数据通信基础

1、数据通信基础和竞争对手分析 1三种网络的基本特征PSTN以 64K 时隙为基础的线路交换限制了高带宽的应用过渡性的解决方案多时隙捆绑革命性的解决方案宽带交换技术CATV单向、模拟、区域性是多种应用的技术障碍有限的双向改造可以解决部分的数据传输，对语音则无能为力数字电视的标准化才会引发真正的革命数据网络以包交换为基础设计之初以满足窄带应用为基础，可以满足多种通信模式的要求已经迅速发展成为可以满足各种应用的技术终端设备将从单一的计算机向多种终端演化2世界通信标准化组织Open versus de-factoEnsure interoperabilityStandards bodies:ISO fo

2、cuses on data communication interfacesITU-TSS focuses on telecommunications and networking standards (e.g. FR, ATM, B-ISDN)ANSI coordinates with ISO for the US standardsIEEE focuses on Local Area Networks (e.g. IEEE 802.3)EIA focuses on physical connectors (e.g. RS232)3OSI/ISO 模型OSI ModelEnd user抯 a

3、ccess to networkFormats data for presentation to userLogical sessions between end usersLogical connections for transfer of data between end users (e.g. TCP, SPX)Addressing and routing (e.g. IP, IPX, X.25 PLP)Creates and recognizes message boundaries and checks for errorsTransmits data bits over comm

4、unication circuitApplicationPresentationSessionTransportNetworkData LinkPhysical4网络协议的模型和层次OSI ModelApplicationPresentationSessionTransportNetworkData LinkPhysical1234567ApplicationUtilitiesTCP UDPIPNetworkAccess(e.g. IEEE 802.3)TCP/IP SPXIPXData Link(e.g. IEEE 802.3)IPX/SPXApplicationUtilities5线路传输

5、的主要标准Medium SONET STMDS0ChannelsSpeed OC-1 STS-1672 51.840 OC-3 STS-3 STM-12016 155.520OC-9 STS-9 6048 466.560 OC-12 STS-12 STM-48064 622.080OC-18 STS-18 12,096 933.120OC-24 STS-24 16,1281.244 GbpsOC-36 STS-3624,1921.866 GbpsOC-48 STS-48 STM-1632,2562.488 GbpsOC-96 STS-96 64,5124.976 GbpsOC-192 STS-

6、192 STM-64 129,024 9.952Gbps6通讯的实现举例ServerHubRouterHubRouterF/REthernetEthernetFrame RelayApplication(e.g. Email)Transport (TCP)Network (IP)Data Link (E)Physical UTP-3IPEcat.3IPFRRS 232IPFRRS 232IPEcat.5Application(e.g. Email)Transport (TCP)Network (IP)Data Link (E)Physical UTP-57局域网技术HUBStationStat

7、ionStationPrint ServerNetwork PrinterDatabase ServerAccess ServerTerminal Server8以太网的桢格式Developed jointly by Digital, Intel, and XeroxVery similar to IEEE 802.3Relies on special pattern of SYN characters to mark the start of frameLength indicates the length of message portion of frame (Max 1500 byte

8、s)Ethernet FrameDestinationAddress6 bytesSourceAddress6 bytesLength2 BVariablePayloadVariableCRC-324 bytes9X.25 的协议和桢结构ApplicationPLPLAP-BX.21 bis (232C, V.35)X.25Bit StreamLayer 1Layer 2(Frame)FlagControl& AddressDataFCSFlagUser DataHeaderLayer 3(Packet)DCEDTEDCEDTEX.25X.25Virtual CircuitPDN10Frame

9、 Relay 网络结构RouterSwitchSwitchSwitchSwitchSwitchSwitchFrame Relay NetworkRouter2. Up to 50 MbpsTCP does End-to-End AcknowledgmentUser data (e.g. TCP/IP packets)up to 8187 OctetsLayer 3 Packet3. Efficient with LAN protocols10 Mbps10 MbpsFRUNIFRUNI11Frame Relay 桢结构User dataIPInformation Field(up to 818

10、7 octet)address &ControlFlag01111110FCSFlag01111110TCPExample: TCP/IP over Frame Relay87654321Octet12DLCIDLCIFECNBECNDEEAC/READLCI: Data Link Connection IdentifierC/R: Command/Response (not used)EA: Address ExtensionDE: Discard EligibilityFECN: Forward Explicit Congestion NotificationBECN: Backward

11、Explicit Congestion Notification12TCP/IP协议组中的主要协议ETHERNET TR FDDI PPP ATM FR1IPROUTE DATAGRAMS2TCPEND TO ENDCONNECTIONSUDPSINGLE MESSAGES34WWWFTPNEWSTELNETSMTPNFSDNSSNMP13TCP/IP信息的封装过程ApplicationTCPIPNetworkAccess(e.g. IEEE 802.3)MessagePacketPacketPacketPacketPacketTCP Header- TCP port numbers (app

12、lication)- Sequence numbers- AcknowledgmentPacketIP Header- Source and Destination Address- Time To LivePacketEthernet Header- MAC source anddestination address14Internet IP协议的结构netidClass A0 to 127024 bits7 bitsClass B128 to 19182431hostidClass C192 to 25431hostidnetid1hostidnetid1010Example: is a

13、class B networkFirst octet is assigned by the network information center14 bits16 bits21 bits8 bitsOctet 4Octet 1Octet 2Octet 3Octet 4Octet 1Octet 2Octet 3Octet 4Octet 1Octet 2Octet 315网络中的设备BridgesBest for local traffic segmentationAdvantagePlug and PlayProvide simple filteringLimitationLow Broadca

14、st controlLimited WAN capabilityLow securityRoutersBest for wide area networksAdvantageConnect dissimilar type of networksProvide Traffic filteringProvide load sharing links.High security (fireWall)LimitationComplex configurationLow LatencySwitchesBest for dedicating bandwidth to users or serversAdv

15、antagePlug and PlayLow latencyLimitationNo Broadcast controlNo WAN capabilityLow securityNo traffic filtering16网络中的路由表Routing is the process of determining the route/path through the network that a message will travel from the sending computer to the receiving computerRouting occurs at several level

16、s (e.g. WAN switches, routers)SwitchSwitchSwitchSwitchSwitchSwitchSwitchABCDFGERouting Table For B17路由器在网络中的位置和作用NetworkNetworkNetworkRouting TableDestination NetworkNext hopRouting TableDestination NetworkNext hopMAGELLANMAGELLANABIP is connectionlessRouting tables are generated by protocols such a

17、s RIP and OSPF18网络的市场分布Carriers or service providers (56%)Global carriersNational carriersSpecial service providers (e.g. Swift, SITA,.)Enterprise networks (44%)Financial Companies (20%)Government departments (6%)Manufacturers (6%)Transportation (6%)Utilities (3%)Academic and Medical Institutions (3

18、%)19层出不穷的接入手段20各种接入手段的速度上行速率下行速率21多种接入技术存在和选择已经埋设的基础设施在原有设施上进行改造以适应新的应用和竞争需求不同的应用拉、退以及不同速率、质量因素不同的人口密度各种技术的成本不同不同的地理环境不同的商业环境22aDSL 接入原理DSLAMATU-RATU-RATU-RPsPsPsATU-CATU-CATU-CLE C&C 08A4 接口数字广播数据网络网络管理服务内容区局 端用户区23ADSL 频谱的利用ADSL调制解调器的频谱利用的划分0 4 20 50 140 150 500 1100频率(KHz)下行上行传统电话频谱1.5Mb/s6.3Mb/s

19、24aDSL 中的主要概念DSLAM DSL接入复用器Ps POTS 分路器ATU-C ADSL传输单元中心ATU-R ADSL传输单元远端CAP、DTM aDSL的两种调制方式xDSL 是利用双绞线中的不同频段分别传输语音、上行、下行信号的25 xDSL 的业务定位不适合将来的数字电视市场主要视频业务集中在VOD和 nVOD高速Internet 接入通明高速数字传输xDSL 必需处于端局，不能跨PSTN局，限制了其覆盖范围和灵活性263Com TotalControlFront located NACHot Swapable NAC LED indicator show statusVart

20、ical card easy coolingRear located NICFlexible NIC card provide multiple interfaceSecure wiring Lock back cabinet for more security27TotalControl的逻辑结构E1Acceess Serer30 x 56KModem30 x 56KModem30 x 56KModem30 x 56KModem30 x 56KModem30 x 56KModemE1E1E1E1E1第三代产品：分布中继处理，满足大型ISP的 多E1线路的拨号接入及新应用的需求特点：每个E1单

21、独处理， 提供充足的处理能力， 满足今后新技术的要求。 E1之间不共享 TDM 总线， 克服E1间可能的干扰。 灵活的中继资源 利用能力， 强大的后处理能力，如 Hiper Router 和 Edge Server。 支持 VOIP， FOIP 及多媒体应用。28TotalControl板位图HIPerARCNICTDM BusPacket BusNICDSPCardNICDSPCardNICDSPCardNICDSPCardNICDSPCardNICDSPCardNICDSPCardNICDSPCardNICDSPCardNICDSPCardNICDSPCardNICDSPCardNICDS

22、PCardNICDSPCardHIPerARCNICDistributed TrunkingRedundant Access Routers29TotalControl主要弱点分析每个E1单独处理，没有TDM交换功能，不能实现中继合群ISDN Call 需要Modem卡，经济性不好满负荷运行效率低下或者接通率低优点：在网络上应用比较多30Ascend Max TNT43.5 cmJEDEC DRAM SlotTwo Flash PCMCIA SlotsEthernetIntershelfExpansion BusPortsConsole Port 1234567890AC or DC Powe

23、r SupplyAC or DC Power SupplyTDM BUS (64Mbps FDX)CELL BUS (155Mbps FDX)Control BUS (10 Mbps)29.5 cm31Max TNT 135670AC or DC Power SupplyAC or DC Power SupplyMain Power Supply(AC or DC)Redundant Power Supply(AC or DC)JEDEC DRAM SlotTwo Flash PCMCIA SlotsEthernetMultishelfExpansion BusPorts16Expansion SlotsConsole PortAlarm Contact14”17