G704同步帧结构.docx

G704同步帧结构.docx

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G704同步帧结构

INTERNATIONALTELECOMMUNICATIONUNION

CCITTG.704

THEINTERNATIONAL

TELEGRAPHANDTELEPHONE

CONSULTATIVECOMMITTEE

GENERALASPECTSOFDIGITAL

TRANSMISSIONSYSTEMS;

TERMINALEQUIPMENTS

SYNCHRONOUSFRAMESTRUCTURES

USEDATPRIMARYAND

SECONDARYHIERARCHICALLEVELS

RecommendationG.704

Geneva,1991

FOREWORD

TheCCITT（theInternationalTelegraphandTelephoneConsultativeCommittee）isapermanentorganoftheInternationalTelecommunicationUnion（ITU）.CCITTisresponsibleforstudyingtechnical,operatingandtariffquestionsandissuingRecommendationsonthemwithaviewtostandardizingtelecommunicationsonaworldwidebasis.

ThePlenaryAssemblyofCCITTwhichmeetseveryfouryears,establishesthetopicsforstudyandapprovesRecommendationspreparedbyitsStudyGroups.TheapprovalofRecommendationsbythemembersofCCITTbetweenPlenaryAssembliesiscoveredbytheprocedurelaiddowninCCITTResolutionNo.2（Melbourne,1988）.

RecommendationG.704waspreparedbyStudyGroupXVIIIandwasapprovedundertheResolutionNo.2procedureonthe5thofApril1991.

___________________

CCITTNOTES

1）InthisRecommendation,theexpression“Administration”isusedforbrevitytoindicatebothatelecommunicationAdministrationandarecognizedprivateoperatingagency.

2）AlistofabbreviationsusedinthisRecommendationcanbefoundinAnnexB.

©  ITU  1991

Allrightsreserved.Nopartofthispublicationmaybereproducedorutilizedinanyformorbyanymeans,electronicormechanical,includingphotocopyingandmicrofilm,withoutpermissioninwritingfromtheITU.

RecommendationG.704

SYNCHRONOUSFRAMESTRUCTURESUSEDAT

PRIMARYANDSECONDARYHIERARCHICALLEVELS

（Malaga-Torremolinos,1984;amendedatMelbourne,1988,revised1990）

1General

ThisRecommendationgivesfunctionalcharacteristicsofinterfacesassociatedwith:

–networknodes,inparticular,synchronousdigitalmultiplexequipmentanddigitalexchangesinIDNsfortelephonyandISDNs,and

–PCMmultiplexingequipment.

Section2dealswithbasicframestructures,includingdetailsofframelength,framealignmentsignals,cyclicredundancycheck（CRC）proceduresandotherbasicinformation.

Sections3to6containmorespecificinformationabouthowcertainchannelsat64kbit/sandatotherbitratesareaccomodatedwithinthebasicframestructuresdescribedin§2.

ElectricalcharacteristicsfortheseinterfacesaredefinedinRecommendationG.703.

Note1–ThisRecommendationdoesnotnecessarilyapplytothosecaseswherethesignalsthatcrosstheinterfacesaredevotedtonon-switchedconnections,suchasthoseforthetransportofencodedwidebandsignals（e.g.broadcastTVsignalsormultiplexedsound-programmesignalswhichneednotbeindividuallyroutedviatheISDN）,seealsoAnnexAtoRecommendationG.702.

Note2–TheframestructuresrecommendedinthisRecommendationdonotapplytocertainmaintenancesignals,suchastheall1ssignalstransmittedduringfaultconditionsorothersignalstransmittedduringout-of-serviceconditions.

Note3–FramestructuresassociatedwithdigitalmultiplexingequipmentsusingjustificationarecoveredineachcorrespondingequipmentRecommendation.

Note4–Inclusionofchannelstructuresatotherbitratesthan64kbit/sisamatterforfurtherstudy.RecommendationsG.761andG.763dealingwiththecharacteristicsofPCM/ADPCMtranscodingequipmentcontaininformationaboutchannelstructuresat32kbit/s.Themoregeneraluseofthoseparticularstructuresisasubjectoffurtherstudy.

2Basicframestructures

2.1Basicframestructureat1544kbit/s

2.1.1Framelength:

193bits,numbered1to193.Theframerepetitionrateis8000Hz.

2.1.2F-bit

ThefirstbitofaframeisdesignatedanF-bit,andisusedforsuchpurposesasframealignment,performancemonitoringandprovidingadatalink.

2.1.3AllocationofF-bit

TwoalternativemethodsasgiveninTables1/G.704and2/G.704forallocationofF-bitsarerecommended.

TABLE1/G.704

Multiframestructureforthe24framemultiframe

F-bit

Bitnumber（s）ineachchanneltimeslot

Signallingchannel

Framenumber

withinmultiframe

Bitnumberwithin

Assignments

designationa）

multiframe

FAS

DL

CRC

Forcharactersignala）

For

signallinga）

01

1

–

m

–

1-8

–

02

194

–

–

e1

1-8

–

03

387

–

m

–

1-8

–

04

580

0

–

–

1-8

–

05

773

–

m

–

1-8

–

06

966

–

–

e2

1-7

8

A

07

1159

–

m

–

1-8

–

08

1352

0

–

–

1-8

–

09

1545

–

m

–

1-8

–

10

1738

–

–

e3

1-8

–

11

1931

–

m

–

1-8

–

12

2124

1

–

–

1-7

8

B

13

2317

–

m

–

1-8

–

14

2510

–

–

e4

1-8

–

15

2703

–

m

–

1-8

–

16

2896

0

–

–

1-8

–

17

3089

–

m

–

1-8

–

18

3282

–

–

e5

1-7

8

C

19

3475

–

m

–

1-8

–

20

3668

1

–

–

1-8

–

21

3861

–

m

–

1-8

–

22

4054

–

–

e6

1-8

–

23

4247

–

m

–

1-8

–

24

4440

1

–

–

1-7

8

D

FASFramealignmentsignal（...001011...）.

DL4kbit/sdatalink（messagebitsm）.

CRCCRC-6blockcheckfield（checkbitse1ae6）.

a）Onlyapplicableinthecaseofchannelassociatedsignalling（see§3.1.3.2）.

TABLE2/G.704

AllocationofF-bitsforthe12-framemultiframe

Framenumber

Framealignmentsignal

Multiframealignmentsignal

orsignalling

1

1

–

2

–

S

3

0

–

4

–

S

Note–Formultiframestructure,see§3.1.3.2.2.

2.1.3.1Method1:

Twenty-four-framemultiframe

AllocationoftheF-bittothemultiframealignmentsignal,theCRCcheckbitsandthedatalinkisgiveninTable1/G.704.

2.1.3.1.1Multiframealignmentsignal

TheF-bitofeveryfourthframeformsthepattern001011...001011.Thismultiframealignmentsignalisusedtoidentifywhereeachparticularframeislocatedwithinthemultiframeinordertoextractthecyclicredundancycheckcode,CRC-6,andthedatalinkinformation,aswellastoidentifythoseframesthatcontainsignalling（frames6,12,18and24）,ifchannelassociatedsignallingisused.

2.1.3.1.2Cyclicredundancycheck（CRC）

TheCRC-6isamethodofperformancemonitoringthatiscontainedwithintheF-bitpositionofframes2,6,10,1418and22ofeverymultiframe（seeTable1/G.704）.

TheCRC-6messageblockcheckbitse1,e2,e3,e4,e5,ande6arecontainedwithinmultiframebits194,966,1738,2510,3282and4054respectively,asshowninTable1/G.704.TheCRC-6messageblock（CMB）isasequenceof4632serialbitsthatiscoincidentwithamultiframe.Bydefinition,CMBNbeginsatbitposition1ofmultiframeNandendsatbitposition4632ofmultiframeN.ThefirsttransmittedCRCbitofamultiframeisthemostsignificantbitoftheCMBpolynomial.

IncalculatingtheCRC-6bits,theF-bitsarereplacedbybinary1s.Allinformationintheotherbitpositionswillbeidenticaltotheinformationinthecorrespondingmultiframebitpositions.

Thecheck-bitsequencee1throughe6transmittedinmultiframeN+1,istheremainderaftermultiplicationbyx6andthendivision（modulo2）bythegeneratorpolynomialx6+x+1ofthepolynomialcorrespondingtoCMBN.Thefirstcheckbit（e1）isthemostsignificantbitoftheremainder;thelastcheckbit（e6）istheleastsignificantbitoftheremainder.EachmultiframecontainstheCRC-6checkbitsgeneratedfortheprecedingCMB.

Atthereceiver,thereceivedCMB,witheachF-bithavingfirstbeenreplacedbyabinary1,isacteduponbythemultiplication/divisionprocessdescribedabove.Theresultingremainderiscomparedonabit-by-bitbasis,withtheCRC-6checkbitscontainedinthesubsequentlyreceivedmultiframe.Thecomparedcheckbitswillbeidenticalintheabsenceoftransmissionerrors.

2.1.3.1.34kbit/sdatalink

Beginningwithframe1ofthemultiframe（seeTable1/G.704）thefirstbitofeveryotherframeispartofthe4kbit/sdatalink.Thisdatalinkprovidesacommunicationpathbetweenprimaryhierarchicallevelterminalsandwillcontaindata,anidledatalinksequenceoralossofframealignmentalarmsequence.

Theformattobeusedforthetransmissionofdataoverthem-bitsofthedatalinkisstillunderstudy.

Theidledatalinkpatternisalsounderstudy.

Alossofframealignmentalarmsequenceisusedwhenalossofframealignment（LFA）conditionhasbeendetected.AfteralossofframealignmentconditionisdetectdatlocalendA,a16-bitLFAsequenceofeight1seight0s（1111111100000000）willbetransmittedinthem-bitsofthe4kbit/sdatalinkcontinuouslytoremoteendB.

2.1.3.2Method2:

Twelve-framemultiframe

AllocationoftheF-bittotheframealignmentsignal,multiframealignmentsignalandsignallingisgiveninTable2/G.704.

2.2Basicframestructureat6312kbit/s

2.2.1Framelength

Thenumberofbitsperframeis789.Theframerepetitionrateis8000Hz.

2.2.2F-bits

ThelastfivebitsofaframearedesignatedasF-bits,andareusedforsuchpurposesasframealignment,performancemonitoringandprovidingadatalink.

2.2.3AllocationofF-bits

AllocationoftheF-bitsisgiveninTable3/G.704.

TABLE3/G.704

AllocationofF-bits

Framenumber

Bitnumber

785

786

787

788

789

1

1

1

0

0

m

2

1

0

1

0

0

3

x

x

x

a

m

4

e1

e2

e3

e4

e5

mDatalinkbit.

aRemoteendalarmbit（1state=alarm,0state=noalarm）.

eiCRC-5checkbit（i=1to5）.

xSparebits,tobesetatstate1ifnotused.

2.2.3.1Framealignmentsignal

Theframeandmultiframealignmentsignalis110010100,andiscarriedontheF-bitsinframes1and2,excludingbit