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1、现代通信网络Modern Telecommunication Network,Lecture 3(CS)电路交换与软交换北邮软件学院：陈候武C电话：,Communication Networks 【通信网络的分类】,Communication Network,SwitchedCommunication Network,Virtual Circuit Network: MPLS,BroadcastCommunication Network 广播，电视，卫星,Packet Switch(PS) - 分组交换,Datagram Network: Internet: IP因特网,Circuit-Swi
2、tched(CS) - 电话,通信业务网(Service Network)：分类：,Switched Network：【通信交换网络】,Node Switching （节点交换 ）,A node (switch) in a circuit switching network,Nodes 【交换节点】,Nodes may connect to other nodes only, or to stations and other nodesNode to node links usually multiplexed 【复用】Network is usually partially connecte
3、dSome redundant connections 【冗余连接 】are desirable for reliabilityTwo different switching technologiesCircuit switching 【电路交换】Packet switching 【分组交换】,CS:Circuit Switch电路交换 【Overview】,CS: Circuit Switching 【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：3个阶段】Esta
4、blishTransferDisconnectMust have switching capacity and channel capacity to establish connectionMust have intelligence to work out routing必须具有智能以对呼叫进行选路,Circuit Switching - Applications,InefficientChannel capacity dedicated for duration of connectionIf no data, capacity wastedSet up (connection) tak
5、es timeOnce connected, transfer is transparentDeveloped for voice traffic (phone: 电话网),CS：PSTN 网络结构,PSTN Public Switched Telephone NetworkUses digital trunks between Central Office switches (CO)Uses analog line from phones to CO,Digital Trunks数字中继,Analog line,CentralOffice,CentralOffice,PSTN: Public
6、 Circuit Switched Network,CS: Components 【网络组成】,Subscriber 【用户：电话】Devices attached to network Subscriber line 【用户连线】Local Loop 【本地环路】Subscriber loop 【用户环路】Connection to networkFew km up to few tens of kmExchange / Switch 【交换机】Switching centersEnd office - supports subscribersTrunks 【中继线】Branches bet
7、ween exchangesMultiplexed 【复用】,Legacy Digital Circuit Switch,Centralized IntelligenceProprietary CodeProprietary service deploymentVery expensive,Circuit Switch Elements 【电路交换组成】,Circuit Switching Concepts,Digital Switch 【数字交换】Provide transparent signal path between devicesNetwork Interface 【网络接口】Co
8、ntrol Unit 【控制单元】Establish connectionsGenerally on demandHandle and acknowledge requestsDetermine if destination is freeconstruct pathMaintain connectionDisconnect,Node switching System:,CS：SPC: 电话数字程控交换机 模块,CS:Cirtuit Switch 【Switch Fabric：交换矩阵 】,Switch Fabric: M x N,Switch Fabric: Math graph prese
9、ntation,A input may setup one connection (1,3,6,7), multiple connections (4), or no connection (2,5,8).,Switch Fabric: 数学模型,Input set: T = 0,1,2, M-1Output set: R = 0,1,2,N-1Definition: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
10、. 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 ; Broadcast: Rt = R connection set in switch fabric: C = | c0, c1, c2, |,Switch Fabric: 连接函数,连接函数: input link: x (0 = x = M-1) Outp
11、ut link f(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,Switching Fabric: Time Division,Time-slot switching is a device, which buffers m incoming time-slots, arranges new transmit order and transmits n time-slotsUsed in Packet switch and ATM as we
12、ll as digital telephone switch,Switching Fabric: Space Division,Time/Space Division Multiplexing,TIME SWITCH,TIME SWITCH,TIME SWITCH,TIME SWITCH,TIME SWITCH,TIME SWITCH,SPACE SWITCH,CS：Blocking or Non-blocking,Blocking 【阻塞】A network is unable to connect stations because all paths are in useA blockin
13、g network allows this 【网络允许Blocking】Used on voice systemsShort duration callsNon-blocking 【无阻塞】Permits all stations to connect (in pairs) at onceUsed for some data connections,Switching Fabric: Blocking,如果： I0 正在连续到 O0, 问： I1 可以连接到 O0 or O1 ? 结果：内部阻塞,解决方案：Multistage Switch,Reduced number of cross po
14、intsMore than one path through network Increased reliabilityMore complex controlMay be blocking,解决方案：两级交换矩阵,解决方案：Three Stage Switch,x,x,x,x,CS：TST交换矩阵 - 实例：,TST - Time switch and Space switch(1) T 接线器: A user info. Occupy a time slot 8 bits code.,（3）TST 接线器 512 x 512 Time Slots,CS:电路交换 【PSTN: Trunk
15、Multiplexing】,CO1 CO2: Truck Multiplexing,Mux,.,.,.,.,.,1,1,1,1,1,2,2,2,.,64kb/s voice channel,t4 t3 t2 t1,2Mb/s output signal,同步时分复用：Synchronous TDM,E1: 2Mb/s frame structure,0,1,2,314,15,16,1730,31,0,1 frame - 256 bits - 125ms,Frame Alignment Word,3.9us,Network Signaling,Channels 1 to 15,Channels
16、16 to 30,MUX MUX MUX MUX MUX,12 3 4,1234,E1 E1 E1 E1,E2E2E2E2,E5,2.048 8.448 34.368 139.264 561.480Mbps Mbps Mbps Mbps Mbps,CH2,CH1,CH32,E3 1,E3 2,E3 3,E3 4,E4 1 E4 2 E4 3 E4 4,ITU-T E1 DIGITAL MULTIPLEXING HIERARCHY,E1 E2 E3 E4 E5,ANSI：T1 - T-carrier system 1.544M,Each frame carries one sample (8 b
17、its) for each 24 channels, plus one framing bit = 193 bits193 * 8000 (samples/sec) = 1.544 Mbit/sec = T-1,Channel 1,Channel 2,Channel 3,Channel 24,Channel1,Channel2,Channel3,Channel24,Framing Bit,1 D4 Frame,TDM,ANSI: T1/DS1 Frame Structure - 1.544 Mbps,Every 8th bit used for signalinginefficient,0,1
18、,2,21,22,620,23,1 frame - 193 bits - 24 channels,Bit 8 - reserved for signaling,Framing bit,3,4,5,0,1,Bits 1-7 Payload,ANSI: DIGITAL MULTIPLEXING HIERARCHY,T1 T2 T3 T4 T5,MUX MUX MUX MUX MUX,12 T3 13 T3 24 T3 35 T3 46 T3 57 T3 6,1234,12,T1 T1 T1 T1,T2T2T2T2T2T2T2,T4 T4,T5,CH1 CH2 CH24,24,VF,1.544 6.
19、312 44.736 274.176 560.160 Mbps Mbps Mbps Mbps Mbps,Statistical TDM 【统计时分复用】,In Synchronous TDM many slots are wastedStatistical TDM allocates time slots dynamically based on demandMultiplexer scans input lines and collects data until frame fullData rate on line lower than aggregate rates of input l
20、ines,Statistical TDM Frame Formats,Statistical TDM v Synchronous TDM,Statistics TDM divides a data link into some logic sub-channel,Statistical TDM v Synchronous TDM：Formats,Statistical TDM 举例：HDLC,HDLC： High Level Data Link ControlSynchronous transmissionAll transmissions in framesSingle frame form
21、at for all data and control exchanges,HDLC：Frame Structure,Flag,Address,Control,Information,FCS,Flag,8bits,8extendable,8/16,variable,8,16 / 32,trailer,Frame CheckSum,HDLC：Address Field,Identifies secondary station that sent or will receive frameUsually 8 bits longMay be extended to multiples of 7 bi
22、tsLSB of each octet indicates that it is the last octet (1) or not (0)All ones (11111111) is broadcast,CS:电路交换 【PSTN: Signaling 信令】与【Call Control：呼叫控制】,CS: PSTN 控制信令与呼叫控制 各阶段,Each conversation requires a channel switched throughout the network呼叫请求：Call request；呼叫建立：Call established; 呼叫接收,1. Call is
23、requested,3. Channel is established,2. Call is accepted,PSTN,CS: PSTN 电话号码编码方案,3 digits area code 【区域码】+ 3 digits office code 【局码】 + 4 digits phone 【本局随机码】Each Local Exchange Carrier switch (LEC：本地交换局) are assigned a block of at least 10,000 numbersThe Inter-Exchange Carrier (IXC：汇接局) switches are r
24、esponsible for transmitting long distance,IXC212,LEC555,4210,(212) 555 4210,CS: PSTN Call Routing - 1,International Numbering Plan E.164 【国际电话号码方案】use prefix-based dialing,408,5644,555,PSTN,SS7,CS: PSTN Call Routing - 2,The first LEC 【本地交换机】receives a call, seeing 1 as the first digit and then passe
25、s the call on to the IXC switch. The IXC then routes the call, via SS7, to the remote IXC responsible for 212. 【远端的212中继局】The 212 IXC looks at the office code and passes it on to the 555 LEC switch. 【515本地局】The 555 LEC switch then checks the station code and signals the appropriate phone,Signaling:
26、Control Functions 【控制功能】,Audible communication with subscriberTransmission of dialed numberCall can not be completed indicationCall ended indicationSignal to ring phoneBilling infoEquipment and trunk status infoDiagnostic infoControl of specialist equipment,PSTN：用户信令,Uses loop-start signaling 【环路信令】
27、Indicates if the phone is on-hook or off-hook, or generates ring-tone on phone. Closes circuit when phone is off-hookUses two wires, tip and ring,Tip,FXS,Ring,Switch to Switch Signaling：【中继信令】,Subscribers connected to different switchesOriginating switch seizes interswitch trunkSend off hook signal
28、on trunk, requesting digit register at target switch (for address)Terminating switch sends off hook followed by on hook (wink) to show register readyOriginating switch sends address,中继信令：基本呼叫流程：,中继信令：呼叫控制：FSM Finite State Machine (有限状态机 主叫方 ),PSTN: Signaling Methods【中继信令分类】,CAS Channel Associated Si
29、gnaling 【随路信令】Signaling associated with each channel has fixed placement within frameTraditional T-1 and E-1 for voice uses CASCCS Common Channel Signaling 【共路信令】Signaling passed via messaging protocol, out-of-band signalingCan carry a wide variety of messages, e.g. Caller-ID etcISDN uses a CCS-base
30、d protocol Q.931Q.SIG which is typically used for PBX-to-PBX connectivity, and is a variant of Q.931, is CCD-basedSS7 is the CCS-based protocol used in the PSTN, i.e. between COs,Drawbacks 【缺点】of In CAS,Limited transfer rateDelay between entering address (dialing) and connectionOvercome by use of co
31、mmon channel signaling,CAS v. CCS,SS7：Signaling System Number 7,SS7：Common channel signaling schemeISDNOptimized for 64k digital channel networkCall control, remote control, management and maintenanceReliable means of transfer of info in sequenceWill operate over analog and below 64kPoint to point t
32、errestrial and satellite links,PSTN SS7 /Signaling System 7,SS7 messages are exchanged between network elements on bi-directional channels (typically T1 lines) called signaling links.,Trunk Lines,SSP(CO),SSP(CO),STP,SS7,STP,T-1,T-1,PSTN SS7 Signaling Points,SS7 network is critical to call processing
33、, 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. Links between signaling points are also provisioned in pairs. Traffic is shared across all links in the linkset. If one of the links fa
34、ils, the signaling traffic is rerouted over another link in the linkset.,SS7 Links,STP,STP,SSP,SSP,SCP,SCP,SS7 Links,Trunk Links,SS7：网元功能,SSP (Service Switching Point) SSPs are switches that originate, terminate, or tandem calls. An SSP sends signaling messages to other SSPs to setup, manage, and re
35、lease voice circuits required to complete a call. An SSP may also send a query message to a SCP to determine how to route a call. 【智能网功能】The functionality of the SSP is usually integrated into the CO (Central Office switch：终端局).STP (Signal Transfer Point) 【信号转接点】Network traffic between signaling poi
36、nts may be routed via a packet switch called an STP. An 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 networks.SCP (Service Control Point) 【信号控制点】
37、An SCP is a centralized database that tells an SSP how to route a call (e.g., a toll-free 1-800/888 call ). It 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 【PSTN: 电话网组网原理】,CS：AT&T Telephony Hierarchy,Cl
38、ass 5,Class 4,Class 3,Class 2,Class 1,CS：Telephone Network Model,CS：传统电话网分层结构的问题：,层次太多汇接层次（转接交换机）过多导致呼叫建立延迟传输损失。降低了呼叫接通率降低了系统的可靠性一个转接交换机出问题，将阻塞整个网络网络管理复杂,我国电话网：Two levels of transit network,长途网络结构正在从 4 层演进到 2 层（扁平化）DC1 (direct connection 1) 高层（省间层）DC2 (direct connection 2) 低层（省内层）,CS：局间中继联系方式,DC1 省际
39、：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,All local switches are connected each other by direct trucks. Suitable to less local switches in the same area.,CS: 电话网的路由选择,高效直达路由(H): 永远是首选低呼损直达路由(L): 最后选择用户A 呼叫 用户B：A1-B1, A1-B2-B1, A1-A2-B2-B1, A1-A2-B3-B2-B1, A1-A2-A3-B3-B2-B1,CS：Routi
40、ng 【电路交换：路由定义】,Many connections will need paths through more than one switchNeed to find a routeEfficiencyResilience 【弹性】Public telephone switches are a tree structureStatic routing uses the same approach all the time 【静态路由】Dynamic routing allows for changes in routing depending on traffic 【动态路由】Use
41、s a peer structure for nodes,CS：Alternate Routing 【迂回路由】,Possible routes between end offices predefinedOriginating switch selects appropriate routeRoutes listed in preference orderDifferent sets of routes may be used at different times,CS：Alternate Routing Diagram,CS:电路交换 【SoftSwitch:软交换】,CS 存在问题：解决
42、方案Softswitch,Soft-switch： 优点,General purpose: computer running software to make it a smart phone switchLower costsGreater functionalityPacketizing of digitized voice dataAllowing voice over IPMost complex part of telephone network switch is 【software controlling call process】Call routingCall process
43、ing logicTypically running on proprietary processorSeparate call processing from hardware function of switchPhysical switching done by media gatewayCall processing done by media gateway controller 【softswitch】,Traditional Circuit Switching,CS：Softswitch 【软交换结构】,Media Gateway Controller【媒体网关控制器】 = So
44、ftswitch ：软交换,CS：软交换系统与传统设备区别,核心变化,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。部件间的协议接口基于相应的标准,有利于实现各种异构网的互通。,CS：传统PSTN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 Arch,SS7SignallingGateway,PSTNTrunks,MediaGatew
45、ay(Trunking),PSTNOriginating orTandemSwitch(es),SS7Network,MediaGatewayController,MediaGateway(Trunking),RTP/UDP/IP Stream,Megaco,SS7SignallingGateway,Megaco,MediaGatewayController,PSTNTrunks,VoIP Terminals,PSTNOriginating orTandemSwitch(es),SS7Network,M3UA/SCTP,SS7,SS7,TDM,TDM,M3UA/SCTP,SIP-T,CS：软交
46、换结构 网元组成,Media Gateway Controller（MGC）：Softswitch:Signaling Gateway 【信令网关】Media Gateway 【媒体网关】 Trunking gateway Line Gateway Residential Gateway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,Contains all call control intelligenceImplements call level features (forward, tr
47、ansfer, conference, hold, ),Master / slave control of MGs by MGCs Connection control Device control and configuration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,Megaco Protocol,H.248,IP (or ATM) Network,PBX/CO,PBX/CO,Media Gateway,Devicecontrol,Devicecontrol,IP
48、 PhoneMedia Gateway,Telephone/ResidentialMedia Gateway,PSTN trunkingMedia Gateway,PSTN lineMedia Gateway,PBXMedia Gateway,Media Gateway【媒体网关】: 功能与分类,Connection and device controlNo call processing, no call modelService-independent,CS: Signaling Gateway【信令网关】：功能,Signaling Gateways provide interaction
49、 between the SS7 network and Media Gateway Controllers.Convert SS7 to IP packetsConvert IP to SS7 packetsSignaling transport (SS7, SIP-T, Q.931)Extremely secureExtremely fault tolerant,Media GW Controller,Trunk Gateway,Megaco/H.248,Virtual Switch,Sigtrans,SIP, H.323,PBX,D-channel,B-channels,PRI,Virt
50、ual Switch,RTP,Sigtrans,Signaling Gateway,Signaling Gateway,SS7,CO,Sigtrans,Sigtrans,TheInternet,SS7Network,CS: Signaling Gateway【信令网关】- 2,Softswitch: MGC 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SS7SIP 信令是最佳选择,SS7 Architecture 【专用网络：无法共享】,SS7：ISUP Call Establishment/Release,SIP
