ITU-T G.122 (03 1993) (英) Influence of national sy

INTERNATIONALTELECOMMUNICATIONUNION)454'TELECOMMUNICATION(03/93)STANDARDIZATIONSECTOROFITU42!.3-)33)/.3934%-3!.$-%$)!'%.%2!,#(!2!#4%2)34)#3/&.!4)/.!,3934%-3&/2-).'0!24/&).4%2.!4)/.!,#/..%#4)/.3).&,5%.#%/&.!4)/.!,3934%-3/.34!),)49!.$4!,+%2%#(/).).4%2.!4)/.!,#/..%#4)/.3)454Recommendation'(Previously“CCITTRecommendation”)FOREWORDTheITUTelecommunicationStandardizationSector(ITU-T)isapermanentorganoftheInternationalTelecom-municationUnion.TheITU-Tisresponsibleforstudyingtechnical,operatingandtariffquestionsandissuingRecommendationsonthemwithaviewtostandardizingtelecommunicationsonaworldwidebasis.TheWorldTelecommunicationStandardizationConference(WTSC),whichmeetseveryfouryears,establishedthetopicsforstudybytheITU-TStudyGroupswhich,intheirturn,produceRecommendationsonthesetopics.ITU-TRecommendationG.122wasrevisedbytheITU-TStudyGroupXII(1988-1993)andwasapprovedbytheWTSC(Helsinki,March1-12,1993).___________________NOTES1AsaconsequenceofareformprocesswithintheInternationalTelecommunicationUnion(ITU),theCCITTceasedtoexistasof28February1993.Initsplace,theITUTelecommunicationStandardizationSector(ITU-T)wascreatedasof1March1993.Similarly,inthisreformprocess,theCCIRandtheIFRBhavebeenreplacedbytheRadiocommunicationSector.InordernottodelaypublicationofthisRecommendation,nochangehasbeenmadeinthetexttoreferencescontainingtheacronyms“CCITT,CCIRorIFRB”ortheirassociatedentitiessuchasPlenaryAssembly,Secretariat,etc.FutureeditionsofthisRecommendationwillcontaintheproperterminologyrelatedtothenewITUstructure.2InthisRecommendation,theexpression“Administration”isusedforconcisenesstoindicatebothatelecommunicationadministrationandarecognizedoperatingagency.ITU1994Allrightsreserved.Nopartofthispublicationmaybereproducedorutilizedinanyformorbyanymeans,electronicormechanical,includingphotocopyingandmicrofilm,withoutpermissioninwritingfromtheITU.RecommendationG.122(03/93)iCONTENTSRecommendationG.122(03/93)Page1Introduction....................................................................................................................................................12Loss(a-b)toavoidinstabilityduringset-up,clear-downandchangesinaconnection................................23Unweightedloss(a-b)onestablishedconnections........................................................................................34Echoloss(a-b)onestablishedconnections....................................................................................................3AnnexA–Measurementofstabilityloss(a-b)andecholoss(a-b).........................................................................4AnnexB–Explanationoftermsassociatedwiththepatha-t-b...............................................................................6B.1Returnloss........................................................................................................................................6B.2Balancereturnloss............................................................................................................................6B.3Transmissionlossofthepatha-t-b...................................................................................................7B.4Stabilityandecholosses...................................................................................................................9B.5Overallloudnessratingoftheechopath(talkerecholoudnessrating,TELR)................................10B.6Summaryofusefulterms..................................................................................................................11References.................................................................................................................................................................11RecommendationG.122(03/93)1RecommendationG.122RecommendationG.122(03/93)INFLUENCEOFNATIONALSYSTEMSONSTABILITYANDTALKERECHOININTERNATIONALCONNECTIONS(Geneva,1964;amendedatMardelPlata,1968;Geneva,1972,1976and1980;Malaga-Torremolinos,1984;Melbourne,1988andHelsinki,1993)1IntroductionTheinformationprovidedinthisRecommendationappliestoallnationalsystems.RepresentationsofanationalsystemwhichextenduptothevirtualanalogueswitchingpointsareshowninFigure1.T1205550-93/d01BABAT3.5dBr–4dBr(foranalogueinternationalcircuit)–3.5dBr(fordigitalinternationalcircuit)Internationalcircuit.ATIONALSYSTEMPARTLYWIRE.ATIONALSYSTEMWHOLLYWIRENationalsystemNOTE–a,barethevirtualanalogueswitchingpointsoftheinternationalcircuit.FIGURE1/G.122NationalsystemrepresentationandvirtualanalogueswitchingpointdefinitionFIGURE1/G.122...[D01]=3CMThetransmissionlossintroducedbetweenaandbbythenationalsystem,referredtoastheloss(a-b),isimportantfromthreepointsofview:a)itcontributestothemarginthattheinternationalconnectionhasagainstoscillationduringthesetting-upandclearing-downoftheconnection.Aminimumlossovertheband0-4kHzisthecharacteristicvalue;b)itcontributestothemarginofstabilityduringacommunication.Again,aminimumlossintheband0-4kHzisthecharacteristicvalue,butinthiscasethesubs