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CompanyConfidential1©2015NSNVoLTEFundamentalWokshop/Fuzhou/2015-01-01VoLTEFundamentalFuzhou,2015-01-08VoLTEIntroductionWhatisVoLTE?•LTE(LongtermEvolution)aka4G,isthewirelesscommunicationsstandarddevelopedby3GPPstandardization,toofferhighspeedwithlowlatency.•LTEispacket-switchednetworkonly.•LTEnetworkarchitecturedoesnotincludethetraditional2G/3Gvoiceservices.•VoiceoverLTEisthesolutiontoprovidetheVoiceservicecapabilitybasedonGSMAIR.92specification.-Realtimetraffic-QualityofService-InteroperabilitytoexistingCSvoicenetwork•IPMultimediaSubsystem(IMS)enablesintegratedvoice,dataandmulti-mediaservicesinterworkingbetweendifferentaccessnetworks.IMSisbasedonSIPcallcontrolforcreating,modifying,andterminatingsessions.VoLTENetworkArchitectureOverviewCSCF（CallSessionControlFunction）：多媒体呼叫会话过程中的信令控制MGCF（MediaGatewayControlFunction）：执行IMS与CS域的互通；不同域间协议转换MGW（MediaGateway）：连接不同域的用户面；不同网络之间的编解码转换VoLTEBearerCombinationTheVoIPservicehasspecificbearercombinationrequirements：-QCI1dedicatedbearerforvoicecall.-QCI2dedicatedbearerforvideocall.-QCI5dedicatedbearerforSIPsignallingtotheIMS.-Defaultnon-GBRbearer(QCI8-9)fordatatransfer(always-on).QCIGuaranteePriorityDelaybudgetLossrateApplication1GBR2100ms1e-2VoIP2GBR4150ms1e-3Videocall3GBR5300ms1e-6Streaming4GBR350ms1e-3Realtimegaming5Non-GBR1100ms1e-6IMSsignalling6Non-GBR7100ms1e-3Interactivegaming7Non-GBR6300ms1e-6TCPprotocols:browsing,email,filedownload8Non-GBR8300ms1e-69Non-GBR9300ms1e-6VoLTESignalingOverviewSIPProtocolStackSIPPhoneEthernetInternetIPAddressRTPSIPCablePhysicalLinkNetworkApplication(Port#)TCPTransportUDPSCTPTLScodecChatSIPPhoneEthernetIPAddressRTPSIPCableTCPUDPSCTPTLScodecChatSignaling/Message(ControlPlane)Media(UserPlane)Canwetalk?(myIP/RTPPortisxxx)OK(myIP/RTPportisyyy)-TheSessionInitiationProtocol(SIP)isanapplication-layercontrol(signaling)protocolforcreating,modifying,andterminatingsessionswithoneormoreparticipantsdevelopedbyIETF–RFC3261.-SIPistransferredusingQCI5bearer.VoLTERegistration为什么要注册：-用户使用IMPU（IPMultimediaPublicIdentity）通信-建立用户当前的IP与其IMPU的对应关系-掌握用户当前的位置信息及业务能力-注册过程的鉴权与认证保证了网络的安全性VoLTERegistration1.UEattachestothenetwork,thePGWassignsIPaddressandidentifiesP-CSCFtotheterminal.2.UEsendsRegistrationRequesttoS-CSCF(viaP-CSCF)inREGISTERmessage.3.S-CSCFperformsregistrationprocedureswithHSSandacquiresuserauthenticationinformationandsendsUEachallengein401Unauthorizedmessage.4.UEcalculatestheresponseandsendsittoS-CSCFinREGISTERmessage.5.AftertheauthenticationhassucceededtheS-CSCFdownloadsandstoresservicecontrolinformationfromHSSandS-CSCFnotifiestheterminalaboutcompletedregistrationwith200OKmessage.VoLTERegistration现阶段常见问题：-终端侧未发起PDN连接请求-网络下发PDN连接拒绝VoLTECallFlow1.MOUEgeneratesanINVITErequest,whichissenttotheIMS.NotethatMOUEincludesQoSpreconditionsintheSDPwhichindicatesthatMOUEdoesnotwantMTUEtobealerteduntiltherearenetworkresourcesreservedinbothdirections.2.TheP-CSCFacknowledgestheINVITEtotheMOUEwith100Trying”messageindicatingthatthecallsetupisinprogress.3.TheSIPmethodOPTIONSallowsaIMStoqueryanotherUEoraproxyserverastoitscapabilities.Thisallowsaclienttodiscoverinformationaboutthesupportedmethods,contenttypes,extensions,codecs,etc.With200OKmessageUEanswerswithitscapabilitiestoIMS.4.TheINVITEmessagereceivedbyMTUEincludesdeclarationforusingprecondition,typeofmedia,codectouseandtheprotocolfortransportingthemediaintheSDP.Moredetailreferto3GPP24228-5f07.2.3.1/7.4.3.1VoLTECallFlow5.WhenpreconditionmechanismissupportedP-CSCFwouldsend183SessionProgresstooriginatingUEwhichthencomparestheterminatingUEcapabilitieswithitsownanddeterminesthecodectobeused.6.OriginatingUEnotifiestheterminatingUEusingPRACKtheselectedcodec.200OKisreceivedfromterminatingUE.EPSBearerActivationfollowsforbothUEs.7.TheUPDATEmessagesindicatesthatpreconditiononMOUEsideismet.8.BothterminalsconfirmthesetupofbearerwithQoSaccordingto200OKmessageandterminatingUEstartringing.9.The180RingingmessageisinitiatedfromMTtoIMSandthenIMSforwardsthe‘Ringingmessage’toMOUE.10.OncebothUEsreceive200OK,theyACKitandtheSIPsessionisestablished-voicecommunicationstarts.Precondition对于双方的UE而言，建立PDP上下文的执行过程是相互独立的。这意味着在资源被成功预留之前，根本无法保证所协商的媒体会话是否可以建立起来。因此，Precondition作用主要是为了保证在确认本地和主叫方的资源预留都已成功之前，被叫方不应振铃,以最大程度减少被叫方振铃但接听电话又失败的情况若INVITERequest消息中携带Precondition字段，表明终端支持该功能。不支持Precondition功能的呼叫流程AMRFrameTypeModeIndicationModeRequestFramecontent(AMRmode,comfortnoise,orother)000AMR4,75kbit/s111AMR5,15kbit/s222AMR5,90kbit/s333AMR6,70kbit/s(PDC-EFR)444AMR7,40kbit/s(TDMA-EFR)555AMR7,95kbit/s666AMR10,2kbit/s777AMR12,2kbit/s(GSM-EFR)8--AMRSID9--GSM-EFRSID10--TDMA-EFRSID11--PDC-EFRSID12-14--Forfutureuse15--NoData(Notransmission/Noreception)FrameTypeIndexModeIndicationModeRequestFramecontent(AMR-WBmode,comfortnoise,orother)000AMR-WB6.60kbit/s111AMR-WB8.85kbit/s222AMR-WB12.65kbit/s333AMR-WB14.25kbit/s444AMR-WB15.85kbit/s555AMR-WB18.25kbit/s666AMR-WB19.85kbit/s777AMR-WB23.05kbit/s888AMR-WB23.85kbit/s9--AMR-WBSID(ComfortNoiseFrame)10-13--Forfutureuse14--speechlost15--NoData(Notransmission/Noreception)•AMR=AdaptiveMulti-Rate，“自适应多速率编码”，主要用于移动设备的音频•AMR又称为