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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 Chenhouwu 电话：18911815895,.,Communication Networks 【通信网络的分类】,Communication Network,Switched Communication Network,Virtual Circuit Network: MPLS,Broadcast Communication Network 广播，电视，卫星,Packet Switch (PS) - 分组交换,Datagram Netwo
2、rk: Internet: IP因特网,Circuit-Switched (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 nodes Node to node links usually multiplexed
3、【复用】 Network is usually partially connected Some redundant connections 【冗余连接 】are desirable for reliability Two different switching technologies Circuit 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 tw
4、o stations 【专用/独享的通信通道】 Three phases 【呼叫建立：3个阶段】 Establish Transfer Disconnect Must have switching capacity and channel capacity to establish connection Must have intelligence to work out routing 必须具有智能以对呼叫进行选路,.,Circuit Switching - Applications,Inefficient Channel capacity dedicated for duration of
5、 connection If no data, capacity wasted Set up (connection) takes time Once connected, transfer is transparent Developed for voice traffic (phone: 电话网),.,CS：PSTN 网络结构,PSTN Public Switched Telephone Network Uses digital trunks between Central Office switches (CO) Uses analog line from phones to CO,Di
6、gital Trunks 数字中继,Analog line,Central Office,Central Office,.,PSTN: Public 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 network Few km up to few tens of km Exchange / Swit
7、ch 【交换机】 Switching centers End office - supports subscribers Trunks 【中继线】 Branches between exchanges Multiplexed 【复用】,.,Legacy Digital Circuit Switch,Centralized Intelligence Proprietary Code Proprietary service deployment Very expensive,.,Circuit Switch Elements 【电路交换组成】,.,Circuit Switching Concept
8、s,Digital Switch 【数字交换】 Provide transparent signal path between devices Network Interface 【网络接口】 Control Unit 【控制单元】 Establish connections Generally on demand Handle and acknowledge requests Determine if destination is free construct path Maintain connection Disconnect,.,Node switching System:,.,CS：
9、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 presentation,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-1 Output set: R = 0,1,2,N-1 Defini
10、tion: 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 ; Broadcas
11、t: 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) Output 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, w
12、hich 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 switch,.,Switching Fabric: Space Division,.,Time/Space Division Multiplexing,TIME SWITCH,TIME SWITCH,TIME SWITCH,TIME SWITCH,TIME SWITCH,TIME SWITCH,S
13、PACE SWITCH,.,CS：Blocking or Non-blocking,Blocking 【阻塞】 A network is unable to connect stations because all paths are in use A blocking network allows this 【网络允许Blocking】 Used on voice systems Short duration calls Non-blocking 【无阻塞】 Permits all stations to connect (in pairs) at once Used for some da
14、ta 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 points More than one path through network Increased reliability More complex control May 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
15、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 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 to 30,.,MUX MUX MUX MUX MUX,1 2 3 4,1 2 3 4,E1 E1 E1 E1,E2 E2 E2 E2,E5,2.048
