释放流程及异常原因分析V2.ppt

释放流程及异常释放原因分析,2016-05,概述,主要内容说明,本次主要讨论的内容：LTE业务释放类型及相应信令流程的详解；相关的counter触发定义，以及异常问题分析；通过对这些内容的梳理和讨论，能够了解LTE释放的理论知识，并且在日常KPI和Log分析方面，提供帮助。,释放流程及异常释放原因分析,主要内容,业务承载类型及业务建立过程业务释放类型及相应流程、原因E-RABreleaseUEcontextreleaseRRCconnectionrelease异常释放的触发情景详解UEinitiateddropeNBinitiateddrop异常释放relatedCounterTriggersNetwork/FieldKPI及Drops分析Summary,业务承载类型,LTE业务承载类型,LTE的业务承载类型分为默认承载、专用承载两种：默认承载：UE开机时获得承载，一定是MME发起的业务，优先级特别低，NonGBR；专用承载：一定是由PGW触发建立的；一个UE可以有不同的专用承载；,GTPvariant:EPSbearerterminationinPGW,SRB与默认、专用承载关系,业务承载类型,无线承载分类,SRBSignallingRadioBearers（SRBs）的定义是，仅用于传输RRC和NAS消息的RB（RadioBearer）；DRBDataRadioBearer，用于传输业务数据的无线承载；与S1-U承载共同组成E-RAB.分为UM、AM两种；,业务承载类型,UEcontext及E-RAB,E-RABUE至SGW之间的承载，E-RAB是指用户平面的承载，由S1-U承载和DRB（DataRadioBearer，数据无线承载）串联而成，进入LTE系统的业务数据主要通过E-RAB进行传输。因此对于LTE，业务管理主要是在E-RAB层次上进行的。一个UE可以有多个E-RAB，目前最多支持8个EPS承载（个AMDRB，3个UMDRB）.在应用上，E-RAB常出现于性能指标的统计中，例如：E-RAB建立成功率。E-RAB建立成功指eNodeB成功为UE分配了通信通道的无线资源和用户面的无线承载，所以这个指标反映了eNodeB或小区接纳业务的能力，可以用来考虑系统负荷情况。,业务承载类型,UEcontext及E-RAB,UEcontextIncludingE-RABcontext,securitycontext,roamingrestriction,UES1signallingconnectionID(s),heeNB.在源eNB的UE上下文中还包含了与漫游和接入限制有关的信息；InitialUEcontext只能由MME发起，一个UE只有一个UEcontext；一个eNBUEcontext是eNB内和一个处于激活状态的UE相关联的一个信息块。这块信息是为了维持E-UTRAN提供给这个激活态UE的服务所必须的信息；eNBUEcontext是在UE迁移到激活状态之后开始建立的；或者，eNBUEcontext是在切换目标eNB完成切换资源分配（切换准备阶段）之后开始建立的。RRCconnection层三信令连接，UE保持非IDLE的必须连接，一个UE只有一个RRCconnection，一旦连接释放，UE所有业务释放，并进入RRC_IDLE态；,LTE完整业务流程,默认承载建立信令流程（Attach）,Steps:RandomAccessInitialNASmsgNASsecurityS1initsetupRRCsec+UEcapSRB2/DRBsetupNASreply,LTE完整业务流程,RA及RRC连接建立流程,SRB0：RRCconnectionrequest、RRCconnectionsetup（消息中包含SRB1建立的相关信息）；SRB1：RRCconnectionsetupcomplete；,LTE完整业务流程,专用承载建立流程,DedicatedBearerEstablishment：E-RAB建立,释放流程及异常释放原因分析,主要内容,业务承载类型及业务建立过程业务释放类型及相应流程、原因E-RABreleaseUEcontextreleaseRRCconnectionreleaseAbnormalrelease的触发情景详解UEinitiateddropeNBinitiateddrop异常释放relatedCounterTriggersNetwork/FieldKPI及Drops分析Summary,业务释放类型,release,根据业务承载类型，业务释放过程也分为三类：E-RABreleaseThepurposeoftheE-RABReleaseprocedureistoenablethereleaseofalreadyestablishedE-RABsforagivenUE；E-RAB释放后，UE仍然可以处于ECM-CONNECTED状态；UEcontextreleaseIftheeNBwantstoremoveallremainingE-RABs,e.g.,foruserinactivity,theUEContextReleaseRequestprocedureshallbeusedinstead.当UE回到ECM-IDLE状态时，MME向eNodeB发UECONTEXTRELEASE消息。收到这条消息后，eNodeB删除eNBUEcontext。MME继续保留MMEUEcontext.,业务释放类型,release,根据业务承载类型，业务释放过程也分为两类：RRCconnectionreleaseThepurposeofthisprocedureistoreleasetheRRCconnection,whichincludesthereleaseoftheestablishedradiobearersaswellasallradioresources；RRC连接释放后，UE进入RRC_IDLE状态。,E-RABrelease,释放类型：E-RABrelease,根据3GPP定义(3GPPTS36.413)，E-RABrelease过程分为两大类：ENodeBInitiatedMMEInitiatedE-RAB管理的相关信息都embed在context管理信令中。,MMEInitiated,ENodeBInitiated,释放流程信令详解,E-RABrelease：MMEInitiated,E-RABreleasecommand消息内容：shallcontaintheinformationrequiredbytheeNBtoreleaseatleastoneE-RABintheE-RABToBeReleasedListIE.IfaNAS-PDUIEiscontainedinthemessage,theeNBshallpassittotheUE.E-RABToBeReleasedListIE.theUEAggregateMaximumBitRateIE.E-RABreleaseresponse消息内容：-AlistofE-RABswhicharereleasedsuccessfullyshallbeincludedintheE-RABReleaseListIE.-AlistofE-RABswhichfailedtobereleased,ifany,shallbeincludedintheE-RABFailedtoReleaseListIE.,释放流程信令详解,E-RABrelease：MMEInitiated,eNB收到E-RABRELEASECOMMAND后，eNB将会释放被请求的ERABs.对于每一个要释放的E-RAB，eNB会释放其相应的DRB和空口资源。TheeNBshallpassthevaluecontainedintheE-RABIDIEreceivedfortheE-RABtotheradiointerfaceprotocolforeachDataRadioBearertobereleased.TheeNBshallreleaseallocatedresourcesonS1fortheE-RABsrequestedtobereleased.,Networktriggered(fromDeleteBearer),释放流程信令详解,E-RABrelease：eNBInitiated,E-RABRELEASEINDICATION消息内容：TheE-RABRELEASEINDICATIONmessageshallcontainatleastoneE-RABreleasedattheeNB,intheE-RABReleasedListIE.UponreceptionoftheE-RABRELEASEINDICATIONmessagetheMMEshallnormallyinitiatetheappropriatereleaseprocedureonthecorenetworksidefortheE-RABsidentifiedintheE-RABRELEASEINDICATIONmessage.InteractionwithUEContextReleaseRequestprocedure:IftheeNBwantstoremoveallremainingE-RABs,e.g.,foruserinactivity,theUEContextReleaseRequestprocedureshallbeusedinstead.,释放流程及异常释放原因分析,主要内容,业务承载类型及业务建立过程业务释放类型及相应流程、原因E-RABreleaseUEcontextreleaseRRCconnectionreleaseAbnormalrelease的触发情景详解UEinitiateddropeNBinitiateddrop异常释放relatedCounterTriggersNetwork/FieldKPI及Drops分析Summary,UEcontextrelease,释放类型：UEcontextrelease,根据3GPP定义(3GPPTS36.413)，UEcontext过程同样分为两大类：ENodeBInitiatedMMEInitiatedThisprocedureisusedtoreleasethelogicalS1-APsignallingconnection(overS1-MME)andallS1bearers(inS1-U)foraUE.TheprocedurewillmovetheUEfromECM-CONNECTEDtoECM-IDLEinboththeUEandMME,andallUErelatedcontextinformationisdeletedintheeNodeB.,UEcontextrelease,释放的触发条件UEContextReleaseRequest,该信令，使基站可以根据E-UTRAN的需要，向MME请求UE-associatedS1链接的释放；ENodeB发起的Contextrelease情况：Normalrelease：“UserInactivity”，CSFallbacktriggered，UENotAvailableforPSService，Inter-RATRedirection，TimeCriticalHandover，HandoverCancelled，“Detach”Abnormalrelease：“RadioConnectionWithUELost”,“CSGSubscriptionExpiry”,“Redirectiontowards1xRTT”，UnspecifiedFailure，OLessactiveUeswhichnetworkhastohandle;Fastgoingtoinactivityhasdrawbackoflongerconnectionsetuptime(moretransitionsidletoconnected).,释放流程信令详解,UEcontextrelease：ENodeBInitiated,释放流程信令详解,UEcontextrelease：MMEInitiated,TheUECONTEXTRELEASECOMMANDmessageshallcontaintheUES1APIDpairIEifavailable,otherwisethemessageshallcontaintheMMEUES1APIDIE.TheMMEprovidesthecauseIEsetto“LoadBalancingTAURequired”intheUECONTEXTRELEASECOMMANDmessagesenttotheeNBforallloadbalancingandoffloadcasesintheMME.MMEUES1APisreleasedwhentheS1connectionisreleased(nexttimeanewvalueisassigned)eNBUES1APisreleased,释放流程信令详解,UEcontextrelease：MMEInitiated,UponreceptionoftheUECONTEXTRELEASECOMMANDmessage,theeNBshallreleaseallrelatedsignallinganduserdatatransportresourcesandreplywiththeUECONTEXTRELEASECOMPLETEmessage.IncaseofeNBsupportingL-GWfunctionforLIPAoperation,theeNBshallalsoreleasethenodeinternaltunnelresources.,释放流程信令详解,UEcontextrelease：MMEInitiated,释放流程信令详解,UEcontextrelease：MMEInitiated,释放流程及异常释放原因分析,主要内容,业务承载类型及业务建立过程业务释放类型及相应流程、原因E-RABreleaseUEcontextreleaseRRCconnectionreleaseAbnormalrelease的触发情景详解UEinitiateddropeNBinitiateddrop异常释放relatedCounterTriggersNetwork/FieldKPI及Drops分析Summary,RRCconnectionrelease,释放类型,根据3GPP定义(3GPPTS36.331)，E-UTRANinitiatestheRRCconnectionreleaseproceduretoaUEinRRC_CONNECTED：RRCconnectionreleaseThepurposeofthisprocedureistoreleasetheRRCconnection,whichincludesthereleaseoftheestablishedradiobearersaswellasallradioresources.RRCconnectionreleaserequestedbyupperlayersThepurposeofthisprocedureistoreleasetheRRCconnection.AccesstothecurrentPCellmaybebarredasaresultofthisprocedure.,RRCconnectionrelease,释放原因,ThereleaseoftheRRCconnectionisinitiatedbyE-UTRAN.Theproceduremaybeusedtore-directtheUEtoanotherfrequencyorRAT.InexceptionalcasestheUEmayaborttheRRCconnection,i.e.movetoRRC_IDLEwithoutnotifyingE-UTRAN.,释放流程及异常释放原因分析,主要内容,业务承载类型及业务建立过程业务释放类型及相应流程、原因E-RABreleaseUEcontextreleaseRRCconnectionreleaseAbnormalrelease的触发情景详解UEinitiateddropeNBinitiateddrop异常释放relatedCounterTriggersNetwork/FieldKPI及Drops分析Summary,Calldrop,WhoInitiatesDrops,UE,MMEoreNB?,UEcan”initiateadrop”bystartingRRCConnectionRe-establishmentNote:besidesRLFalsoothercausescantriggerRRCConnRe-EstablishmenteNBcaninitiateabnormalS1+RRCreleaseduetoRadionetworklayerproblem(TAtimer,RLF,PDCCHOrderfailure)Transportnetworklayerproblem(GTP-Uerror,Trelocexpiry,PathSwitchproblem)OtherabnormalcauseMMEcaninitiateabnormalS1+RRCreleaseduetoRadionetworklayerproblemOtherabnormalcause,UEinitiateddrop,RLF,WhenUEisinRRC_CONNECTEDandRRCsecurityisactive,itcantriggerRRCConnectionRe-establishmentuponT310expiryuponreachingthemaximumnumberofULRLCretransmissionsuponhandoverfailure(T304expiry)uponnon-HOrelatedrandomaccessproblemIfsuccessful,RRCConnRe-EstablishmentreconfiguresSRB1toresumedatatransferofRRCmsgsre-activatesRRCsecuritywithoutchangingalgorithmsNOTE:DRBshouldbere-configuredafterSRB1NOTE:ifUEisinRRC_CONNECTEDwhileRRCsecurityisnotactive,UEgoestoRRC_IDLE,performscellreselectionandTAU,UEinitiateddrop,RLFduetoT310ExpiryatUE,UEinitiateddrop,RLFduetoMaximumULRLCRe-TxReached,fromRRCConnectionReconfiguration:drb-ToAddModListdrb-ToAddModListvalue1drb-Identity:1rlc-Configamul-AM-RLCt-PollRetransmit:ms40pollPDU:p32pollByte:kB25maxRetxThreshold:t8,UEinitiateddrop,RLFduetoHOFailure,fromRRCConnectionReconfiguration:mobilityControlInfotargetPhysCellId:33t304:ms1000newUE-IdentityBin:14EB(=5355),UEinitiateddrop,RLFDuetoNon-HORandomAccessFailure,“Non-HOrandomaccess”meansPDCCHorder-triggeredRARandomAccessSchedulingRequest,释放流程及异常释放原因分析,主要内容,业务承载类型及业务建立过程业务释放类型及相应流程、原因E-RABreleaseUEcontextreleaseRRCconnectionreleaseAbnormalrelease的触发情景详解UEinitiateddropeNBinitiateddrop异常释放relatedCounterTriggersNetwork/FieldKPI及Drops分析Summary,eNBinitiateddrop,RLF,eNBcandropthecallduetofollowingtriggerseNB-detectedradiolinkproblemsPUSCHRLFCQIRLFAck/NackRLFPDCCHOrderfailureSRSRLFTAtimerexpiryMaximumRLCretransmissionsexceededGTP-Ufailure,eNBinitiateddrop,RadioLinkProblemDetectionateNB,eNBradiolinkproblemdetectionmechanismsareNSN-internallyspecifiedMultiplemethods(called“linkmonitors”)aredefinedtodetectaradiolinkproblemintheeNB.Whenonelinkmonitordetectsaproblem,itisreallyaradiolinkproblemevenifotherlinkmonitorshavenotyetindicatedanything.Eachlinkmonitorhasitsinternalcriteriatodecidewhenradiolinkproblemisflaggedandde-flagged(radiolinkrecovers).IftheRLPpersistslongerthanT_RLF,RRC+S1releaseistriggeredT_RLF=t310+t311(eNB-internaltimer)Linkmonitors:UplinkPUSCHDTXdetectionforscheduleduplinkdataCQIDTXdetectionforperiodicCQIreportsinPUCCHandPUSCHUplinkAck/NackDTXdetectionfortransmitteddownlinkdataPDCCHOrderRLFSRSDTXdetection(TD-LTE),eNBinitiateddrop,1.PUSCHRLF:RlsCause_PuschRlf_ON,WhenUEisscheduledforPUSCHtransmission,eNBexpectstoreceiveULtransmissiononthescheduledPRBsIfsignalfromUEcannotbedetectedatall,PUSCHDTXisdeclaredNOTE:ThecasewhereULTBSisreceivedbutitfailsCRCcheckisnotDTX(itsaNACK)DTXPUSCHindicationisprovidedbytheULphysicallayer.TheresultisreceivedbyLTEMACinreliableULtransmissionFlagparameter.Bothcounter-basedandtimer-basedRLFdetectionissupportedTimer-basedPUSCHRLFdetection:If“DTX“isreceivedonthePUSCHforaconfigurableperiodoftime(rlpDetMaxTimeUl),PUSCHRLFissetonCounter-basedPUSCHRLFdetection:If“DTX“isreceivedonthePUSCHforaconsecutivenumberoftimes(rlpDetMaxNoUl),PUSCHRLFissetonTherecoveryoftheradiolinkisindicatedwhenforaconfigurablenumberofcontiguousULresourceassignmentsdataisdetectedonPUSCH(ACKorNACKreceived).DefinedbyparameterrlpDetEndNoUl.,eNBinitiateddrop,1.PUSCHRLF:RlsCause_PuschRlf,Counter-basedRLFDetectionExample,T_RLF=T310+T311,32,vendor-fileparametersinthisexample:,eNBinitiateddrop,2.PeriodicCQIRLF:RlsCause_CqiRlf_ON,TheeNBsupportsCQIDTXdetectionforperiodicCQIreportsonPUCCHandPUSCH.IfMAClayerreceivesnCqiDtxconsecutivereportsfromULPHY,theMACdeclaresCqiRLF_ONIftheMAChassetCqiRLF_ONforaspecificUEandnCqiRecconsecutiveCQIreportsareagaindetectedsuccessfullyforthatUE,theMACsetsCqiRLF_OFFTheparametersnCqiDtxandnCqiRecareinthevendor-specificparameterfileForbothPUSCHandPUCCHtheperiodicCQIisencodedusingaReedMullerblockcodeandcomesalongwithoutanyCRC.Hence,theULPHYindicatesaDTXdetectionforperiodicCQIreportsonPUCCHorPUSCHwheneverareportisconfiguredbutnoreliabletransmissionfromtheUEcouldbedetected.SotheoutputofthedetectorshallbeeitherthedetectedCQIreportoraDTXindication.NOTE:CQI_RLFdetectiondoesnotapplytoaperiodicCQIreportonPUSCH,eNBinitiateddrop,2.PeriodicCQIRLF:RlsCause_CqiRlf,Example,61,vendor-fileparametersinthisexample:,T_RLF=T310+T311,eNBinitiateddrop,3.Ack/NackRLF:RlsCause_AckNackRlf_ON,AfterDLscheduleddata,eNBexpectsHARQACKorNACKonPUCCHorPUSCHatknownULTTITimer-basedACK/NACKRLFdetection:IfACK/NACK“DTX“isreceivedforaconfigurableperiodoftime(rlpDetMaxTimeDl),ACK/NACKRLFissetonCounter-basedACK/NACKRLFdetection:IfACK/NACK“DTX“isreceivedforaconsecutivenumberoftimes(rlpDetMaxNoDl),ACK/NACKRLFissetonTherecoveryoftheRLFisindicatedwhenforaconfigurablenumberofcontiguousACK/NACKopportunitiesACKorNACKisdetectedonPUSCHorPUCCH(noDTX).DefinedbyparameterrlpDetEndNoDl.,eNBinitiateddrop,4.PDCCHOrderRLF,IfthereDLdataineNBbufferandUEisout-of-sync,UEmustbebroughtbacktoin-sync(timealigned)withaRAprocedurebeforeDLdatacanbesentSignalingofdedicatedRApreambleviaPDCCH(so-calledPDCCHorder)isdoneusingDCIformat1AIncasethatPDCCHorderfailsforaUE(i.e.,notransmissionofassigneddedicatedpreambledetectedbyeNodeB,ornomsg3transmission)thePDCCHordershallberepeatednoRepPdcchOrdertimes(RnotifyRRClayertoreleasePUCCH/SRS;clearanyconfigureddownlinkassignmentsanduplinkgrants3GPPTS36.331:UponreceivingaPUCCH/SRSreleaserequestfromMAClayer,theUERRCshall:releaseperiodicCQIreportingconfig,ieitstopsCQIreportingonPUCCHreleaseSchedulingRequestConfig,eNBinitiateddrop,In-Sync,Out-Of-SyncHandlinginRL30,ParameterLNCEL/applyOutOfSyncStatedefineshoweNBhandlesTAexpiryextendedDrxOnly:onlyUEsbeingconfiguredwithextendedsettingsforthelongDRXcyclearenotdroppedifTAtimerexpires(default)allDrx:allUEsbeingconfiguredforDRXprovidedthatappliedDRXprofileallowsarenotdroppedifTAtimerexpiresallUEs:allUEsindependentlyofDRXconfigurationprovidedthatbearercombinationallowsarekeptRRCConnectedevenifTAtimerexpires.IfDRXisnotusedatall,thensettingallUEsshouldbeusedtopreventeNBdropsduetoTAtimerexpiry,eNBinitiateddrop,In-SyncNormalCase,ProceduredescribeshowanUEgetsbackintoULsynchronizationfromastateinwhichthetimealignmenthasbeenlosteNBdetectsthatthetimealignmentoftheUEisULout-of-sync(e.g.expirationoftimealignmenttimer)UEalsodetectsout-of-sync(sametrigger)andreleasesresourcesonPUCCHforCQIreportingandschedulingrequestIfeNBdetectsDLdata(eitherdatatrafficorRRCsignalling)eNBsendsaPDCCHorderforRAproceduretoUE(DCI1Awithspecificcodepoint;preferablynon-contentionbasedRAdependingonpreambleavailability)UEstartsarandomaccessprocedureeNBrecognizeswhenrandomaccessoftheUEwassuccessfulandUEULtimealignmentisback“in-sync”IfUEdetectsULdata(eitherdatatrafficorRRCsignalling):UEstartsarandomaccessprocedure(contention-based)eNBrecognizeswhenrandomaccessoftheUEwassuccessfulandUEULtimealignmentisback“in-sync”eNBtriggerstheRRCprocedureRRCConnectionReconfigurationtoconfigure(again)thePUCCHresourcesforCQIreportingandschedulingrequestSameresourceusedforsimplificationbutcouldbeoptimizedoptionallyNote:theRRCmessageRRCConnectionReconfigurationCompleteisalreadysentusingtheconfiguredPUCCHresourcesforschedulingrequest.,eNBinitiateddrop,In-SyncFailureCase,ProceduredescribeshoweNBdetectsthatanUEhasbeenlosttriggeredbydownlinktrafficeNBdetectsthatthetimealignmentoftheUEis“out-of-sync”(e.g.expirationoftimealignmenttimer)UEdetectsalsothatthetimealignmentisout-of-syncandreleasesitsPUCCHresourcesforCQIreportingandschedulingrequestand/orUEdetectsaradiolinkfailureandmovestoRRC_IDLEIfeNBdetectsDLdata(eitherdatatrafficorRRCsignalling)eNBsendsaPDCCHorderDCI1AtoUE(mayincludeseveralre-tries)UEwillnotrecognizethisPDCCHorderbecauseithasgonetoRRC_IDLEeNBrecognizesthattherandomaccessoftheUEwasnotsuccessful(UEdoesnotsendanyrandomaccesspreamble)andthatthe“in-sync”handlinghasfailedThiseventishandledasanewtriggerfortheradiolinkfailureprocedureeNBstartsasupervisiontimerT-RLFandtriggersUEContextReleaseaftertimerexpirationNote:byusingthesupervisiontimer,UEisabletoreturntocellviatheRRCConnectionReestablishmentprocedure,eNBinitiateddrop,UserInactivityDetectionDuringOut-Of-Sync,ProceduredescribeshoweNBhandlesanUEwhosetimealignmentisout-of-syncandwhoseinactivitytimerhasexpiredeNBdetectsthatthetimealignmentoftheUEis“out-of-sync”(e.g.expirationoftimealignmenttimer)TheinactivitytimerfortheUEexpires.Inthemeantime,UEmaystillbeRRC_CONNECTEDormayhavegonetoRRC_IDLEsilentlyeNBchecksthereachabilityoftheUEbysendingthePDCCHorder(DCI1A)IfUEperformsarandomaccesseNBrecognizesthatthisisanormal“userinactivity”caseeNBsendstheRRCmessageRRCConnectionReconfigurationtoconfigurePUCCH/SRSresourceseNBsendsthemessageUECONTEXTRELEASEREQUESTtoMMEwithcause“UserInactivity”IfMMEstartstheUEContextReleaseprocedureeNBsendstheRRCmessageRRCConnectionReleasetoUEandreleasestheUEcontext.IfMMEdoesnotstarttheUEContextReleaseprocedureeNBkeepsthecurrentconfiguration.Note:thismayhappenifnewDLdataarrive-eitherdatatrafficorS1APsignallingIfeNBdoesnotrecognizeanyrandomaccessbytheUEeNBrecognizesthatthisisaRLFtrigger.eNBstartsimmediatelytheUEContextReleaseprocedureforRLF,eNBinitiateddrop,RRC+S1ReleaseafterTATimerExpiryateNBWhenOut-Of-SyncHandlingNotUsedforUE,NOTE:TAout-of-synccausesimmediaterelease(noT_RLFinvolved),eNBinitiateddrop,TATimerExpiryateNB,User-ConfigurableParameters,Outdated:Alwayscheckthecurrentvalues(defaultsandtheactualused)oftheeNBswversioninuse.,eNBinitiateddrop,TATimerExpiryateNB,VendorParameters,Outdated:Alwayscheckthecurrentvalues(defaultsandtheactualused)oftheeNBswversioninuse.,eNBinitiateddrop,RLCLayerSTATUSPollingMechanism,RLClayerretransmissionsonlyinRLCacknowledgedmodeRLCAMtransmitterrequestsaSTATUSPDUfromRLCreceiver(setspollbitoninRLCheader)AfterthenumberofbytestransmittedsincepreviouspollexceedsthevalueofamRlcPBTab3ulPollByte(uplink,uecat3)oramRlcPBTab3dlPollByte(downlink,uecat3),orAfterpollPduRLCPDUshavebeentransmittedsincepreviouspollinthelastdataPDUintheRLCtransmitbufferTheRLCAMreceiverrespondstopollingrequestbytransmittingaSTATUSPDUwhichacknowledgessuccessfullyreceivedPDUsandalsoselectivelynacksunsuccessfullyreceivedPDUs.RLCreceiveralsosendsSTATUSPDUiftReordtimerexpires.RLCreceiverwillnotsendSTATUSPDUmoreoftenthanintervaldefinedbyparametertProhib.NOTE:defaultPDDBsettingstProhib=50msandtReord=50ms.IfRLCtransmitterreceivesnoSTATUSPDUwithintPollretr,anewpollrequestalongwithunacknowledgeddatawillbesenttoRLCreceiverRLCAMwindowsizeisfixedto512RLCPDUs(segmentsofanRLCPDUarecountedasonePDU).,eNBinitiateddrop,RLCLayerARQMechanism,RLCtransmitterwillretransmitalldatathatisnackedintheSTATUSPDUMaximumnumberofULandDLRLCretransmissionsisdefinedbyvendorparameterdrbAmMxRtxTh(default=16),eNBinitiateddrop,ReleaseduetoMaximumNumberofDownlinkRLCRetransmissions(eNB-triggered),VendorparameterdrbAmMxRtxTh(default=16)SRB1orSRB2:aftermaxRLCretransmissionshasbeenreachedeNBreleasestheUEimmediately(S1+RRCrelease).DRB:aftermaxRLCretransmissionshasbeenreachedeNBstartsatimerT_RLC(T311+200ms)t