand


con gure na xe arrangement

Toenableprotectionschemestobeconstructedinaccordancewithstandardtelecomnetworkpractices


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Keydesigndecisions

Noonpathsupport,(e.g.boundaryandtransparentclocks),becausethesearenotgenerallyavailableinexistingnetworks

,

thanoperationoverEthernetorotherlowerlayerprotocols

ThePTPAnnounce messagewasadaptedtocarrytheQualityLevel(QL)indicationsdefinedinG.781,forcontinuitywith

SONET/SDHandSyncE synchronizationstatusmessaging.

Unicast transmissionwasadoptedovermulticast,sinceitcould


eguarantee towor overw eareate ecomsnetwor s

BMCA(Best

Master

Clock

Algorithm)

was

replaced

by

static

provisioning,allowingthesynchronizationflowtobeplanned,

ratherthandynamicallyadjustingitself

SourceTraceability

EncodesQLvaluesintheclockClass fieldoftheAnnounce message

Providesendtoendtraceabilityofthereferencesourcealongthe

Informstheslaveclock(andsubsequentdevices)ofthequalityofthetimingsource

Allowsthetimingchaintobemanagedinasimilarwaytoexistingsynchronizationnetworks

EndtoEndSourceTraceability


SSM:QLPRC[0010] clockClass:QLPRC[84]

PRC

PTP

GM

End

Equipment

PTP

Grandmaster

PacketNetworkPhysicalLayer

Synchronization Network

PTPSlave

PTP

Slave

SSM:QLPRC


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SSMQLvaluetoPTPclockClass Mapping

SSMQLvalue

ITUTG.781Network OptionsPTPclockClass

valueOptionI(2Mhierarchy)

OptionII(1.5Mhierarchy)

OptionIII(6.3Mhierarchy)

0001 QLPRS 80

0000 QLSTU QLUNK 82

0010 QLPRC 84

0111 QLST2 86

0011 88

0100 QLSSUA QLTNC 90

0101 92

0110 94

1000 QLSSUB 96

decreasing

quality,

increasing

clockClass


1 1

1101 QLST3E 100

1010 QLST3/QLEEC2 102

1011 QLSEC/QLEEC1 QLSEC 104

1100 QLSMC 106

1110 QLPROV 108

1111 QLDNU QLDUS 110

Multicastvs.Unicast

Unicast facilitatestheuseofdistributedmasters

EachmasterslavecommunicationpathbecomesaseparatePTP

Allowseasierplanningofthesynchronizationnetwork

Redundancystrategycanbecarefullymanaged

Unicast packetspropagateuniformlythroughthenetwork

Multicastrequirespacketreplicationateachswitchorrouter

Replicationprocessaddsvariabledelay


Multicast

harder

to

provision

for

network

operators Upstreammulticastoftennotsupportedintelecomnetworks


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UnicastRegistration

MasteronlyprovidesUnicast service

Nomulticastannouncemessagessent

Slaveismanuall confi uredwiththeIP

Master Slave

addressofoneormoremasters

SlaverequestsMastertoprovideunicastserviceataspecifiedrate

RequestsAnnounce servicefirst,toverifyqualityofthemaster

Ifwithincapacitylimits,Masterrespondswithservicegrantacknowledgements


SlaverequestsSyncandDelay_Request

serviceonly

ifmaster

quality

is

sufficient

Grantsarelimitedduration

Requestsmustbeperiodicallyrepeated

Freesupmasterresourcesifslavefails

RateofTimingMessages

Therateoftimingmessagesrequiredisdependentonseveralfactors

Amountofnoiseinthenetwork

Efficiencyofclockservoalgorithm

TheTelecomProfiledefinestherangeofmessageratesMastersandSlavesshouldsupport

Messagerates Minimum Maximum Default

Announce 1msg.every 16s 8messages/s 1msg.every2s

S nc 1ms .ever 16s 128messa es s Notdefined


Itisnotexpectedthataslavewillachievetherequiredperformanceatallmessagerates

Slavemustrequestthemessageratesneededtomaintainperformance

Delay_Request 1msg.

every 16s 128

messages/s Not

defined


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PacketTimingSignalFail

Profiledefinesthreetypesofsignalfailure:

PTSFlossAnnounce,wherethePTPSlaveisnolongerreceiving

Thismeansthereisnotraceabilityinformationforthatmaster

SlaveshouldswitchtoanalternativeGMafterasuitabletimeoutperiod

PTSFlossSync,wherethePTPSlaveisnolongerreceivingtimingmessagesfromtheGM(i.e.SyncorDelay_Response messages)

Thismeansthereisnotiminginformationforthatmaster


PTSFunusable,wherethePTPSlaveisreceivingtiming messagesfromtheGM,butisunabletorecovertheclockfrequency

Thismeansthereisnorecoverabletiminginformationforthatmaster

Actionisundefined

Telecomslaveclockconsistsofseverallogicalprotocolinstances,eachcommunicatingwithadifferentgrandmaster

Selection rocess follows G.781 selection rules:

MasterSelectionandProtection

Availability,Traceability,Priority

Telecom

SlaveClockPTPGM

1

Slave

Protocol

Instance1

Slave

G.781

based


2

PTPGM

N

Protocol

Instance2

Slave

Protocol

InstanceN

Master

Selection

Process

Network

ListofN

Grandmasters

SeparatePTPdomains


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AdditionalProtectionFunctions

Nonreversionfunction

Bydefault,aslaveshouldswitchbacktotheoriginalmasteronce

Optionally,thisautomaticreversionfunctioncanbedisabled

WaittoRestoreTime

Followsaninitialprotectionswitch,e.g.duetolossoftraceabilityorsignalfailure

Timewaitedbeforeswitchingbacktotheoriginalhighestpriority


mas er,once e a urecon on as eenrec e

Implies

slaves

must

continually

monitor

the

original

master

followingaprotectionswitch

AdditionalTraceabilityFunctions

Forcedtraceability

IfthePTPGMisconnectedtoareferencebyasignalwithnoSSMQLvalue,thein utcanbemanuall forcedtoasuitablevalue

OutputQLHoldOff

AppliestoslaveoutputtimingsignalsthatcarryanSSMQLvalue(e.g.SyncE)

ChangeofQLintheincomingPTPclockClass inputshouldbedelayedbeforebeingappliedtotheoutput

Allowstimeforsynchronizationtoanewreference

Avoidsanyunecessary switchingindownstreamequipment


Output

Squelch OutputclocksignalofaPTPslaveshouldbesquelchedincaseofholdover

Preventsendequipmentattemptingtosynchronizetoaclockinholdover

OnlyappliestosignalsthatdonotcarryaQLvalue(e.g.a2.048MHz

unframedtimingsignal)


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ForFurtherReading

WhitePaper:

SynchronizationforNextGenerationNetworks ThePTPTelecomProfile,Symmetricom WhitePaper,June2011

IEEEStandardforaPrecisionClockSynchronizationProtocolforNetworkedMeasurementandControlSystems,IEEEStd.1588TM2008,24July2008

PrecisionTimeProtocolTelecomProfileforFrequencySynchronization,ITUTRecommendationG.8265.1,October2010

BackgroundReading:

SynchronizationLayerFunctions,ITUTRecommendationG.781,August2008

ArchitectureofTransportNetworksbasedontheSynchronousDigitalHierarchy(SDH),


. ,

Definitionsandterminologyforsynchronizationinpacketnetworks,ITUT

RecommendationG.8260,

August

2010

TimingandsynchronizationAspectsinPacketNetworks,ITUTRecommendationG.8261,April2008

ArchitectureandRequirementsforPacketBasedFrequencyDelivery,ITUTRecommendation G.8265,October2010

ThankYou

SeniorTechnologist,

Symmetricom,Inc.

Email:[email protected]


Symmetricom,Inc.

2300OrchardParkway

SanJose,CA951311017

Tel:+14084287907

Fax:+14084286960

www.symmetricom.com

3 TelecomProfileFrequency Syncan May 2012

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