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1、 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 18911815895 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 Sw
2、itched 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 aredesirable
3、forreliabilityTwodifferentswitchingtechnologiesCircuitswitching 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 EstablishTransferDisconnectMusthaveswitchingcapacityandchannelcapacitytoestab
4、lishconnectionMusthaveintelligencetoworkoutrouting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 PSTN PublicSwit
5、chedTelephoneNetworkUsesdigitaltrunksbetweenCentralOfficeswitches 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
6、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 Circui
7、tSwitchingConcepts 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 Cir
8、tuitSwitch 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 1 Outputset R 0 1 2 N 1 Definition t Tandr Rt Rt R then c t Rt isaconnection tisstartpointoftheconnecti
9、on r Rtistheendpoint ifr Rt Rtcontainsonlyoneitem thisconnectionispointtopoint ifr Rt Rtcontainsmorethanoneitem thisconnectionispointtomulti point Multicast Rt R 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 x
10、1 x0 x2 000 000 001 010 010 100 111 111 SwitchingFabric TimeDivision Time slotswitchingisadevice whichbuffersmincomingtime slots arrangesnewtransmitorderandtransmitsntime slotsUsedinPacketswitchandATMaswellasdigitaltelephoneswitch SwitchingFabric SpaceDivision Time SpaceDivisionMultiplexing TIMESWIT
11、CH 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 atonceU
12、sedforsomedataconnections 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 TimeswitchandSpaceswitc
13、h 1 T接线器 Auserinfo Occupyatimeslot8bitscode 3 TST接线器 512x512TimeSlots CS 电路交换 PSTN TrunkMultiplexing CO1 CO2 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 3 14 15 16 17 30 31 0 1frame 256bits 125ms FrameAlignmen
14、tWord 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
15、 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 6 20 23 1frame 193bits 24c
16、hannels 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 StatisticalTDMFram
