1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS ISO/IEC TR 15294:2000
2、ICS 33.040.40; 35.200 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Information technology Methods for Data flow Control at Synchronous and Asynchronous DTE-DCE InterfacesThis British Standard, having been prepared under the direction of the DISC Committee, was published und
3、er the authority of the Standards Committee and comes into effect on 15 May 2000 BSI 05-2000 ISBN 0 580 34095 3 BS ISO/IEC TR 15294:2000 Amendments issued since publication Amd. No. Date Comments National foreword This British Standard reproduces verbatim ISO/IEC TR 15294:2000 and implements it as t
4、he UK national standard. The UK participation in its preparation was entrusted to Technical Committee IST/6, Data communications, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or
5、 proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement
6、international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to
7、 include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover,
8、the ISO/IEC TR title page, pages ii to iv, pages 1 to 6, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.Referencenumber ISO/IECTR15294:2000(E) TECHNICAL REPORT ISO/IEC TR 15294 Firstedition 2000-04-01 Information
9、technologyMethodsfordata flowcontrolatsynchronousand asynchronousDTE-DCEinterfaces Technologies de linformation Mthodes pour interfaces DTE-DCE synchrones et asynchrones de commande de flux de donnesISO/IECTR15294:2000(E) ii ISO/IECTR15294:2000(E)iii Foreword ISO(theInternationalOrganizationforStand
10、ardization)andIEC(theInternationalElectrotechnicalCommission) formthespecializedsystemforworldwidestandardization.NationalbodiesthataremembersofISOorIEC participateinthedevelopmentofInternationalStandardsthroughtechnicalcommitteesestablishedbythe respectiveorganizationtodealwithparticularfieldsoftec
11、hnicalactivity.ISOandIECtechnicalcommittees collaborateinfieldsofmutualinterest.Otherinternationalorganizations,governmentalandnon-governmental,in liaisonwithISOandIEC,alsotakepartinthework. InternationalStandardsaredraftedinaccordancewiththerulesgivenintheISO/IECDirectives,Part3. Inthefieldofinform
12、ationtechnology,ISOandIEChaveestablishedajointtechnicalcommittee,ISO/IECJTC1. DraftInternationalStandardsadoptedbythejointtechnicalcommitteearecirculatedtonationalbodiesforvoting. PublicationasanInternationalStandardrequiresapprovalbyatleast75%ofthenationalbodiescastingavote. Inexceptionalcircumstan
13、ces,whenatechnicalcommitteehascollecteddataofadifferentkindfromthatwhichis normallypublishedasanInternationalStandard(“stateoftheart“,forexample),itmaydecidebyasimplemajority voteofitsparticipatingmemberstopublishaTechnicalReport.ATechnicalReportisentirelyinformativeinnature anddoesnothavetobereview
14、eduntilthedataitprovidesareconsideredtobenolongervalidoruseful. AttentionisdrawntothepossibilitythatsomeoftheelementsofthisTechnicalReportmaybethesubjectofpatent rights.ISOandIECshallnotbeheldresponsibleforidentifyinganyorallsuchpatentrights. ISO/IECTR15294,waspreparedbyJointTechnicalCommitteeISO/IE
15、CJTC1, Information technology, SubcommitteeSC6, Telecommunications and information exchange between systems. ThisTechnicalReportistechnicallyalignedwithITU-TRecommendationV.43,butisnotpublishedasidentical text.ISO/IECTR15294:2000(E) iv Introduction WhenusingDCEsincorporatingdatacompressionand/orerro
16、rcorrection,itisessentialthattheDCEhavesome methodofcontrollingtheflowofdatafromtheDTE(asimilarrequirementappliesfortheassociatedDTEs,see below).Thisisbecausethedegreeofcompressionobtainedwillvaryfrommomenttomoment,andthebuffersin theDCEmayfillupduringperiodsoflowercompression,orwhilecorrectionoftra
17、nsmissionerrorsisactive. Likewise,duringperiodsofhighcompression,theDTEmaybecomeoverloadedwiththeamountofincomingdata andmaynotbeabletoprocessthisdataproperlywithoutmeansofcontrollingtheflowofdatafromtheDCE. Therearemanymethodsofflowcontrolinexistence,andDCEandDTEdesignersshouldensurethattheyprovide
18、 methodssuitablefortheassociatedDTEandDCE,respectively,tobeused. ThisRecommendationaimsatgivingguidelinesinordertoassistDTEandDCEdesignersintheirtasks.Itlists severalmechanismswhichareknowntooperatesuccessfullywithDTEsandDCEsalthoughnosinglemechanism willoperatewithallDTEsandDCEs,andsomeDTEsmaynotre
19、spondtoanyofthemechanismsdescribed.Both thesynchronousandtheasynchronousmodesofoperationareaddressed. NOTE TheguidelinesgiveninthisTechnicalReportmaynotbeexhaustive.TECHNICALREPORT ISO/IECTR15294:2000(E)1 InformationtechnologyMethodsfordataflowcontrolat synchronousandasynchronousDTE-DCEinterfaces 1
20、Scope ThisTechnicalReportprovidesguidanceforthechoiceofanappropriatemethodfor,andtheimplementationof, dataflowcontrolcapabilitiesinDTEsandDCEs.ItalsocoordinatesinformationfromotherRecommendationsand InternationalStandardsandprovidestutorialmaterialontheseflowcontroltechniques. 2 Reference 1ITU-TReco
21、mmendationV.24, List of definitions for interchange circuits between data terminal equipment and data circuit-terminating equipment. 3Abbreviation IRA Internationalreferencealphabet 4 DataFlowControlMethods Theguidanceisprovidedfor flowcontroloftransmitteddata, flowcontrolofreceiveddata. eachofwhich
22、issubdividedaccordingtoasynchronousandsynchronousmodesofoperation.Itisassumedthat theasynchronousmodeofoperationinthecontextofthisTechnicalReportisaccomplishedusingsynchronous DCEsincorporatingasynchronous-to-synchronousconversionaccordingtoe.g.RecommendationV.14orV.42. ThisTechnicalReportrestrictsi
23、tselftothedescriptionofmethodsforflowcontrolthatexistlocallybetweenaDTE andaDCE.Methodsforend-to-endflowcontrolinvolvingthetwoDTEsorthetwoDCEsconcernedarebeyond thescopeofthisTechnicalReport. AtpresentthisTechnicalReportdescribesonlyflowcontrolmethodsthatoperateatthephysicallayeroftheOSI ReferenceMo
24、del.InthecontextofthisTechnicalReport,theuseofDC1/DC3charactersisalsounderstoodasto fallinthiscategory.MethodsthatinvolvetheDCEimplementinglayer2orhigherlayerprotocols,forexample HDLC,areforfurtherstudy. 4.1 Methodsforflowcontroloftransmitteddata ThecontrolfunctionoftheDCEshallbecapableofindicatingt
25、otheDTEatemporaryinabilitytoacceptdataon circuit103,TransmittedData(DCEnot-readycondition).Uponreceivingsuchanindication,theDTEshallideally completetransmissionofanypartiallytransmittedcharacter(asynchronousmodeofoperation)orframe (synchronousmodeofoperation)andthenceasetransmittingdataoncircuit103a
26、ndclampcircuit103tobinary1. WhentheDCEnot-readyconditioniscleared,theDTEmayresumethetransmissionofdataoncircuit103.ISO/IECTR15294:2000(E) 2 Figure1depictstheinterchangecircuitsattheDTE-DCEinterfaceandthefunctionalitiesinsidetheDTEandthe DCE,respectively,whichmaybeused,asappropriate,fortheflowcontrol
27、oftransmitteddata. 103 106 112 114 104 A DC3/DC1 Flowcontrolof transmitteddata DC3/DC1 detection DTE DCE S/A A S Control function A DC3/DC1 Mux Datafrom higherlayer Output function Line Legend: A-applicablefortheasynchronousmodeofoperation S-applicableforthesynchronousmodeofoperation Line Figure1 4.
28、1.1 Asynchronousmodeofoperation Twostandardmethodsexist: 4.1.1.1 FlowcontrolbyuseofV.24interchangecircuits a) Useofcircuit106-Readyforsending TheDCEnot-readyconditionisindicatedbyturningcircuit106OFF,andclearedbyturningcircuit106ON. Thismethodshouldbethepreferredonebecauseitisunambiguousandisapplica
29、bletoanykindofdata communication.However,manyDTEswillnotimmediatelyrecognizetheOFFconditiononcircuit106andwillnot ceasetransmittingattheendofthepresentcharacter.Instead,theseDTEswillcompletethepresentframewhich maybeuptosomethousandoctetslong,andonlythendetecttheOFFconditiononcircuit106. Itistherefo
30、resuggestedthattheremainingbuffercapacityinsidetheDCEbekeptlargeenoughtocopewiththis condition.Areasonableremainingbuffersizesuggestedmaybebetween2,000and4,000octets,sothatthe minimumtotalbuffersizemaybebetween4,000octets(DCEnot-readyconditionisindicatedtotheDTEwhenthe bufferishalf-full)and10,000oct
31、ets(DCEnot-readyconditionisindicatedtotheDTEwhenabout80%ofthe bufferisfull). NOTE Thisassumesthataremainingbuffersizeofabout2,000octetsisneeded. ForaDTEtobeabletointerworkwithDCEsincorporatingdatacompressionand/orerrorcorrectionitisadvisable thattheDTEcyclicallychecktheconditionofcircuit106and,uponr
32、ecognitionoftheOFFconditiononcircuit106, stopthetransmissionofdataassoonaspossible.ISO/IECTR15294:2000(E)3 b) Useofcircuit112-Datasignallingrateselector(DCEsource) TheDCEmay,bycontrollingcircuit112,selectoneoftwodatasignallingratesintheDTEtocoincidewiththedata signallingrateinuseintheDCE. TheONcondi
33、tiononthiscircuitselectsthehigherrate,theOFFconditionselectsthelowerrate. 4.1.1.2 FlowcontrolbyuseofDC3/DC1characters TheDCEnot-readyconditionisindicatedbytransmittingaDC3character(IRAcharacter1/3),andclearedby transmittingaDC1character(IRAcharacter1/1),oncircuit104. Thismethodshouldnotbeappliedwhen
34、thereisariskthatbinarycharactersthatappearinthedatastreammay beconfusedwithDC3andDC1characters,whichwouldresultinamalfunctionofthesystem. SchemesthatindicateinbinaryfiletransferwhetheraDC3oraDC1characterthattheDTEdetectsinthedata transmittedoncircuit104eitherisgeneratedbytheDCEforthepurposeofflowcon
35、trol,orisabinarycharacter andpartofthedatareceivedfromtheremoteDTE,areforfurtherstudy. 4.1.2 Synchronousmodeofoperation Avarietyofmethodsisconceivableforthesynchronousmodeofoperation. 4.1.2.1 Flowcontrolbychangingtherateofthetransmittersignalelementtiming(DCEsource) Whenthetransmitclocksignalissourc
36、edfromtheDCE(circuit114),itmaybepossibletoslowthedataflowfrom theDTEbyreducingtheclockrate.TheclockrateshouldbehalvedbytheDCEand,ifthatactionisinsufficient, therateshouldbehalvedagain,andsoon.Theclockrateshouldbeincreasedagainassoonasconditionsinthe DCEhaveimproved. Thechangetoadifferentratehastoocc
37、urwhilecircuit114isintheOFFcondition. NOTE SomeDTEsusenarrow-bandphase-lockedloopsintheirreceivedclockcircuitryandmaynotbeabletorespondto thismechanism. 4.1.2.2 Flowcontrolbystoppingthetransmittersignalelementtimingsignal(DCEsource) Thismethodhaltstheclocksignaloncircuit114,thuscausingtheDTEtostopse
38、nding.Circuit114maybeheldin theOFFconditionforalimitedperiodoftime.ThedurationoftheOFFconditionshallbeanintegermultipleofthe lengthofasignalelementatthenormal(maximum)signallingrate.Signallingonthiscircuitmayberesumedata differentrate,asspecifiedabove. NOTE1 SomeDTEsmay-withorwithoutacertaintime-out
39、-raiseanalarmunderthiscondition. NOTE2 TherecommendedmaximumpermissibledurationofanOFFconditiononcircuit114isforfurtherstudy. 4.1.2.3 Flowcontrolbyuseofcircuit106 Circuit106(Readyforsending)maybeturnedOFFwhenthebuffersintheDCEarealmostfull(i.e.toaspecified degree).Thismethodofoperationfollowsthedefi
40、nitionofcircuit106inRecommendationV.24.Theconsiderations concerningtheDCEbuffersizegiveninsubclause4.1.1.1a)apply. IfthetransmitclockissourcedfromtheDTE(circuit113),thismaybetheonlyusablemethod.ISO/IECTR15294:2000(E) 4 4.2 Methodsforflowcontrolofreceiveddata TheDTEshallbecapableofindicatingtotheDCEa
41、temporaryinabilitytoacceptdataoncircuit104,Received Data(DTEnot-readycondition).Uponreceivingsuchanindication,theDCEshallcompletethedeliveryofany partiallytransmittedcharacter(asynchronousmodeofoperation)orframe(synchronousmodeofoperation)and thenceasedeliveringdatatotheDTEoncircuit104andclampcircui
42、t104tobinary1. WhentheDTEnot-readyconditioniscleared,theDCEmayresumethedeliveryofdataoncircuit104. NOTE ThedatawhoseflowistemporarilystoppedorsloweddownisoriginatedfromtheremoteDTE.Inordertocontrol theflowofthatdatasothatnodataislost,thelocalDCEwilleitherneedtoprovideareceiveddatabufferwhosesizecann
43、otbe specifiedinthisTechnicalReport,oramechanismwillneedtobeimplementedinthesystemtoforcetheremoteDTEtostop transmittingdatauntilsuchtimeastheDTEnot-readyconditioniscleared. Figure2depictstheinterchangecircuitsattheDTE-DCEinterfaceandthefunctionalitiesinsidetheDTEandthe DCE,respectively,whichmaybeus
44、ed,asappropriate,fortheflowcontrolofreceiveddata. Flowcontrolof receiveddata DTE DCE Legend: A-applicablefortheasynchronousmodeofoperation S-applicableforthesynchronousmodeofoperation 103 133 111 128 Control function DC3/DC1 detection Mux 104 Line Line Datato higher layer Output function A/S A/S S A
45、 DC3/DC1 A DC3/DC1 Figure2 4.2.1 Asynchronousmodeofoperation Thesametwostandardmethodsexistasforthecontroloftransmitteddata: 4.2.1.1 FlowcontrolbyuseofV.24interchangecircuits a) Useofcircuit133-Readyforreceiving TheDTEnot-readyconditionisindicatedbyturningOFFcircuit133,andisclearedbyturningcircuit13
46、3ON. Thismethodshouldbethepreferredoneasitisunambiguousandisapplicabletoanykindofdatacommunication. ItmaybeassumedthatmostDCEsrecognizewithonlyashortdelaythechangedconditiononcircuit133,andwill actaccordingly.TheremainingbuffersizeintheDTEmaythereforebekeptsmall.ISO/IECTR15294:2000(E)5 Thismethodisn
47、otapplicableforhalf-duplexprotocolsbecausecircuit105willnotbeavailableattheDCE.The DCEwillalwaysoperateintheconstantcarriermode. NOTE Inmanypublications,circuit133(Readyforreceiving)is,incorrectly,referredtoascircuit105(Requesttosend). Thesetwointerchangecircuitsaresignificantlydifferentintheirrespe
48、ctivedefinitionsandfunctions.Thesourceforconfusion maybethat,duetoalackoffreepolesontheinterfaceconnectorsstandardizedinISO/IEC2110andISO/IEC11569,both interchangecircuitsareallocatedtothesamepole(i.e.pole4)oftheseconnectors. b) Useofcircuit111-Datasignallingrateselector(DTEsource) TheDTEmayselecton
49、eoftwodatasignallingratesofadualratesynchronousDCEbyusingcircuit111.TheON conditionofthiscircuitselectsthehigherrate,theOFFconditionselectsthelowerrate. 4.2.1.2 FlowcontrolbyuseofDC3/DC1characters TheDTEnot-readyconditionisindicatedbytransmittingaDC3character(IRAcharacter1/3),andclearedby transmittingaDC1character(IRAcharacter1/1),oncircuit103,TransmittedData. Thismethodshouldnotbeappliedwhenthereisariskthatbinarycharactersthatappearinthedatastreammay beconfusedwithDC3andDC1characters,whichwouldresultinamalfunctionofthesystem. Schemesthatindicateinbinaryfiletransferwheth
