现代通信网络

.,现代通信网络ModernTelecommunicationNetwork,Lecture3(CS)电路交换与软交换北邮软件学院：陈候武Chenhouwu电话.,CommunicationNetworks【通信网络的分类】,CommunicationNetwork,SwitchedCommunicationNetwork,VirtualCircuitNetwork:MPLS,BroadcastCommunicationNetwork广播，电视，卫星,PacketSwitch(PS)-分组交换,DatagramNetwork:Internet:IP因特网,Circuit-Switched(CS)-电话,.,通信业务网(ServiceNetwork)：分类：,.,SwitchedNetwork：【通信交换网络】,.,NodeSwitching（节点交换）,Anode(switch)inacircuitswitchingnetwork,.,Nodes【交换节点】,Nodesmayconnecttoothernodesonly,ortostationsandothernodesNodetonodelinksusuallymultiplexed【复用】NetworkisusuallypartiallyconnectedSomeredundantconnections【冗余连接】aredesirableforreliabilityTwodifferentswitchingtechnologiesCircuitswitching【电路交换】Packetswitching【分组交换】,.,CS:CircuitSwitch电路交换【Overview】,.,CS:CircuitSwitching【电路交换】,Dedicatedcommunicationpathbetweentwostations【专用/独享的通信通道】Threephases【呼叫建立：3个阶段】EstablishTransferDisconnectMusthaveswitchingcapacityandchannelcapacitytoestablishconnectionMusthaveintelligencetoworkoutrouting必须具有智能以对呼叫进行选路,.,CircuitSwitching-Applications,InefficientChannelcapacitydedicatedfordurationofconnectionIfnodata,capacitywastedSetup(connection)takestimeOnceconnected,transferistransparentDevelopedforvoicetraffic(phone:电话网),.,CS：PSTN网络结构,PSTNPublicSwitchedTelephoneNetworkUsesdigitaltrunksbetweenCentralOfficeswitches(CO)UsesanaloglinefromphonestoCO,DigitalTrunks数字中继,Analogline,CentralOffice,CentralOffice,.,PSTN:PublicCircuitSwitchedNetwork,.,CS:Components【网络组成】,Subscriber【用户：电话】DevicesattachedtonetworkSubscriberline【用户连线】LocalLoop【本地环路】Subscriberloop【用户环路】ConnectiontonetworkFewkmuptofewtensofkmExchange/Switch【交换机】SwitchingcentersEndoffice-supportssubscribersTrunks【中继线】BranchesbetweenexchangesMultiplexed【复用】,.,LegacyDigitalCircuitSwitch,CentralizedIntelligenceProprietaryCodeProprietaryservicedeploymentVeryexpensive,.,CircuitSwitchElements【电路交换组成】,.,CircuitSwitchingConcepts,DigitalSwitch【数字交换】ProvidetransparentsignalpathbetweendevicesNetworkInterface【网络接口】ControlUnit【控制单元】EstablishconnectionsGenerallyondemandHandleandacknowledgerequestsDetermineifdestinationisfreeconstructpathMaintainconnectionDisconnect,.,NodeswitchingSystem:,.,CS：SPC:电话数字程控交换机模块,.,CS:CirtuitSwitch【SwitchFabric：交换矩阵】,.,SwitchFabric:MxN,.,SwitchFabric:Mathgraphpresentation,Ainputmaysetuponeconnection(1,3,6,7),multipleconnections(4),ornoconnection(2,5,8).,.,SwitchFabric:数学模型,Inputset:T=0,1,2,M-1Outputset:R=0,1,2,N-1Definition:tTandrRt，RtR，then:c=|t,Rt|isaconnection.tisstartpointoftheconnection,rRtistheendpoint.ifrRt,Rtcontainsonlyoneitem,thisconnectionispointtopoint.ifrRt,Rtcontainsmorethanoneitem,thisconnectionispointtomulti-point.Multicast:RtR;Broadcast:Rt=Rconnectionsetinswitchfabric:C=|c0,c1,c2,|,.,SwitchFabric:连接函数,连接函数:inputlink:x(0=x=M-1)Outputlinkf(x)(0=f(x)=N-1).例如：连接函数:(x2,x1,x0)=x1,x0,x2(000)=000,(001)=010,(010)=100,(111)=111,.,SwitchingFabric:TimeDivision,Time-slotswitchingisadevice,whichbuffersmincomingtime-slots,arrangesnewtransmitorderandtransmitsntime-slotsUsedinPacketswitchandATMaswellasdigitaltelephoneswitch,.,SwitchingFabric:SpaceDivision,.,Time/SpaceDivisionMultiplexing,TIMESWITCH,TIMESWITCH,TIMESWITCH,TIMESWITCH,TIMESWITCH,TIMESWITCH,SPACESWITCH,.,CS：BlockingorNon-blocking,Blocking【阻塞】AnetworkisunabletoconnectstationsbecauseallpathsareinuseAblockingnetworkallowsthis【网络允许Blocking】UsedonvoicesystemsShortdurationcallsNon-blocking【无阻塞】Permitsallstationstoconnect(inpairs)atonceUsedforsomedataconnections,.,SwitchingFabric:Blocking,如果：I0正在连续到O0,问：I1可以连接到O0orO1?结果：内部阻塞,.,解决方案：MultistageSwitch,ReducednumberofcrosspointsMorethanonepaththroughnetworkIncreasedreliabilityMorecomplexcontrolMaybeblocking,.,解决方案：两级交换矩阵,.,解决方案：ThreeStageSwitch,x,x,x,x,.,CS：TST交换矩阵-实例：,TST-TimeswitchandSpaceswitch(1)T接线器:Auserinfo.Occupyatimeslot8bitscode.,.,（3）TST接线器512x512TimeSlots,.,CS:电路交换【PSTN:TrunkMultiplexing】,.,CO1CO2:TruckMultiplexing,.,Mux,.,.,.,.,.,1,1,1,1,1,2,2,2,.,64kb/svoicechannel,t4t3t2t1,2Mb/soutputsignal,同步时分复用：SynchronousTDM,.,E1:2Mb/sframestructure,0,1,2,314,15,16,1730,31,0,1frame-256bits-125ms,FrameAlignmentWord,3.9us,NetworkSignaling,Channels1to15,Channels16to30,.,MUXMUXMUXMUXMUX,1234,1234,E1E1E1E1,E2E2E2E2,E5,2.0488.44834.368139.264561.480MbpsMbpsMbpsMbpsMbps,CH2,CH1,CH32,E31,E32,E33,E34,E41E42E43E44,ITU-TE1DIGITALMULTIPLEXINGHIERARCHY,E1E2E3E4E5,.,ANSI：T1-T-carriersystem1.544M,Eachframecarriesonesample(8bits)foreach24channels,plusoneframingbit=193bits193*8000(samples/sec)=1.544Mbit/sec=T-1,Channel1,Channel2,Channel3,Channel24,Channel1,Channel2,Channel3,Channel24,FramingBit,1D4Frame,TDM,.,ANSI:T1/DS1FrameStructure-1.544Mbps,Every8thbitusedforsignalinginefficient,0,1,2,21,22,620,23,1frame-193bits-24channels,Bit8-reservedforsignaling,Framingbit,3,4,5,0,1,Bits1-7Payload,.,ANSI:DIGITALMULTIPLEXINGHIERARCHY,T1T2T3T4T5,MUXMUXMUXMUXMUX,12T313T324T335T346T357T36,1234,12,T1T1T1T1,T2T2T2T2T2T2T2,T4T4,T5,CH1CH2CH24,24,VF,1.5446.31244.736274.176560.160MbpsMbpsMbpsMbpsMbps,.,.,StatisticalTDM【统计时分复用】,InSynchronousTDMmanyslotsarewastedStatisticalTDMallocatestimeslotsdynamicallybasedondemandMultiplexerscansinputlinesandcollectsdatauntilframefullDatarateonlinelowerthanaggregateratesofinputlines,.,StatisticalTDMFrameFormats,.,StatisticalTDMvSynchronousTDM,StatisticsTDMdividesadatalinkintosomelogicsub-channel,.,StatisticalTDMvSynchronousTDM：Formats,.,StatisticalTDM举例：HDLC,HDLC：HighLevelDataLinkControlSynchronoustransmissionAlltransmissionsinframesSingleframeformatforalldataandcontrolexchanges,.,HDLC：FrameStructure,Flag,Address,Control,Information,FCS,Flag,8bits,8extendable,8/16,variable,8,16/32,trailer,FrameCheckSum,.,HDLC：AddressField,IdentifiessecondarystationthatsentorwillreceiveframeUsually8bitslongMaybeextendedtomultiplesof7bitsLSBofeachoctetindicatesthatitisthelastoctet(1)ornot(0)Allones(11111111)isbroadcast,.,CS:电路交换【PSTN:Signaling信令】与【CallControl：呼叫控制】,.,CS:PSTN控制信令与呼叫控制各阶段,Eachconversationrequiresachannelswitchedthroughoutthenetwork呼叫请求：Callrequest；呼叫建立：Callestablished;呼叫接收,1.Callisrequested,3.Channelisestablished,2.Callisaccepted,.,PSTN,CS:PSTN电话号码编码方案,3digitsareacode【区域码】+3digitsofficecode【局码】+4digitsphone【本局随机码】EachLocalExchangeCarrierswitch(LEC：本地交换局)areassignedablockofatleast10,000numbersTheInter-ExchangeCarrier(IXC：汇接局)switchesareresponsiblefortransmittinglongdistance,IXC212,LEC555,4210,(212)5554210,.,CS:PSTNCallRouting-1,InternationalNumberingPlanE.164【国际电话号码方案】useprefix-baseddialing,408,5644,555,PSTN,SS7,.,CS:PSTNCallRouting-2,ThefirstLEC【本地交换机】receivesacall,seeing1asthefirstdigitandthenpassesthecallontotheIXCswitch.TheIXCthenroutesthecall,viaSS7,totheremoteIXCresponsiblefor212.【远端的212中继局】The212IXClooksattheofficecodeandpassesitontothe555LECswitch.【515本地局】The555LECswitchthenchecksthestationcodeandsignalstheappropriatephone,.,Signaling:ControlFunctions【控制功能】,AudiblecommunicationwithsubscriberTransmissionofdialednumberCallcannotbecompletedindicationCallendedindicationSignaltoringphoneBillinginfoEquipmentandtrunkstatusinfoDiagnosticinfoControlofspecialistequipment,.,PSTN：用户信令,Usesloop-startsignaling【环路信令】Indicatesifthephoneison-hookoroff-hook,orgeneratesring-toneonphone.Closescircuitwhenphoneisoff-hookUsestwowires,tipandring,Tip,FXS,Ring,.,SwitchtoSwitchSignaling：【中继信令】,SubscribersconnectedtodifferentswitchesOriginatingswitchseizesinterswitchtrunkSendoffhooksignalontrunk,requestingdigitregisterattargetswitch(foraddress)Terminatingswitchsendsoffhookfollowedbyonhook(wink)toshowregisterreadyOriginatingswitchsendsaddress,.,中继信令：基本呼叫流程：,.,中继信令：呼叫控制：FSMFiniteStateMachine(有限状态机主叫方),.,PSTN:SignalingMethods【中继信令分类】,CASChannelAssociatedSignaling【随路信令】SignalingassociatedwitheachchannelhasfixedplacementwithinframeTraditionalT-1andE-1forvoiceusesCASCCSCommonChannelSignaling【共路信令】Signalingpassedviamessagingprotocol,out-of-bandsignalingCancarryawidevarietyofmessages,e.g.Caller-IDetcISDNusesaCCS-basedprotocolQ.931Q.SIGwhichistypicallyusedforPBX-to-PBXconnectivity,andisavariantofQ.931,isCCD-basedSS7istheCCS-basedprotocolusedinthePSTN,i.e.betweenCOs,.,Drawbacks【缺点】ofInCAS,LimitedtransferrateDelaybetweenenteringaddress(dialing)andconnectionOvercomebyuseofcommonchannelsignaling,.,CASv.CCS,.,SS7：SignalingSystemNumber7,SS7：CommonchannelsignalingschemeISDNOptimizedfor64kdigitalchannelnetworkCallcontrol,remotecontrol,managementandmaintenanceReliablemeansoftransferofinfoinsequenceWilloperateoveranalogandbelow64kPointtopointterrestrialandsatellitelinks,.,PSTNSS7/SignalingSystem7,SS7messagesareexchangedbetweennetworkelementsonbi-directionalchannels(typicallyT1lines)calledsignalinglinks.,TrunkLines,SSP(CO),SSP(CO),STP,SS7,STP,T-1,T-1,.,PSTNSS7SignalingPoints,SS7networkiscriticaltocallprocessing,SCPsandSTPsareusuallydeployedinmatedpairconfigurationsinseparatephysicallocationstoensurenetwork-wideserviceintheeventofanisolatedfailure.Linksbetweensignalingpointsarealsoprovisionedinpairs.Trafficissharedacrossalllinksinthelinkset.Ifoneofthelinksfails,thesignalingtrafficisreroutedoveranotherlinkinthelinkset.,SS7Links,STP,STP,SSP,SSP,SCP,SCP,SS7Links,TrunkLinks,.,SS7：网元功能,SSP(ServiceSwitchingPoint)SSPsareswitchesthatoriginate,terminate,ortandemcalls.AnSSPsendssignalingmessagestootherSSPstosetup,manage,andreleasevoicecircuitsrequiredtocompleteacall.AnSSPmayalsosendaquerymessagetoaSCPtodeterminehowtorouteacall.【智能网功能】ThefunctionalityoftheSSPisusuallyintegratedintotheCO(CentralOfficeswitch：终端局).STP(SignalTransferPoint)【信号转接点】NetworktrafficbetweensignalingpointsmayberoutedviaapacketswitchcalledanSTP.AnSTProuteseachincomingmessagetoanoutgoingsignalinglinkbasedonroutinginformationcontainedintheSS7message.AnSTPcanalsoactasafirewalltoscreenSS7messagesexchangedwithothernetworks.SCP(ServiceControlPoint)【信号控制点】AnSCPisacentralizeddatabasethattellsanSSPhowtorouteacall(e.g.,atoll-free1-800/888call).ItsendsaresponsetotheoriginatingSSPcontainingtheroutingnumber(s)associatedwiththedialednumber.,.,SS7：信令功能,SS7在移动网络中漫游功能的应用,.,CS:电路交换【PSTN:电话网组网原理】,.,CS：AT传统网络业务控制对象和业务应用单元被封闭在业务交换网内,同时用户接口和网络接口的不同使用户的业务能力受限;,.,CS:Softswitch:PSTN-IPArch,SS7SignallingGateway,PSTNTrunks,MediaGateway(Trunking),PSTNOriginatingorTandemSwitch(es),SS7Network,MediaGatewayController,MediaGateway(Trunking),RTP/UDP/IPStream,Megaco,SS7SignallingGateway,Megaco,MediaGatewayController,PSTNTrunks,VoIPTerminals,PSTNOriginatingorTandemSwitch(es),SS7Network,M3UA/SCTP,SS7,SS7,TDM,TDM,M3UA/SCTP,SIP-T,.,CS：软交换结构网元组成,MediaGatewayController（MGC）：Softswitch:SignalingGateway【信令网关】MediaGateway【媒体网关】TrunkinggatewayLineGatewayResidentialGateway软交换的新业务成本仅为PSTN的【五分之一】。开发周期为PSTN的【十分之一】。占地是传统电路交换机的十分之一。,.,CS：MGC媒体网关控制器的功能,ContainsallcallcontrolintelligenceImplementscalllevelfeatures(forward,transfer,conference,hold,),.,Master/slavecontrolofMGsbyMGCsConnectioncontrolDevicecontrolandconfiguration软交换机【MGC】控制各种网关协议：Megaco协议（当前使用）MGCP协议（过去使用）,CS：MGC媒体网关控制器协议,.,CS:软交换系统组成与功能,MegacoProtocol,.,H.248,IP(orATM)Network,PBX/CO,PBX/CO,MediaGateway,Devicecontrol,Devicecontrol,IPPhoneMediaGateway,Telephone/ResidentialMediaGateway,PSTNtrunkingMediaGateway,PSTNlineMediaGateway,PBXMediaGateway,MediaGateway【媒体网关】:功能与分类,ConnectionanddevicecontrolNocallprocessing,nocallmodelService-independent,.,CS:SignalingGateway【信令网关】：功能,SignalingGatewaysprovideinteractionbetweentheSS7networkandMediaGatewayControllers.ConvertSS7toIPpacketsConvertIPtoSS7packetsSignalingtransport(SS7,SIP-T,Q.931)ExtremelysecureExtremelyfaulttolerant,.,MediaGWController,TrunkGateway,Megaco/H.248,VirtualSwitch,Sigtrans,SIP,H.323,PBX,D-channel,B-channels,PRI,VirtualSwitch,RTP,Sigtrans,SignalingGateway,SignalingGateway,SS7,CO,Sigtrans,Sigtrans,TheInternet,SS7Network,CS:SignalingGateway【信令网关】-2,.,Softswitch:MGC之间中继信令,SIPSessionInitialProtocol在Softswitch网络，我们需要一个中继信令取代SS7SIP信令是最佳选择,.,SS7Architecture【专用网络：无法共享】,.,SS7：ISUPCallEstablishment/Release,.,SIPProtocol【基于IP网络文本信令】,SIP,AudioCodecG.711G.723G.729,VideoCodecH.261H.263,RTP,RTCP,LANInterface,TCP,IP,UDP,.,SIPArchitecture,AsignalingprotocolThesetup,modification,andtear-downofmultimediasessionsSIP+SDPDescribethesessioncharacteristicstopotentialsessionparticipantsSeparatesignalingandmediastreamsSignalingmaypassviaoneormoreproxyorredirectserversMediastreamtakesamoredirectpath.,.,SIPCa