翻译文献-逻辑链路控制和适配协议详述

外文原文LOGICALLINKCONTROLANDADAPTATIONPROTOCOLSPECIFICATION1INTRODUCTIONTHISSECTIONOFTHEBLUETOOTHSPECIFICATIONDEFINESTHELOGICALLINKCONTROLANDADAPTATIONLAYERPROTOCOL,REFERREDTOASL2CAPL2CAPISLAYEREDOVERTHELINKCONTROLLERPROTOCOLANDRESIDESINTHEDATALINKLAYERASSHOWNINFIGURE11L2CAPPROVIDESCONNECTIONORIENTEDANDCONNECTIONLESSDATASERVICESTOUPPERLAYERPROTOCOLSWITHPROTOCOLMULTIPLEXINGCAPABILITY,SEGMENTATIONANDREASSEMBLYOPERATION,ANDGROUPABSTRACTIONSL2CAPPERMITSHIGHERLEVELPROTOCOLSANDAPPLICATIONSTOTRANSMITANDRECEIVEUPPERLAYERDATAPACKETSL2CAPSERVICEDATAUNITS,SDUUPTO64KILOBYTESINLENGTHL2CAPALSOPERMITSPERCHANNELFLOWCONTROLANDRETRANSMISSIONVIATHEFLOWCONTROLANDRETRANSMISSIONMODESFIGURE11L2CAPWITHINPROTOCOLLAYERSTHEL2CAPLAYERPROVIDESLOGICALCHANNELS,NAMEDL2CAPCHANNELS,WHICHAREMAPPEDTOL2CAPLOGICALLINKSSUPPORTEDBYANACLLOGICALTRANSPORT,SEEBASEBANDSPECIFICATIONVOL2,PARTBSECTION44ONPAGE8611L2CAPFEATURESTHEFUNCTIONALREQUIREMENTSFORL2CAPINCLUDEPROTOCOL/CHANNELMULTIPLEXING,SEGMENTATIONANDREASSEMBLYSAR,PERCHANNELFLOWCONTROL,ERRORCONTROLANDGROUPMANAGEMENTFIGURE12ONPAGE22ILLUSTRATESHOWL2CAPDATAFLOWSFITINTOTHEBLUETOOTHPROTOCOLSTACKL2CAPLIESABOVETHELINKCONTROLLERPROTOCOLANDINTERFACESWITHOTHERCOMMUNICATIONPROTOCOLSSUCHASTHEBLUETOOTHSERVICEDISCOVERYPROTOCOLSDP,RFCOMM,TELEPHONYCONTROLTCSANDBLUETOOTHNETWORKENCAPSULATIONPROTOCOLBNEPVOICEQUALITYCHANNELSFORAUDIOANDTELEPHONYAPPLICATIONSANDSYNCHRONOUSTRANSPARENTCONNECTIONSAREUSUALLYRUNOVERSYNCHRONOUSLOGICALTRANSPORTS,SEEVOL2,PARTBSECTION43ONPAGE86PACKETIZEDAUDIODATA,SUCHASIPTELEPHONY,MAYBESENTUSINGCOMMUNICATIONPROTOCOLSRUNNINGOVERL2CAPTHEL2CAPLAYERPROVIDESLOGICALCHANNELS,NAMEDL2CAPCHANNELS,WHICHAREMAPPEDTOL2CAPLOGICALLINKSSUPPORTEDBYANACLLOGICALTRANSPORT,SEEBASEBANDSPECIFICATIONVOL2,PARTBSECTION44ONPAGE8611L2CAPFEATURESTHEFUNCTIONALREQUIREMENTSFORL2CAPINCLUDEPROTOCOL/CHANNELMULTIPLEXING,SEGMENTATIONANDREASSEMBLYSAR,PERCHANNELFLOWCONTROL,ERRORCONTROLANDGROUPMANAGEMENTFIGURE12ONPAGE22ILLUSTRATESHOWL2CAPDATAFLOWSFITINTOTHEBLUETOOTHPROTOCOLSTACKL2CAPLIESABOVETHELINKCONTROLLERPROTOCOLANDINTERFACESWITHOTHERCOMMUNICATIONPROTOCOLSSUCHASTHEBLUETOOTHSERVICEDISCOVERYPROTOCOLSDP,RFCOMM,TELEPHONYCONTROLTCSANDBLUETOOTHNETWORKENCAPSULATIONPROTOCOLBNEPVOICEQUALITYCHANNELSFORAUDIOANDTELEPHONYAPPLICATIONSANDSYNCHRONOUSTRANSPARENTCONNECTIONSAREUSUALLYRUNOVERSYNCHRONOUSLOGICALTRANSPORTS,PACKETIZEDAUDIODATA,SUCHASIPTELEPHONY,MAYBESENTUSINGCOMMUNICATIONPROTOCOLSRUNNINGOVERL2CAPFIGURE13BREAKSDOWNL2CAPINTOITSARCHITECTURALCOMPONENTSTHECHANNELMANAGERPROVIDESTHECONTROLPLANEFUNCTIONALITYANDISRESPONSIBLEFORALLINTERNALSIGNALLING,L2CAPPEERTOPEERSIGNALLINGANDSIGNALLINGWITHHIGHERANDLOWERLAYERSITPERFORMSTHESTATEMACHINEFUNCTIONALITYDESCRIBEDINSECTION6ANDUSESMESSAGEFORMATSDESCRIBEDINSECTION4ONTHERETRANSMISSIONANDFLOWCONTROLBLOCKPROVIDESPERCHANNELFLOWCONTROLANDOPTIONALRETRANSMISSIONFORAPPLICATIONSTHATREQUIREITTHERESOURCEMANAGERISRESPONSIBLEFORPROVIDINGAFRAMERELAYSERVICETOTHECHANNELMANAGER,THERETRANSMISSIONANDFLOWCONTROLBLOCKANDTHOSEAPPLICATIONDATASTREAMSTHATDONOTREQUIRERETRANSMISSIONANDFLOWCONTROLSERVICESITISRESPONSIBLEFORCOORDINATINGTHETRANSMISSIONANDRECEPTIONOFPACKETSRELATEDTOMULTIPLEL2CAPCHANNELSOVERTHEFACILITIESOFFEREDATTHELOWERLAYERINTERFACEPROTOCOL/CHANNELMULTIPLEXINGL2CAPSUPPORTSMULTIPLEXINGBECAUSETHEBASEBANDPROTOCOLDOESNOTSUPPORTANYTYPEFIELDIDENTIFYINGTHEHIGHERLAYERPROTOCOLBEINGMULTIPLEXEDABOVEITDURINGCHANNELSETUP,PROTOCOLMULTIPLEXINGCAPABILITYISUSEDTOROUTETHECONNECTIONREQUESTTOTHECORRECTUPPERLAYERPROTOCOLFORDATATRANSFER,LOGICALCHANNELMULTIPLEXINGISNEEDEDTODISTINGUISHBETWEENMULTIPLEUPPERLAYERENTITIESTHEREMAYBEMORETHANONEUPPERLAYERENTITYUSINGTHESAMEPROTOCOLSEGMENTATIONANDREASSEMBLYWITHTHEFRAMERELAYSERVICEOFFEREDBYTHERESOURCEMANAGER,THELENGTHOFTRANSPORTFRAMESISCONTROLLEDBYTHEINDIVIDUALAPPLICATIONSRUNNINGOVERL2CAPMANYMULTIPLEXEDAPPLICATIONSAREBETTERSERVEDIFL2CAPHASCONTROLOVERTHEPDULENGTHTHISPROVIDESTHEFOLLOWINGBENEFITSASEGMENTATIONWILLALLOWTHEINTERLEAVINGOFAPPLICATIONDATAUNITSINORDERTOSATISFYLATENCYREQUIREMENTSBMEMORYANDBUFFERMANAGEMENTISEASIERWHENL2CAPCONTROLSTHEPACKETSIZECERRORCORRECTIONBYRETRANSMISSIONCANBEMADEMOREEFFICIENTDTHEAMOUNTOFDATATHATISDESTROYEDWHENANL2CAPPDUISCORRUPTEDORLOSTCANBEMADESMALLERTHANTHEAPPLICATIONSDATAUNITETHEAPPLICATIONISDECOUPLEDFROMTHESEGMENTATIONREQUIREDTOMAPTHEAPPLICATIONPACKETSINTOTHELOWERLAYERPACKETSFLOWCONTROLPERL2CAPCHANNELWHENSEVERALDATASTREAMSRUNOVERTHESAMEL2CAPLOGICALLINK,USINGSEPARATEL2CAPCHANNELS,EACHCHANNELMAYREQUIREINDIVIDUALFLOWCONTROLALSOL2CAPPROVIDESFLOWCONTROLSERVICESTOPROFILESORAPPLICATIONSTHATNEEDFLOWCONTROLANDCANAVOIDHAVINGTOIMPLEMENTITDUETOTHEDELAYSBETWEENTHEL2CAPLAYERS,STOPANDGOFLOWCONTROLASEMPLOYEDINTHEBASEBANDISNOTSUFFICIENTAWINDOWBASEDFLOWCONTROLSCHEMEISPROVIDEDTHEUSEOFFLOWCONTROLISANOPTIONALASPECTOFTHEL2CAPPROTOCOLERRORCONTROLANDRETRANSMISSIONSSOMEAPPLICATIONSREQUIREARESIDUALERRORRATEMUCHSMALLERTHANTHEBASEBANDCANDELIVERL2CAPINCLUDESOPTIONALERRORCHECKSANDRETRANSMISSIONSOFL2CAPPDUSTHEERRORCHECKINGINL2CAPPROTECTSAGAINSTERRORSDUETOTHEBASEBANDFALSELYACCEPTINGPACKETHEADERSANDDUETOFAILURESOFTHEHECORCRCERRORCHECKSONTHEBASEBANDPACKETSRETRANSMISSIONMODEALSOPROTECTSAGAINSTLOSSOFPACKETSDUETOFLUSHONTHESAMELOGICALTRANSPORTTHEERRORCONTROLWORKSINCONJUNCTIONWITHFLOWCONTROLINTHESENSETHATTHEFLOWCONTROLMECHANISMWILLTHROTTLERETRANSMISSIONSASWELLASFIRSTTRANSMISSIONSTHEUSEOFERRORCONTROLANDRETRANSMISSIONPROCEDURESISOPTIONALFRAGMENTATIONANDRECOMBINATIONTHELOWERLAYERSHAVELIMITEDTRANSMISSIONCAPABILITIESANDMAYREQUIREFRAGMENTSIZESDIFFERENTFROMTHOSECREATEDBYL2CAPSEGMENTATIONTHEREFORELAYERSBELOWL2CAPMAYFURTHERFRAGMENTANDRECOMBINEL2CAPPDUSTOCREATEFRAGMENTSWHICHFITEACHLAYERCAPABILITIESDURINGTRANSMISSIONOFANL2CAPPDU,MANYDIFFERENTLEVELSOFFRAGMENTATIONANDRECOMBINATIONMAYOCCURINBOTHPEERDEVICESTHEHCIDRIVERORCONTROLLERMAYFRAGMENTL2CAPPDUSTOHONORPACKETSIZECONSTRAINTSOFAHOSTCONTROLLERINTERFACETRANSPORTSCHEMETHISRESULTSINHCIDATAPACKETPAYLOADSCARRYINGSTARTANDCONTINUATIONFRAGMENTSOFTHEL2CAPPDUSIMILARLYTHELINKCONTROLLERMAYFRAGMENTL2CAPPDUSTOMAPTHEMINTOBASEBANDPACKETSTHISRESULTSINBASEBANDPACKETPAYLOADSCARRYINGSTARTANDCONTINUATIONFRAGMENTSOFTHEL2CAPPDUEACHLAYEROFTHEPROTOCOLSTACKMAYPASSONDIFFFERENTSIZEDFRAGMENTSOFL2CAPPDUS,ANDTHESIZEOFFRAGMENTSCREATEDBYALAYERMAYBEDIFFERENTINEACHPEERDEVICEHOWEVERTHEPDUISFRAGMENTEDWITHINTHESTACK,THERECEIVINGL2CAPENTITYSTILLRECOMBINESTHEFRAGMENTSTOOBTAINTHEORIGINALL2CAPPDUQUALITYOFSERVICETHEL2CAPCONNECTIONESTABLISHMENTPROCESSALLOWSTHEEXCHANGEOFINFORMATIONREGARDINGTHEQUALITYOFSERVICEQOSEXPECTEDBETWEENTWOBLUETOOTHDEVICESEACHL2CAPIMPLEMENTATIONMONITORSTHERESOURCESUSEDBYTHEPROTOCOLANDENSURESTHATQOSCONTRACTSAREHONORED12ASSUMPTIONSTHEPROTOCOLISDESIGNEDBASEDONTHEFOLLOWINGASSUMPTIONS1THEACLLOGICALTRANSPORTANDL2CAPLOGICALLINKBETWEENTWODEVICESISSETUPUSINGTHELINKMANAGERPROTOCOLTHEBASEBANDPROVIDESORDERLYDELIVERYOFDATAPACKETS,ALTHOUGHTHEREMIGHTBEINDIVIDUALPACKETCORRUPTIONANDDUPLICATESNOMORETHAN1UNICASTACLLOGICALTRANSPORTEXISTSBETWEENANYTWODEVICES2THEBASEBANDALWAYSPROVIDESTHEIMPRESSIONOFFULLDUPLEXCOMMUNICATIONCHANNELSTHISDOESNOTIMPLYTHATALLL2CAPCOMMUNICATIONSAREBIDIRECTIONALMULTICASTSANDUNIDIRECTIONALTRAFFICEG,VIDEODONOTREQUIREDUPLEXCHANNELS3THEL2CAPLAYERPROVIDESACHANNELWITHADEGREEOFRELIABILITYBASEDONTHEMECHANISMSAVAILABLEATTHEBASEBANDLAYERANDWITHOPTIONALADDITIONALPACKETSEGMENTATIONANDERRORDETECTIONTHATCANBEENABLEDINTHEENHANCEDL2CAPLAYERTHEBASEBANDPERFORMSDATAINTEGRITYCHECKSANDRESENDSDATAUNTILITHASBEENSUCCESSFULLYACKNOWLEDGEDORATIMEOUTOCCURSBECAUSEACKNOWLEDGEMENTSMAYBELOST,TIMEOUTSMAYOCCUREVENAFTERTHEDATAHASBEENSUCCESSFULLYSENTTHELINKCONTROLLERPROTOCOLUSESA1BITSEQUENCENUMBERNOTETHATTHEUSEOFBASEBANDBROADCASTPACKETSISPROHIBITEDIFRELIABILITYISREQUIRED,SINCEALLBROADCASTSSTARTTHEFIRSTSEGMENTOFANL2CAPPACKETWITHTHESAMESEQUENCEBIT4SOMEAPPLICATIONSWILLEXPECTINDEPENDENTFLOWCONTROL,INDEPENDENCEFROMTHEEFFECTSOFOTHERTRAFFICAND,INSOMECASES,BETTERERRORCONTROLTHANTHEBASEBANDPROVIDESTHEFLOWANDERRORCONTROLBLOCKPROVIDESTWOMODESRETRANSMISSIONMODEOFFERSSEGMENTATION,FLOWCONTROLANDL2CAPPDURETRANSMISSIONSFLOWCONTROLMODEOFFERSJUSTTHESEGMENTATIONANDFLOWCONTROLFUNCTIONSIFBASICL2CAPMODEISCHOSEN,THEFLOWANDERRORCONTROLBLOCKISNOTUSED13SCOPETHEFOLLOWINGFEATURESAREOUTSIDETHESCOPEOFL2CAPSRESPONSIBILITIESL2CAPDOESNOTTRANSPORTAUDIOORTRANSPARENTSYNCHRONOUSDATADESIGNATEDFORSCOORESCOLOGICALTRANSPORTSL2CAPDOESNOTSUPPORTARELIABLEMULTICASTCHANNELSEESECTION32ONPAGE34L2CAPDOESNOTSUPPORTTHECONCEPTOFAGLOBALGROUPNAME2GENERALOPERATIONL2CAPISBASEDAROUNDTHECONCEPTOFCHANNELSEACHONEOFTHEENDPOINTSOFANL2CAPCHANNELISREFERREDTOBYACHANNELIDENTIFIERCID21CHANNELIDENTIFIERSACHANNELIDENTIFIERCIDISTHELOCALNAMEREPRESENTINGALOGICALCHANNELENDPOINTONTHEDEVICETHENULLIDENTIFIER0X0000ISANILLEGALIDENTIFIERANDSHALLNEVERBEUSEDASADESTINATIONENDPOINTIDENTIFIERSFROM0X0001TO0X003FARERESERVEDFORSPECIFICL2CAPFUNCTIONSIMPLEMENTATIONSAREFREETOMANAGETHEREMAININGCIDSINAMANNERBESTSUITEDFORTHATPARTICULARIMPLEMENTATION,WITHTHEPROVISIONTHATTWOSIMULTANEOUSLYACTIVEL2CAPCHANNELSSHALLNOTSHARETHESAMECIDSUMMARIZESTHEDEFINITIONANDPARTITIONINGOFTHECIDNAMESPACECIDASSIGNMENTISRELATIVETOAPARTICULARDEVICEANDADEVICECANASSIGNCIDSINDEPENDENTLYFROMOTHERDEVICESUNLESSITNEEDSTOUSEANYOFTHERESERVEDCIDSSHOWNINTHETABLEBELOWTHUS,EVENIFTHESAMECIDVALUEHASBEENASSIGNEDTOREMOTECHANNELENDPOINTSBYSEVERALREMOTEDEVICESCONNECTEDTOASINGLELOCALDEVICE,THELOCALDEVICECANSTILLUNIQUELYASSOCIATEEACHREMOTECIDWITHADIFFERENTDEVICE22OPERATIONBETWEENDEVICESFIGURE21ONPAGE30ILLUSTRATESTHEUSEOFCIDSINACOMMUNICATIONBETWEENCORRESPONDINGPEERL2CAPENTITIESINSEPARATEDEVICESTHECONNECTIONORIENTEDDATACHANNELSREPRESENTACONNECTIONBETWEENTWODEVICES,WHEREACIDIDENTIFIESEACHENDPOINTOFTHECHANNELTHECONNECTIONLESSCHANNELSRESTRICTDATAFLOWTOASINGLEDIRECTIONTHESECHANNELSAREUSEDTOSUPPORTACHANNELGROUPWHERETHECIDONTHESOURCEREPRESENTSONEORMOREREMOTEDEVICESTHEREAREALSOANUMBEROFCIDSRESERVEDFORSPECIALPURPOSESTHESIGNALLINGCHANNELISONEEXAMPLEOFARESERVEDCHANNELTHISCHANNELISUSEDTOCREATEANDESTABLISHCONNECTIONORIENTEDDATACHANNELSANDTONEGOTIATECHANGESINTHECHARACTERISTICSOFCONNECTIONORIENTEDANDCONNECTIONLESSCHANNELSSUPPORTFORASIGNALLINGCHANNELWITHINANL2CAPENTITYISMANDATORYNOTEITISASSUMEDTHATANL2CAPSIGNALLINGCHANNELISAVAILABLEIMMEDIATELYWHENANACLLOGICALTRANSPORTISESTABLISHEDBETWEENTWODEVICES,ANDL2CAPTRAFFICISENABLEDONTHEL2CAPLOGICALLINKANOTHERCIDISRESERVEDFORALLINCOMINGCONNECTIONLESSDATATRAFFICINTHEEXAMPLEBELOW,ACIDISUSEDTOREPRESENTAGROUPCONSISTINGOFDEVICE3AND4TRAFFICSENTFROMTHISCHANNELIDISDIRECTEDTOTHEREMOTECHANNELRESERVEDFORCONNECTIONLESSDATATRAFFIC23OPERATIONBETWEENLAYERSL2CAPIMPLEMENTATIONSSHOULDFOLLOWTHEGENERALARCHITECTUREDESCRIBEDBELOWL2CAPIMPLEMENTATIONSTRANSFERDATABETWEENUPPERLAYERPROTOCOLSANDTHELOWERLAYERPROTOCOLTHISDOCUMENTLISTSANUMBEROFSERVICESTHATSHOULDBEEXPORTEDBYANYL2CAPIMPLEMENTATIONEACHIMPLEMENTATIONSHALLALSOSUPPORTASETOFSIGNALLINGCOMMANDSFORUSEBETWEENL2CAPIMPLEMENTATIONSL2CAPIMPLEMENTATIONSSHOULDALSOBEPREPAREDTOACCEPTCERTAINTYPESOFEVENTSFROMLOWERLAYERSANDGENERATEEVENTSTOUPPERLAYERSHOWTHESEEVENTSAREPASSEDBETWEENLAYERSISIMPLEMENTATIONSPECIFIC24MODESOFOPERATIONL2CAPMAYOPERATEINONEOFTHREEDIFFERENTMODESASSELECTEDFOREACHL2CAPCHANNELBYANUPPERLAYERTHEMODESAREBASICL2CAPMODEEQUIVALENTTOL2CAPSPECIFICATIONINBLUETOOTHV111FLOWCONTROLMODERETRANSMISSIONMODETHEMODESAREENABLEDUSINGTHECONFIGURATIONPROCEDURETHEBASICL2CAPMODEISTHEDEFAULTMODE,WHICHISUSEDWHENNOOTHERMODEISAGREEDINFLOWCONTROLANDRETRANSMISSIONMODES,PDUSEXCHANGEDWITHAPEERENTITYARENUMBEREDANDACKNOWLEDGEDTHESEQUENCENUMBERSINTHEPDUSAREUSEDTOCONTROLBUFFERING,ANDATXWINDOWSIZEISUSEDTOLIMITTHEREQUIREDBUFFERSPACEAND/ORPROVIDEAMETHODFORFLOWCONTROLINADDITIONTOTHEWINDOWSIZE,THETOKENBUCKETSIZEPARAMETEROFTHEFLOWSPECIFICATIONCANBEUSEDTODIMENSIONTHEBUFFERSINPARTICULARONCHANNELSTHATDONOTUSEFLOWANDERRORCONTROLINFLOWCONTROLMODENORETRANSMISSIONSTAKEPLACE,BUTMISSINGPDUSAREDETECTEDANDCANBEREPORTEDASLOSTINRETRANSMISSIONMODEATIMERISUSEDTOENSURETHATALLPDUSAREDELIVEREDTOTHEPEER,BYRETRANSMITINGPDUSASNEEDEDAGOBACKNREPEATMECHANISMISUSEDTOSIMPLIFYTHEPROTOCOLANDLIMITTHEBUFFERINGREQUIREMENTS3DATAPACKETFORMATL2CAPISPACKETBASEDBUTFOLLOWSACOMMUNICATIONMODELBASEDONCHANNELSACHANNELREPRESENTSADATAFLOWBETWEENL2CAPENTITIESINREMOTEDEVICESCHANNELSMAYBECONNECTIONORIENTEDORCONNECTIONLESSALLPACKETFIELDSSHALLUSELITTLEENDIANBYTEORDER31CONNECTIONORIENTEDCHANNELINBASICL2CAPMODEFIGURE31ONPAGE33ILLUSTRATESTHEFORMATOFTHEL2CAPPDUWITHINACONNECTIONORIENTEDCHANNELINBASICL2CAPMODE,THEL2CAPPDUONACONNECTIONORIENTEDCHANNELISALSOREFERREDTOASA“BFRAME“THEFIELDSSHOWNARELENGTH2OCTETS16BITSLENGTHINDICATESTHESIZEOFTHEINFORMATIONPAYLOADINOCTETS,EXCLUDINGTHELENGTHOFTHEL2CAPHEADERTHELENGTHOFANINFORMATIONPAYLOADCANBEUPTO65535OCTETSTHELENGTHFIELDISUSEDFORRECOMBINATIONANDSERVESASASIMPLEINTEGRITYCHECKOFTHERECOMBINEDL2CAPPACKETONTHERECEIVINGENDCHANNELID2OCTETSTHECHANNELIDCIDIDENTIFIESTHEDESTINATIONCHANNELENDPOINTOFTHEPACKETINFORMATIONPAYLOAD0TO65535OCTETSTHISCONTAINSTHEPAYLOADRECEIVEDFROMTHEUPPERLAYERPROTOCOLOUTGOINGPACKET,ORDELIVEREDTOTHEUPPERLAYERPROTOCOLINCOMINGPACKETTHEMTUISDETERMINEDDURINGCHANNELCONFIGURATIONSEESECTION51ONPAGE57THEMINIMUMSUPPORTEDMTUFORTHESIGNALLINGPDUSMTUSIGIS48OCTETSSEESECTION4ONPAGE414SIGNALLINGPACKETFORMATSTHISSECTIONDESCRIBESTHESIGNALLINGCOMMANDSPASSEDBETWEENTWOL2CAPENTITIESONPEERDEVICESALLSIGNALLINGCOMMANDSARESENTTOTHESIGNALLINGCHANNELWITHCID0X0001THISSIGNALLINGCHANNELISAVAILABLEASSOONASANACLLOGICALTRANSPORTISSETUPANDL2CAPTRAFFICISENABLEDONTHEL2CAPLOGICALLINKFIGURE41ONPAGE41ILLUSTRATESTHEGENERALFORMATOFL2CAPPDUSCONTAININGSIGNALLINGCOMMANDSCFRAMESMULTIPLECOMMANDSMAYBESENTINASINGLECFRAMECOMMANDSTAKETHEFORMOFREQUESTSANDRESPONSESALLL2CAPIMPLEMENTATIONSSHALLSUPPORTTHERECEPTIONOFCFRAMESWITHAPAYLOADLENGTHTHATDOESNOTEXCEEDTHESIGNALINGMTUTHEMINIMUMSUPPORTEDPAYLOADLENGTHFORTHECFRAMEMTUSIGIS48OCTETSL2CAPIMPLEMENTATIONSSHOULDNOTUSECFRAMESTHATEXCEEDTHEMTUSIGOFTHEPEERDEVICEIFTHEYEVERDO,THEPEERDEVICESHALLSENDACOMMANDREJECTCONTAININGTHESUPPORTEDMTUSIGIMPLEMENTATIONSMUSTBEABLETOHANDLETHERECEPTIONOFMULTIPLECOMMANDSINANL2CAPPACKET5CONFIGURATIONPARAMETEROPTIONSOPTIONSAREAMECHANISMTOEXTENDTHECONFIGURATIONPARAMETERSOPTIONSSHALLBETRANSMITTEDASINFORMATIONELEMENTSCONTAININGANOPTIONTYPE,ANOPTIONLENGTH,ANDONEORMOREOPTIONDATAFIELDSFIGURE51ILLUSTRATESTHEFORMATOFANOPTIONTHECONFIGURATIONOPTIONFIELDSARETYPE1OCTETTHEOPTIONTYPEFIELDDEFINESTHEPARAMETERSBEINGCONFIGUREDTHEMOSTSIGNIFICANTBITOFTHETYPEDETERMINESTHEACTIONTAKENIFTHEOPTIONISNOTRECOGNIZED0OPTIONMUSTBERECOGNIZEDIFTHEOPTIONISNOTRECOGNIZEDTHENREFUSETHECONFIGURATIONREQUEST1OPTIONISAHINTIFTHEOPTIONISNOTRECOGNIZEDTHENSKIPTHEOPTIONANDCONTINUEPROCESSINGLENGTH1OCTETTHELENGTHFIELDDEFINESTHENUMBEROFOCTETSINTHEOPTIONDATATHUSANOPTIONTYPEWITHOUTOPTIONDATAHASALENGTHOF0OPTIONDATATHECONTENTSOFTHISFIELDAREDEPENDENTONTHEOPTIONTYPE6GENERALPROCEDURESTHISSECTIONDESCRIBESTHEGENERALOPERATIONOFL2CAP,INCLUDINGTHECONFIGURATIONPROCESS,THEHANDLINGANDTHEPROCESSINGOFUSERDATAFORTRANSPORTATIONOVERTHEAIRINTERFACETHISSECTIONALSODESCRIBESTHEOPERATIONOFL2CAPFEATURESCONFIGURINGTHECHANNELPARAMETERSSHALLBEDONEINDEPENDENTLYFORBOTHDIRECTIONSBOTHCONFIGURATIONSMAYBEDONEINPARALLELFOREACHDIRECTIONTHEFOLLOWINGPROCEDURESHALLBEUSED1INFORMINGTHEREMOTESIDEOFTHENONDEFAULTPARAMETERSTHATTHELOCALSIDEWILLACCEPTUSINGACONFIGURATIONREQUEST2REMOTESIDERESPONDS,AGREEINGORDISAGREEINGWITHTHESEVALUES,INCLUDINGTHEDEFAULTONES,USINGACONFIGURATIONRESPONSE3THELOCALANDREMOTEDEVICESREPEATSTEPS1AND2UNTILAGREEMENTONALLPARAMETERSISREACHEDTHISPROCESSCANBEABSTRACTEDINTOTHEINITIALREQUESTCONFIGURATIONPATHANDARESPONSECONFIGURATIONPATH,FOLLOWEDBYTHEREVERSEDIRECTIONPHASERECONFIGURATIONFOLLOWSASIMILARTWOPHASEPROCESSBYREQUIRINGCONFIGURATIONINBOTHDIRECTIONSTHEDECISIONONTHEAMOUNTOFTIMEORMESSAGESSPENTCONFIGURINGTHECHANNELPARAMETERSBEFORETERMINATINGTHECONFIGURATIONISLEFTTOTHEIMPLEMENTATION,BUTITSHALLNOTLASTMORETHAN120SECONDS逻辑链路控制和适配协议详述1绪论蓝牙领域的这部分把逻辑链路控制和适配协议定义成提到的L2CAP，L2CAP由连接控制协议所覆盖并置于数据链接层，L2CAP允许高层协议和应用程序收发最长64K的数据包。正如图11L2CAP所显示的那样，它提供链接向导并凭借协议多路技术功能分割和集合操作以及成批提取，向更高层协议提供更高层无链接服务。L2CAP也允许管道流控制和中继通过控制流和中继模式。11L2CAP的特点L2CAP的功能需求包括协议/管道多路技术,分割和合成,每条管道流控制和群体管理，如图12显示L2CAP数据如何适配蓝牙协议栈，L2CAP位于连接控制协议和其它交流协议例如SDP,TCS和NEP相连接音质管道提供音频和电话应用软件和同步明晰的链接关系通常超出同时传输的限度。L2CAP提供管理的管道称为L2CAP管道它为ACL逻辑所传输支持的逻辑链路同步L2CAP。外文原文11逻辑链路控制和适配协议的特征。L2CAP主要为上层提供如下服务1协议复用多个高层协议共享一个公共的物理连接，从逻辑上看每个协议都有自己的独立数据通道，但由于基带协议不能识别其他高层协议，所以L2CAP必须支持上层协议复用，它能区分诸如服务发现协议（SDP），RFCOMM，电话控制协议（TCS）等高层协议，这点与TCP/IP协议族中IP的协议复用功能是相似的。2分段与重组与有线的物理媒质相比，蓝牙基带协议的数据包的大小是非常有限的。最大的基带包只能传输341个字节的信息，这就限制了高层协议带宽的有效使用。这样，大的L2CAP包必须分解成小的基带包来发送。同样的，在接收方，必需将多个基带包重组为一个完整的L2CAP数据包。3服务质量在L2CAP建立连接的过程中允许改变两台蓝牙设备间的服务质量。每个L2CAP实体必须监视协议使用的资源并保证服务质量（QOS）的实现。4组的概念很多协议支持组地址的概念，蓝牙的基带协议支持微微网，即一组设备使用同一时钟同步跳频，L2CAP的组提取功能可以有效地将协议的组映射为基带的微微网，以避免高层协议为了有效的管理组而必须与基带协议以及链路管理器直接联系。L2CAP的功能需求包括协议/管道多路技术，分割和合成，每条管道流控制和群体管理，显示L2CAP数据如何适配蓝牙协议栈，L2CAP位于连接控制协议和其它交流协议例如SDP,TCS和NEP相连接音质管道提供音频和电话应用软件和同步明晰的链接关系通常超出同时传输的限度。把L2CAP分解成它的结构上的组成部分，管道管理器提供控制平面功能并负责所有内部信号，L2CAP对等网络信号和在高低层之间的信号，它执行在第六部分描述的正式机器功能。并且应用在第4部分描述的信息版本在中继和控制流区为需要的应用软件提供每条控制流管道和选择中继。资源管理程序负责为管道管理器提供转播框架服务。中继和控制流区以及那些不需要中继和控制流的服务的数据包应用数据流，它负责调正发送和接收关于L2CAP管道在由低层界面提供的服务。L2CAP支持多路技术因为基带协议不支持任何类型领域鉴别更高层协议在原来基础上成为多元的，在多路线调整期间多路技术协议功能被用于发送连接请求到恰当的高层协议。对于数据传输合理的路线多路技术需求同多层高层实体相区别。也许会有多个高层实体用同一个协议。随着资源管理程序提供了框架传播服务，传播框架的长度由超出L2CAP范围单独得应用软件控制许多多元的应用软件会的到更好的服务如果L2CAP控制了PPU的长度。这提供如下的好处分割会允许应用软件数据单元的交往以满足反应时间的需求，当L2CAP控制数据包的尺寸的时候存储缓冲器的处理会更简单，由中继改正的错误会更有效。当一个L2CAPPPU被破坏或丢失的时候所被破坏的数据是要比使用应用软件数据单元时小。应用软件由于分割而被减弱需要使用应用数据包转换成较低层的数据包。当几个数据流从同一个L2CAP逻辑链溢出的时候用单独得L2CAP路线，每条路线需要单独得控制流。L2CAP也提供向需要控制流的文档或应用软件提供控制流服务，并且能够避免必须执行，应收于两个L2CAP层次间的变迁，在基带中作为工作的定期而不断被停止的控制流不允许分的，提供了底流控制流程表窗口，控制流的使用是L2CAP协议的一格选择部分。一些应用程序需要一格比基带能传送的更小的残留误差率L2CAP包括可选择的误差校验码和L2CAPPPUS中继在L2CAP中的错误校验软件校验错误取决于基带不真实地接受对头，取决于HEC的失败或CRC对基带包的错误校验中继模式也能保护由于在相同逻辑传播中所引起的信息包丢失错误控制器和控制流协议工作当控制流在第一次传输时将扼杀中继错误控制和中继程序的使用是可选择的。较低层限制了传输能力并且能需要与那些由L2CAP分割软件创造的不同的片断尺寸所以L2CAP以下的层次也许更细微，并且原组L2CAPPPUS只创造比每层能量的片断，在一个L2CAPPDU传播的过程中许多不同的破碎层和重组也许出现在两个相同的装置中HCI驱动器或控制器也许会包括L2CAPPPUS分割成包样的宿主机控制器且传输配置。这导致HCI数据包有效载荷传输优先地位和L2CAPPPU的附加片断，类似于链接控制器也许把L2CAPPPUS分割成基带包。这导致基带包有效载荷优先地位协议站的每一层可以通过不同大小的L2CAPPPUS碎片由一层创造的不同大小的碎片在每一相同的设备中不论在栈中PDU如被分割，接收L2CAP实体仍然交组碎片到原来的L2CAPPDU。L2CAP链接过程允许在两个蓝牙设备之间交换关于服务质量的信息，每个L2CAP执行监控被协议所应用的资源并确保服务质量优秀。12作态基于以下假设设计协议ACL合理的传输和在两个设置的L2CAP合理链接被设置用作链接管理器协议，基带提