ITU-T G.322 (11 1988) (英) General characteristics

INTERNATIONALTELECOMMUNICATIONUNION)454'TELECOMMUNICATIONSTANDARDIZATIONSECTOROFITU).4%2.!4)/.!,!.!,/'5%#!22)%23934%-3).$)6)$5!,#(!2!#4%2)34)#3/&).4%2.!4)/.!,#!22)%24%,%0(/.%3934%-3/.-%4!,,)#,).%3'%.%2!,#(!2!#4%2)34)#32%#/--%.$%$&/23934%-3/.39--%42)#0!)2#!,%3)454Recommendation'(ExtractfromtheLUEOOK)NOTES1ITU-TRecommendationG.322waspublishedinFascicleIII.2oftheBlueBook.ThisfileisanextractfromtheBlueBook.WhilethepresentationandlayoutofthetextmightbeslightlydifferentfromtheBlueBookversion,thecontentsofthefileareidenticaltotheBlueBookversionandcopyrightconditionsremainunchanged(seebelow).2InthisRecommendation,theexpression“Administration”isusedforconcisenesstoindicatebothatelecommunicationadministrationandarecognizedoperatingagency.ITU1988,1993Allrightsreserved.Nopartofthispublicationmaybereproducedorutilizedinanyformorbyanymeans,electronicormechanical,includingphotocopyingandmicrofilm,withoutpermissioninwritingfromtheITU.FascicleIII.2-Rec.G.3221RecommendationG.322FascicleIII.2-Rec.G.322GENERALCHARACTERISTICSRECOMMENDEDFORSYSTEMSONSYMMETRICPAIRCABLESThisRecommendationappliestosystemsusingtypesofcablesofarrecommendedbytheCCITT(seeRecommendationG.611)andproviding1,2,3,4or5groupsor2supergroups.1Generalrecommendations1.1Hypotheticalreferencecircuits1.1.1Thehypotheticalreferencecircuitonsymmetricpairsis2500kmlong,andissetuponasymmetricpaircarriersystem.Foreachdirectionoftransmission,ithasatotalof:-threepairsofchannelmodulatorsanddemodulators,-sixpairsofgroupmodulatorsanddemodulators,-sixpairsofsupergroupmodulatorsanddemodulators1).Figure1/G.322showsadiagramofthehypotheticalreferencecircuitonsymmetricpairs.Itwillbeseenthatthereisatotalof15modulationsand15demodulationsforeachdirectionoftransmissionsupposingthateachmodulationordemodulationiseffectedbyasinglestage1).FIGURE1/G.322DiagramofthehypotheticalreferencecircuitonsymmetriccablepairsThishypotheticalreferencecircuitconsistsof6homogeneoussectionsofequallength(seeRecommendationG.212).Thenumberofpairsinthecableisassumedtobethesameinallsections.Thehypotheticalreferencecircuitonsymmetricpairsthusdefinedisusedforsystemsproviding1,2,3,4or5groups._______________1)Wheresystemsprovide1,2,3or4groups,itispossibletohaveasmallernumberofmodulations,butthisdoesnotdetractfromtheusefulnessoftheideaofahypotheticalreferencecircuitonsymmetricpairs.2FascicleIII.2-Rec.G.3221.1.2Thecompositionofthehypotheticalreferencecircuitfora10-group(2-supergroup)carriersystemshouldbethesameasthatofthehypotheticalreferencecircuitfora16-supergroupcoaxialcablesystem(see[1]).1.2DesignobjectivesforcircuitnoiseTheobjectivesmentionedinRecommendationG.222areapplicabletohypotheticalreferencecircuitsinthecircumstancesindicatedinRecommendationG.223.Inpractice,itissufficienttocheckbycalculationthat,foreverytelephonechannelasdefinedbythehypotheticalreferencecircuitonsymmetricpairs,themeanpsophometricpowerattheendofthechannelreferredtoapointofzerorelativeleveldoesnotexceed10000pW0pduringanyperiodofonehour.Thesubdivisionofthetotalnoisebetween:-basicnoise,-intermodulationnoise,-noiseduetocrosstalk,isleftentirelytothedesignerofthesystem,withinthelimitsof2500pW0pfortheterminalequipmentand7500pW0pfortheline.Note-Inplanningacarriersystemonsymmetricpairs,calculationofthenoiseduetocrosstalkcouldbecarriedoutbythemethodsdescribedin[2],[3]and[4].1.3Line-frequencyspectrum1.3.1Systemsproviding1,2or3groupsTheline-frequencyspectrumshouldbeinaccordancewiththeschemeshowninFigure2a)/G.322.1.3.2Systemsproviding4groupsThefrequencyspectrumtransmittedtolineshouldbeinaccordancewithScheme1ofFigure2b)/G.322.Note-ByagreementbetweentheAdministrationsconcerned,itispossibletoomitonegroupofsupergroup1*showninScheme2ofFigure2c)/G.322,forsystemswithfivegroups;ifthisisdone,Scheme1bisofFigure2b)/G.322,isobtained.1.3.3Systemsproviding5groupsThefrequencyspectrumtransmittedtolineshouldbeinaccordancewithScheme2ofFigure2c)/G.322.Note1-Wherethereisdirectinterconnectionbetweenasystemwith5groupsonsymmetricpairsandsystemswithasmallernumberofgroups,byagreementbetweentheAdministrationsconcerned,thesystemwith5groups,showninScheme2bisofFigure2c)/G.322,maybeused.Note2-ByagreementbetweentheAdministrationsconcerned,thearrangementinFigure3/G.322canbeusedforasupergrouponacoaxialcablesystemwhichistobeinterconnectedatbasicsupergroupfrequencies(312-552kHz)witheithera5-groupsystemonsymmetricpairsusingScheme2bis[Figure2c)/G.322],orwitha4-groupsystemusingScheme1[Figure2b)/G.322].SupplementNo.8[5]showsasimplewayofassemblingbasicgroupsBintoasupergroupinaccordancewithoneoftheschemesshowninFigure3/G.322andinFigure1/G.338[6]andviceversa.1.3.4Systemsproviding2supergroupsFascicleIII.2-Rec.G.3223ThefrequencyspectrumtransmittedtolineshouldbeinaccordancewitheitherScheme3orScheme4ofFigure4/G.322,whichevertheAdministrationdecides.Supergroups1and2arethesameasthoseincoaxialcablecarriersystems.Supergroup1*isthesameasthatnormallyrecommendedfor5-groupsystemsonsymmetriccablepairs.4FascicleIII.2-Rec.G.322Note-ByagreementbetweentheAdministrations