现代通信网络课件

1、现代通信网络Modern Telecommunication Network,Lecture 3 (CS)电路交换与软交换 电话：,1,学习交流PPT,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-S

2、witched (CS) - 电话,2,学习交流PPT,通信业务网(Service Network)：分类：,3,学习交流PPT,Switched Network：【通信交换网络】,4,学习交流PPT,Node Switching （节点交换 ）,A node (switch) in a circuit switching network,5,学习交流PPT,Nodes 【交换节点】,Nodes may connect to other nodes only, or to stations and other nodes Node to node links usually multiplex

3、ed 【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】,6,学习交流PPT,CS:Circuit Switch 电路交换 【Overview】,7,学习交流PPT,CS: Circuit Switching 【电路交换】,Dedicated communicat

4、ion path between two 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,8,学习交流PPT,Circuit Switching - Applications,Inefficient Channel capacit

5、y dedicated for duration of connection If no data, capacity wasted Set up (connection) takes time Once connected, transfer is transparent Developed for voice traffic (phone: 电话网),9,学习交流PPT,CS：PSTN 网络结构,PSTN Public Switched Telephone Network Uses digital trunks between Central Office switches (CO) Us

6、es analog line from phones to CO,Digital Trunks 数字中继,Analog line,Central Office,Central Office,10,学习交流PPT,PSTN: Public Circuit Switched Network,11,学习交流PPT,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 t

7、o network Few km up to few tens of km Exchange / Switch 【交换机】 Switching centers End office - supports subscribers Trunks 【中继线】 Branches between exchanges Multiplexed 【复用】,12,学习交流PPT,Legacy Digital Circuit Switch,Centralized Intelligence Proprietary Code Proprietary service deployment Very expensive,

8、13,学习交流PPT,Circuit Switch Elements 【电路交换组成】,14,学习交流PPT,Circuit Switching Concepts,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 f

9、ree construct path Maintain connection Disconnect,15,学习交流PPT,Node switching System:,16,学习交流PPT,CS：SPC: 电话数字程控交换机 模块,17,学习交流PPT,CS:Cirtuit Switch 【Switch Fabric：交换矩阵 】,18,学习交流PPT,Switch Fabric: M x N,19,学习交流PPT,Switch Fabric: Math graph presentation,A input may setup one connection (1,3,6,7), multipl

10、e connections (4), or no connection (2,5,8).,20,学习交流PPT,Switch Fabric: 数学模型,Input set: T = 0,1,2, M-1 Output set: R = 0,1,2,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 con

11、nection 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, |,21,学习交流PPT,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：

12、连接函数: (x2, x1, x0) = x1, x0, x2 (000)=000, (001)=010, (010)=100, (111)=111,22,学习交流PPT,Switching 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 telephon

13、e switch,23,学习交流PPT,Switching Fabric: Space Division,24,学习交流PPT,Time/Space Division Multiplexing,TIME SWITCH,TIME SWITCH,TIME SWITCH,TIME SWITCH,TIME SWITCH,TIME SWITCH,SPACE SWITCH,25,学习交流PPT,CS：Blocking or Non-blocking,Blocking 【阻塞】 A network is unable to connect stations because all paths are in

14、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 data connections,26,学习交流PPT,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,27,学习交流PPT,解决方案：Mult

15、istage Switch,Reduced number of cross points More than one path through network Increased reliability More complex control May be blocking,28,学习交流PPT,解决方案：两级交换矩阵,29,学习交流PPT,解决方案：Three Stage Switch,x,x,x,x,30,学习交流PPT,CS：TST交换矩阵 - 实例：,TST - Time switch and Space switch (1) T 接线器: A user info. Occupy a

16、 time slot 8 bits code.,31,学习交流PPT,（3）TST 接线器 512 x 512 Time Slots,32,学习交流PPT,CS:电路交换 【PSTN: Trunk Multiplexing】,33,学习交流PPT,CO1 CO2: Truck Multiplexing,34,学习交流PPT,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,35,学习交流PPT,E1: 2Mb/s frame st

17、ructure,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 30,36,学习交流PPT,MUX MUX MUX MUX MUX,1 2 3 4,1 2 3 4,E1 E1 E1 E1,E2 E2 E2 E2,E5,2.048 8.448 34.368 139.264 561.480 Mbps Mbps Mbps Mbps Mbps,CH2,CH1,CH32,E3 1,E3 2,E3

18、 3,E3 4,E4 1 E4 2 E4 3 E4 4,ITU-T E1 DIGITAL MULTIPLEXING HIERARCHY,E1 E2 E3 E4 E5,37,学习交流PPT,ANSI：T1 - T-carrier system 1.544M,Each frame carries one sample (8 bits) for each 24 channels, plus one framing bit = 193 bits 193 * 8000 (samples/sec) = 1.544 Mbit/sec = T-1,Channel 1,Channel 2,Channel 3,C

19、hannel 24,Channel 1,Channel 2,Channel 3,Channel 24,Framing Bit,1 D4 Frame,TDM,38,学习交流PPT,ANSI: T1/DS1 Frame Structure - 1.544 Mbps,Every 8th bit used for signaling inefficient,0,1,2,21,22,620,23,1 frame - 193 bits - 24 channels,Bit 8 - reserved for signaling,Framing bit,3,4,5,0,1,Bits 1-7 Payload,39

20、,学习交流PPT,ANSI: DIGITAL MULTIPLEXING HIERARCHY,T1 T2 T3 T4 T5,MUX MUX MUX MUX MUX,1 2 T3 1 3 T3 2 4 T3 3 5 T3 4 6 T3 5 7 T3 6,1 2 3 4,1 2,T1 T1 T1 T1,T2 T2 T2 T2 T2 T2 T2,T4 T4,T5,CH1 CH2 CH24,24,VF,1.544 6.312 44.736 274.176 560.160 Mbps Mbps Mbps Mbps Mbps,40,学习交流PPT,41,学习交流PPT,Statistical TDM 【统计时

21、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 input lines,42,学习交流PPT,Statistical TDM Frame Formats,43,学习交流PPT,Statistical

22、TDM v Synchronous TDM,Statistics TDM divides a data link into some logic sub-channel,44,学习交流PPT,Statistical TDM v Synchronous TDM：Formats,45,学习交流PPT,Statistical TDM 举例：HDLC,HDLC： High Level Data Link Control Synchronous transmission All transmissions in frames Single frame format for all data and co

23、ntrol exchanges,46,学习交流PPT,HDLC：Frame Structure,Flag,Address,Control,Information,FCS,Flag,8 bits,8 extendable,8/16,variable,8,16 / 32,trailer,Frame CheckSum,47,学习交流PPT,HDLC：Address Field,Identifies secondary station that sent or will receive frame Usually 8 bits long May be extended to multiples of

24、7 bits LSB of each octet indicates that it is the last octet (1) or not (0) All ones (11111111) is broadcast,48,学习交流PPT,CS:电路交换 【PSTN: Signaling 信令】 与 【Call Control：呼叫控制】,49,学习交流PPT,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：Cal

25、l established; 呼叫接收,1. Call is requested,3. Channel is established,2. Call is accepted,50,学习交流PPT,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 numbers The Int

26、er-Exchange Carrier (IXC：汇接局) switches are responsible for transmitting long distance,IXC 212,LEC 555,4210,(212) 555 4210,51,学习交流PPT,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,SS7,52,学习交流PPT,CS: PSTN Call Routing - 2,The first L

27、EC 【本地交换机】receives a call, seeing 1 as the first digit and then passes 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 the

28、n checks the station code and signals the appropriate phone,53,学习交流PPT,Signaling: Control Functions 【控制功能】,Audible communication with subscriber Transmission of dialed number Call can not be completed indication Call ended indication Signal to ring phone Billing info Equipment and trunk status info

29、Diagnostic info Control of specialist equipment,54,学习交流PPT,PSTN：用户信令,Uses loop-start signaling 【环路信令】 Indicates if the phone is on-hook or off-hook, or generates ring-tone on phone. Closes circuit when phone is off-hook Uses two wires, tip and ring,Tip,FXS,Ring,55,学习交流PPT,Switch to Switch Signaling：

30、【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、56,学习交流PPT,中继信令：基本呼叫流程：,57,学习交流PPT,中继信令：呼叫控制：FSM Finite State Machine (有限状态机 主叫方 ),58,学习交流PPT,PSTN: Signaling Methods【中继信令分类】,CAS Channel Associated Signaling 【随路信令】 Signaling associated with each channel has fixed placement within frame Traditional T-1 and E-1 for voice uses CAS CCS Common Channel

32、Signaling 【共路信令】 Signaling passed via messaging protocol, out-of-band signaling Can carry a wide variety of messages, e.g. Caller-ID etc ISDN uses a CCS-based protocol Q.931 Q.SIG which is typically used for PBX-to-PBX connectivity, and is a variant of Q.931, is CCD-based SS7 is the CCS-based protoc

33、ol used in the PSTN, i.e. between COs,59,学习交流PPT,Drawbacks 【缺点】of In CAS,Limited transfer rate Delay between entering address (dialing) and connection Overcome by use of common channel signaling,60,学习交流PPT,CAS v. CCS,61,学习交流PPT,SS7：Signaling System Number 7,SS7：Common channel signaling scheme ISDN O

34、ptimized for 64k digital channel network Call control, remote control, management and maintenance Reliable means of transfer of info in sequence Will operate over analog and below 64k Point to point terrestrial and satellite links,62,学习交流PPT,PSTN SS7 /Signaling System 7,SS7 messages are exchanged be

35、tween network elements on bi-directional channels (typically T1 lines) called signaling links.,Trunk Lines,SSP (CO),SSP (CO),STP,SS7,STP,T-1,T-1,63,学习交流PPT,PSTN SS7 Signaling Points,SS7 network is critical to call processing, SCPs and STPs are usually deployed in mated pair configurations in separat

36、e 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 fails, the signaling traffic is rerouted over another link in the linkset.,SS7

37、 Links,STP,STP,SSP,SSP,SCP,SCP,SS7 Links,Trunk Links,64,学习交流PPT,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 release voice circuits required to complete a call. An SSP may also

38、 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 points may be routed via a packet switch called an STP. An STP ro

39、utes 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】 An SCP is a centralized database that tells an SSP how to ro

40、ute 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.,65,学习交流PPT,SS7：信令功能,SS7 在移动网络中漫游功能的应用,66,学习交流PPT,CS:电路交换 【PSTN: 电话网组网原理】,67,学习交流PPT,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

41、限;,84,学习交流PPT,CS: Softswitch: PSTN - IP Arch,SS7 Signalling Gateway,PSTN Trunks,Media Gateway (Trunking),PSTN Originating or Tandem Switch(es),SS7 Network,Media Gateway Controller,Media Gateway (Trunking),RTP/UDP/IP Stream,Megaco,SS7 Signalling Gateway,Megaco,Media Gateway Controller,PSTN Trunks,VoI

42、P Terminals,PSTN Originating or Tandem Switch(es),SS7 Network,M3UA/SCTP,SS7,SS7,TDM,TDM,M3UA/SCTP,SIP-T,85,学习交流PPT,CS：软交换结构 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

43、【十分之一】。占地是传统电路交换机的十分之一。,86,学习交流PPT,CS：MGC 媒体网关控制器的功能,Contains all call control intelligence Implements call level features (forward, transfer, conference, hold, ),87,学习交流PPT,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）

44、MGCP 协议 （过去使用）,CS：MGC 媒体网关控制器协议,88,学习交流PPT,CS: 软交换系统组成与功能,Megaco Protocol,89,学习交流PPT,H.248,IP (or ATM) Network,PBX/CO,PBX/CO,Media Gateway,Device control,Device control,IP Phone Media Gateway,Telephone/Residential Media Gateway,PSTN trunking Media Gateway,PSTN line Media Gateway,PBX Media Gateway,Me

45、dia Gateway【媒体网关】: 功能与分类,Connection and device control No call processing, no call model Service-independent,90,学习交流PPT,CS: Signaling Gateway【信令网关】：功能,Signaling Gateways provide interaction between the SS7 network and Media Gateway Controllers. Convert SS7 to IP packets Convert IP to SS7 packets Sig

46、naling transport (SS7, SIP-T, Q.931) Extremely secure Extremely fault tolerant,91,学习交流PPT,Media GW Controller,Trunk Gateway,Megaco/ H.248,Virtual Switch,Sigtrans,SIP, H.323,PBX,D-channel,B-channels,PRI,Virtual Switch,RTP,Sigtrans,Signaling Gateway,Signaling Gateway,SS7,CO,Sigtrans,Sigtrans,The Inter

47、net,SS7 Network,CS: Signaling Gateway【信令网关】- 2,92,学习交流PPT,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SS7 SIP 信令是最佳选择,93,学习交流PPT,SS7 Architecture 【专用网络：无法共享】,94,学习交流PPT,SS7：ISUP Call Establishment/Release,95,学习交流PPT,SIP Protocol 【基于IP网络文本信令】,SIP,Audio Codec G.711 G.723 G.729,Video Codec H.261 H.263,RTP,RTCP,LAN Interface,TCP,IP,UDP,96,学习交流PPT,SIP Architecture,A signaling protocol The setup, modification, and tear-down of multimedia sessions SIP + SDP Describe the session characteristics to potential session participants Separate signaling and media streams S