现代通信网络课件3

1、现代通信网络现代通信网络Modern Telecommunication NetworkLecture 3(CS)电路交换与软交换电路交换与软交换北邮软件学院：陈候武北邮软件学院：陈候武C电话：电话ommunication Networks 【通信网络的分类通信网络的分类】Communication NetworkSwitchedCommunication NetworkVirtual Circuit Network: MPLSBroadcastCommunication Network 广播，电视，卫星广播，电视，卫星Packet Switch(PS) - 分组交换

2、分组交换Datagram Network: Internet: IP因特网因特网Circuit-Switched(CS) - 电话电话通信业务网通信业务网(Service Network)(Service Network)：分类：分类：Switched Network：【通信交换网络通信交换网络】Node Switching （节点交换节点交换 ） A node (switch) in a circuit switching networkincoming linksoutgoing linksNodeNodes 【交换节点交换节点】 Nodes may connect to other no

3、des only, or to stations and other nodes Node to node links usually multiplexed 【复用】 Network is usually partially connectedpSome redundant connections 【冗余连接冗余连接 】are desirable for reliability Two different switching technologiespCircuit switching 【电路交换电路交换】pPacket switching 【分组交换分组交换】CS:Circuit Swit

4、ch电路交换电路交换 【Overview】CS: Circuit Switching 【电路交换电路交换】 Dedicated communication path between two stations 【专用/独享的通信通道】 Three phases 【呼叫建立：呼叫建立：3个阶段个阶段】pEstablishpTransferpDisconnect Must have switching capacity and channel capacity to establish connection Must have intelligence to work out routingp必须必

5、须具有智能以对呼叫进行选路具有智能以对呼叫进行选路Circuit Switching - Applications InefficientpChannel capacity dedicated for duration of connectionpIf no data, capacity wasted Set up (connection) takes time Once connected, transfer is transparent Developed for voice traffic (phone: 电话网电话网)CS：PSTN 网络结构网络结构lPSTN Public Switc

6、hed Telephone NetworklUses digital trunks between Central Office switches (CO)lUses analog line from phones to CODigital Trunks数字中继数字中继Analog lineCentralOfficeCentralOfficePSTN: Public Circuit Switched NetworkCS: Components 【网络组成】 Subscriber 【用户：电话】pDevices attached to network Subscriber line 【用户连线用

7、户连线】pLocal Loop 【本地环路本地环路】pSubscriber loop 【用户环路用户环路】pConnection to networkpFew km up to few tens of km Exchange / Switch 【交换机交换机】pSwitching centerspEnd office - supports subscribers Trunks 【中继线中继线】pBranches between exchangespMultiplexed 【复用复用】Legacy Digital Circuit SwitchlCentralized IntelligencelP

8、roprietary CodelProprietary service deploymentlVery expensiveTrunkCardTrunkCardTrunkCardLineCardLineCardLineCardSwitch ControllerNext SwitchNext SwitchNext SwitchSS7 NetworkCircuit Switch Elements 【电路交换组成】Circuit Switching Concepts Digital Switch 【数字交换数字交换】pProvide transparent signal path between de

9、vices Network Interface 【网络接口网络接口】 Control Unit 【控制单元控制单元】pEstablish connections Generally on demand Handle and acknowledge requests Determine if destination is free construct pathpMaintain connectionpDisconnectNode switching System:Node switching System:CSCS：SPC: SPC: 电话数字程控交换机电话数字程控交换机 模块模块CS:Cirt

10、uit Switch 【Switch Fabric：交换矩阵：交换矩阵 】Switch Fabric: M x NSwitch Fabric: Math graph presentationSwitch Fabric: Math graph presentationA input may setup one connection (1,3,6,7), multiple connections (4), or no connection (2,5,8).Switch Fabric: 数学模型数学模型 Input set: T = 0,1,2, M-1 Output set: R = 0,1,2,

11、N-1 Definition: t T and r Rt， Rt R ， then: c = | t, Rt | is a connection. t is start point of the connection, r Rt is the end point. if r Rt, Rt contains only one item,this connection is point to point. if r Rt, Rt contains more than one item,this connection is point to multi-point. Multicast: Rt R

12、; Broadcast: Rt = R connection set in switch fabric: C = | c0, c1, c2, |Switch Fabric: Switch Fabric: 连接函数连接函数连接函数连接函数: input link: x (0 = x = M-1) Output link f(x) (0 = f(x) = N-1). 例如：连接函数例如：连接函数: (x2, x1, x0) = x1, x0, x2 (000)=000, (001)=010, (010)=100, (111)=111Switching Fabric: Time DivisionSw

13、itching Fabric: Time Division Time-slot switching is a device, which buffers m incoming time-slots, arranges new transmit order and transmits n time-slots Used in Packet switch and ATM as well as digital telephone switchSwitching Fabric: Space DivisionSwitching Fabric: Space DivisionTime/Space Divis

14、ion Multiplexing TIME SWITCHTIME SWITCHTIME SWITCHTIME SWITCHTIME SWITCHTIME SWITCHSPACE SWITCHCS：Blocking or Non-blocking Blocking 【阻塞】pA network is unable to connect stations because all paths are in usepA blocking network allows this 【网络允许Blocking】pUsed on voice systems Short duration calls Non-b

15、locking 【无阻塞】pPermits all stations to connect (in pairs) at oncepUsed for some data connectionsSwitching Fabric: BlockingSwitching Fabric: Blocking解决解决方案：方案：Multistage SwitchlReduced number of cross pointslMore than one path through networkp Increased reliabilitylMore complex controllMay be blocking

16、解决解决方案：两级交换矩阵方案：两级交换矩阵解决方案解决方案：Three Stage Switchx xx xx xx xCS：TST交换矩阵交换矩阵 - - 实例：实例：TST - Time switch and Space switch(1) T 接线器: A user info. Occupy a time slot 8 bits code.（3 3）TST TST 接线器接线器 512 x 512 Time Slots512 x 512 Time SlotsCS:电路交换电路交换 【PSTN: Trunk Multiplexing】CO1 CO2: Truck Multiplexing

17、Mux.11111222.64kb/s voice channelt4 t3 t2 t12Mb/s output signal同步时分复用：同步时分复用：Synchronous TDMSynchronous TDME1: 2Mb/s frame structureAll Timeslots contain 8 bit words(PCM, Data, Subrate, n x 64 kb/s)Network Signaling - CAS or CCS01231415 1617303101 frame - 256 bits - 125msFrame Alignment Word3.9usNet

18、work SignalingChannels 1 to 15Channels 16 to 30 MUX MUX MUX MUX MUX12 3 4 1234 E1 E1 E1 E1E2E2E2E2 E52.048 8.448 34.368 139.264 561.480Mbps Mbps Mbps Mbps Mbps CH2 CH1 CH32E3 1E3 2E3 3E3 4 E4 1 E4 2 E4 3 E4 4 ITU-T E1 DIGITAL MULTIPLEXING HIERARCHYE1 E2 E3 E4 E5ANSI：T1 - T-carrier system 1.544MlEach

19、 frame carries one sample (8 bits) for each 24 channels, plus one framing bit = 193 bitsl193 * 8000 (samples/sec) = 1.544 Mbit/sec = T-1Channel 1Channel 2Channel 3Channel 24Channel1Channel2Channel3Channel24Framing Bit1 D4 FrameTDM ANSI: T1/DS1 Frame Structure - 1.544 Mbps Every 8th bit used for sign

20、alingpinefficient01221 22620231 frame - 193 bits - 24 channelsBit 8 - reserved for signalingFraming bit34501Bits 1-7 PayloadANSI: DIGITAL MULTIPLEXING HIERARCHYT1 T2 T3 T4 T5 MUX MUX MUX MUX MUX12 T3 13 T3 24 T3 35 T3 46 T3 57 T3 6123412 T1 T1 T1 T1T2T2T2T2T2T2T2 T4 T4T5 CH1 CH2 CH2424VF1.544 6.312

21、44.736 274.176 560.160 Mbps Mbps Mbps Mbps Mbps Statistical TDM 【统计时分复用统计时分复用】 In Synchronous TDM many slots are wasted Statistical TDM allocates time slots dynamically based on demand Multiplexer scans input lines and collects data until frame full Data rate on line lower than aggregate rates of in

22、put linesStatistical TDM Frame FormatsStatistical TDM v Synchronous TDMSynchronous TDM Statistics TDM divides a data link into some logic sub-channelStatistical TDM v Synchronous TDM：FormatsStatistical TDM 举例：举例：HDLCHDLC HDLC： High Level Data Link Control Synchronous transmission All transmissions i

23、n frames Single frame format for all data and control exchangesHDLC：Frame Structure FlagAddress ControlInformationFCSFlag8bits8extendable8/16variable816 / 32trailerFrame CheckSumHDLC：Address Field Identifies secondary station that sent or will receive frame Usually 8 bits long May be extended to mul

24、tiples of 7 bitspLSB of each octet indicates that it is the last octet (1) or not (0) All ones (11111111) is broadcastCS:电路交换电路交换 【PSTN: Signaling 信令信令】与与【Call Control：呼叫控制：呼叫控制】CS: PSTN 控制信令与呼叫控制控制信令与呼叫控制 各阶段各阶段lEach conversation requires a channel switched throughout the networkl呼叫请求：呼叫请求：Call req

25、uest；呼叫建立：；呼叫建立：Call established; 呼叫接收呼叫接收1. Call is requested3. Channel is established2. Call is acceptedPSTNCS: PSTN 电话号码编码方案电话号码编码方案l3 digits area code 【区域码区域码】+ 3 digits office code 【局码局码】 + 4 digits phone 【本局随机码本局随机码】lEach Local Exchange Carrier switch (LEC：本地交换局：本地交换局) are assigned a block of

26、at least 10,000 numberslThe Inter-Exchange Carrier (IXC：汇接局：汇接局) switches are responsible for transmitting long distanceIXC212LEC5554210(212) 555 4210CS: PSTN Call Routing - 1lInternational Numbering Plan E.164 【国际电话号码方案国际电话号码方案】luse prefix-based dialing4085644555212PSTN1+212+555+5644SS7CS: PSTN Cal

27、l Routing - 2lThe first LEC 【本地交换机本地交换机】receives a call, seeing 1 as the first digit and then passes the call on to the IXC switch. lThe IXC then routes the call, via SS7, to the remote IXC responsible for 212. 【远端的212中继局】lThe 212 IXC looks at the office code and passes it on to the 555 LEC switch.

28、【515本地局】lThe 555 LEC switch then checks the station code and signals the appropriate phoneSignaling: Control Functions 【控制功能】lAudible communication with subscriberlTransmission of dialed numberlCall can not be completed indicationlCall ended indicationlSignal to ring phonelBilling infolEquipment and

29、 trunk status infolDiagnostic infolControl of specialist equipmentPSTN：用户信令用户信令lUses loop-start signaling 【环路信令】pIndicates if the phone is on-hook or off-hook, or generates ring-tone on phone. pCloses circuit when phone is off-hooklUses two wires, tip and ringTipFXSRingSwitch to Switch Signaling：【中继

30、信令中继信令】 Subscribers connected to different switches Originating switch seizes interswitch trunk Send off hook signal on trunk, requesting digit register at target switch (for address) Terminating switch sends off hook followed by on hook (wink) to show register ready Originating switch sends address

31、中继信令：基本呼叫流程：中继信令：基本呼叫流程：中继信令：中继信令：呼叫控制呼叫控制：FSM Finite State Machine (有限状态机有限状态机 主叫方主叫方 )挂机状态挂机状态摘机状态摘机状态通话状态通话状态拨号状态拨号状态忙音状态忙音状态振铃状态振铃状态请求呼叫状态请求呼叫状态回铃状态回铃状态摘机摘机拨号拨号拨号正确拨号正确拨号拨号拨号错误拨号错误被叫振铃被叫振铃被叫摘机被叫摘机被叫用户忙被叫用户忙被叫无应答被叫无应答被叫挂机被叫挂机主叫挂机主叫挂机收到新的呼叫收到新的呼叫摘机摘机 PSTN: Signaling Methods【中继信令分类中继信令分类】lCAS Chann

32、el Associated Signaling 【随路信令】pSignaling associated with each channel has fixed placement within framepTraditional T-1 and E-1 for voice uses CASlCCS Common Channel Signaling 【共路信令】pSignaling passed via messaging protocol, out-of-band signalingpCan carry a wide variety of messages, e.g. Caller-ID et

33、cpISDN uses a CCS-based protocol Q.931pQ.SIG which is typically used for PBX-to-PBX connectivity, and is a variant of Q.931, is CCD-basedpSS7 is the CCS-based protocol used in the PSTN, i.e. between COsDrawbacks 【缺点缺点】of In CASlLimited transfer ratelDelay between entering address (dialing) and conne

34、ctionlOvercome by use of common channel signalingCAS v. CCSSS7：Signaling System Number 7 SS7：Common channel signaling scheme ISDN Optimized for 64k digital channel network Call control, remote control, management and maintenance Reliable means of transfer of info in sequence Will operate over analog

35、 and below 64k Point to point terrestrial and satellite linksPSTN SS7 /Signaling System 7SS7 messages are exchanged between network elements on bi-directional channels (typically T1 lines) called signaling links. Trunk LinesSSP(CO)SSP(CO)STPSS7STPT-1T-1PSTN SS7 Signaling Points l SS7 network is crit

36、ical to call processing, SCPs and STPs are usually deployed in mated pair configurations in separate physical locations to ensure network-wide service in the event of an isolated failure. lLinks between signaling points are also provisioned in pairs. Traffic is shared across all links in the linkset

37、. If one of the links fails, the signaling traffic is rerouted over another link in the linkset. SS7 LinksSTPSTPSSPSSPSCPSCPSS7 LinksTrunk LinksSS7：网元功能：网元功能lSSP (Service Switching Point) pSSPs are switches that originate, terminate, or tandem calls. pAn SSP sends signaling messages to other SSPs to

38、 setup, manage, and release voice circuits required to complete a call.p An SSP may also send a query message to a SCP to determine how to route a call. 【智能网功能智能网功能】pThe functionality of the SSP is usually integrated into the CO (Central Office switch：终端局：终端局).lSTP (Signal Transfer Point) 【信号转接点信号转接

39、点】pNetwork traffic between signaling points may be routed via a packet switch called an STP. pAn STP routes each incoming message to an outgoing signaling link based on routing information contained in the SS7 message. An STP can also act as a firewall to screen SS7 messages exchanged with other net

40、works.lSCP (Service Control Point) 【信号控制点信号控制点】pAn SCP is a centralized database that tells an SSP how to route a call (e.g., a toll-free 1-800/888 call ). pIt sends a response to the originating SSP containing the routing number(s) associated with the dialed number.SS7：信令功能 SS7 在移动网络中漫游功能的应用CS:电路交换

41、电路交换 【PSTN: 电话网组网原理电话网组网原理】CS：AT&T Telephony Hierarchy110987324561231231236566672282292301298129913001234519,000200 million telephones19,000 endoffices1300 tolloffices230 primaryoffices67 sectionaloffices10 regionaloffices(full mesh)Class 5Class 4Class 3Class 2Class 1CS：Telephone Network ModelRegion

42、al CenterClass 1 switchSectional CenterClass 2 switchPrimary CenterClass 3 switchToll CenterClass 4 switchEnd OfficeClass 5 switchRegional CenterClass 1 switchSectional CenterClass 2 switchPrimary CenterClass 3 switchToll CenterClass 4 switchEnd OfficeClass 5 switchVoiceVoiceTo otherRegional centers

43、Sectional centersPrimary centersToll centersEnd officesTo otherPrimary centersToll centersEnd officesTo otherClass 4 toll pointsEnd officesFigure 1.1 Telephone Network ModelLegend:LoopDirect TrunkToll-Connecting TrunkToll TrunkCSCS：传统电话网分层结构的问题：传统电话网分层结构的问题：l层次太多层次太多p汇接层次（转接交换机）过多导致呼叫建立延迟p传输损失。降低了呼叫

44、接通率l降低了系统的可靠性降低了系统的可靠性p一个转接交换机出问题，将阻塞整个网络l网络管理复杂网络管理复杂我国电话网我国电话网：Two levels of transit network l长途网络结构正在从 4 层演进到 2 层（扁平化）pDC1 (direct connection 1) 高层（省间层）pDC2 (direct connection 2) 低层（省内层）CS：局间中继联系方式局间中继联系方式DC1 省际：互联至其他省；省内：星型连接至DC2DC2 同层DC2之间互联，或者部分互联，也可直连至其他省CS：本地网互联方式本地网互联方式All local switches ar

45、e connected each other by direct trucks. Suitable to less local switches in the same area.CS: 电话网的路由选择电话网的路由选择高效直达路由高效直达路由(H): 永远是首选永远是首选低呼损直达路由低呼损直达路由(L): 最后选择最后选择用户用户A 呼叫呼叫 用户用户B：A1-B1, A1-B2-B1, A1-A2-B2-B1, A1-A2-B3-B2-B1, A1-A2-A3-B3-B2-B1lMany connections will need paths through more than one

46、switchlNeed to find a routepEfficiencypResilience 【弹性弹性】lPublic telephone switches are a tree structurepStatic routing uses the same approach all the time 【静态路由静态路由】lDynamic routing allows for changes in routing depending on traffic 【动态路由动态路由】pUses a peer structure for nodeslPossible routes between

47、end offices predefinedlOriginating switch selects appropriate routelRoutes listed in preference orderlDifferent sets of routes may be used at different timesCS:电路交换电路交换 【SoftSwitch:软交换软交换】CS 存在问题：存在问题：解决方案解决方案Softswitch Soft-switch： 优点General purpose: computer running software to make it a smart pho

48、ne switchLower costsGreater functionalitypPacketizing of digitized voice datapAllowing voice over IPMost complex part of telephone network switch is 【software controlling call process】pCall routingpCall processing logicpTypically running on proprietary processorSeparate call processing from hardware

49、 function of switchPhysical switching done by media gatewayCall processing done by media gateway controller 【softswitch】Traditional Circuit SwitchingCS：Softswitch 【软交换结构】Media Gateway Controller【媒体网关控制器媒体网关控制器】 = Softswitch ：软交换：软交换CS：软交换系统与传统设备区别：软交换系统与传统设备区别 电路交换模型电路交换模型呼叫控制呼叫控制SS7SS7 Line Line Ca

50、rdCardTrunk Trunk CardCardTime Time Slot Slot 交交换换T TD DM MT TD DM M管理系统管理系统计费系统计费系统IPIPATMATM软交换软交换SS7SS7MGMGMGMGIPIPATMATMH.248/MGCPH.248/MGCPH.248/MGCPH.248/MGCP软交换模型软交换模型T TD DM MT TD DM M分组网分组网扩展业务扩展业务管理系统管理系统计费系统计费系统将传统交换机的功能模块分离成为独立的网络部件，各个部件可以按相应的功将传统交换机的功能模块分离成为独立的网络部件，各个部件可以按相应的功能划分各自独立发展。

51、部件间的协议接口基于相应的标准能划分各自独立发展。部件间的协议接口基于相应的标准,有利于实现各种异构有利于实现各种异构网的互通。网的互通。CSCS：传统：传统PSTNPSTN网络存在问题网络存在问题 传统网络的仅支持单业务(语音)交换能力成为发展的最大瓶颈, 低层交换能力支持并约束了高层能力; 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 - IP ArchSS7SignallingGatewayPSTNTrunksMediaGateway(Trunking)PSTNOriginating o

52、rTandemSwitch(es)SS7NetworkMediaGatewayControllerMediaGateway(Trunking)RTP/UDP/IP StreamMegacoSS7SignallingGatewayMegacoMediaGatewayControllerPSTNTrunksVoIP TerminalsPSTNOriginating orTandemSwitch(es)SS7NetworkM3UA/SCTPSS7SS7TDMTDMM3UA/SCTPSIP-TCSCS：软交换结构：软交换结构 网元组成网元组成 Media Gateway Controller（MGC）

53、：Softswitch: Signaling Gateway 【信令网关】 Media Gateway 【媒体网关】p Trunking gatewayp Line Gatewayp Residential Gateway 软交换的新业务成本仅为软交换的新业务成本仅为PSTN的的【五分之一五分之一】。开发周。开发周期为期为PSTN的的【十分之一十分之一】。占地是传统电路交换机的十。占地是传统电路交换机的十分之一。分之一。CS：MGC 媒体网关控制器的功能媒体网关控制器的功能 Contains all call control intelligence Implements call level

54、 features (forward, transfer, conference, hold, )挂机状态挂机状态摘机状态摘机状态通话状态通话状态拨号状态拨号状态忙音状态忙音状态振铃状态振铃状态请求呼叫状态请求呼叫状态回铃状态回铃状态摘机摘机拨号拨号拨号正确拨号正确拨号拨号拨号错误拨号错误被叫振铃被叫振铃被叫摘机被叫摘机被叫用户忙被叫用户忙被叫无应答被叫无应答被叫挂机被叫挂机主叫挂机主叫挂机收到新的呼叫收到新的呼叫摘机摘机 Master / slave control of MGs by MGCsp Connection controlp Device control and configur

55、ation 软交换机软交换机【MGC】控制各种网关协议：控制各种网关协议：p Megaco 协议协议 （当前使用）（当前使用）p MGCP 协议协议 （过去使用）（过去使用）CS：MGC 媒体网关控制器协议媒体网关控制器协议Endpoint(eg. H.323 Gateway, Terminal, MCU) Gateway Function(eg. H.323 Gateway, Terminal, MCU) Call AgentMedia Gateway ControllerSignalling GatewayPSTN,ATM,etctrunkslinesSS7 etcSigtranAnalo

56、gMedia GatewayPSTN trunkingMedia GatewayPSTN lineMedia GatewayIP PhoneMedia GatewayMegaco ScopeCS: 软交换系统组成与功能软交换系统组成与功能 Megaco ProtocolCall control (eg. H.323, SIP)H.248IP (or ATM) NetworkPBX/COPBX/COMedia GW ControllerMedia GatewayDevicecontrolDevicecontrolIP PhoneMedia GatewayTelephone/Residential

57、Media GatewayPSTN trunkingMedia GatewayPSTN lineMedia GatewayPBXMedia GatewayConnection and device controlNo call processing, no call modelService-independentCS: Signaling Gateway【信令网关信令网关】：功能：功能lSignaling Gateways provide interaction between the SS7 network and Media Gateway Controllers.lConvert SS

58、7 to IP packetslConvert IP to SS7 packetslSignaling transport (SS7, SIP-T, Q.931)lExtremely securelExtremely fault tolerantMedia GW ControllerTrunk GatewayMegaco/H.248Virtual SwitchSigtransSIP, H.323Media GatewaySignalling GatewayPBXD-channelB-channelsPRIVirtual SwitchRTPSigtransSignaling GatewaySig

59、naling GatewaySS7COSigtransSigtransCS: Signaling Gateway【信令网关信令网关】- 2- 2Softswitch: MGC 之间中继信令之间中继信令 SIP Session Initial Protocol 在Softswitch 网络，我们需要一个中继信令取代SS7 SIP 信令是最佳选择SS7 Architecture 【专用网络：无法共享专用网络：无法共享】SS7：ISUP Call Establishment/ReleaseSIPAudio CodecG.711G.723G.729Video CodecH.261H.263RTPRTCPLAN InterfaceTCPIPUDPSIP Architecture l A signaling protocolpThe setup, modification, and tear-down of multime