TCPIP_Chapter9UserDatagramProtocol(UDP).

TCP/IP协议原理吴凡通信与信息工程学院网络工程系E-mail:[e-mail]:61830521(O)2020/1/10TCP/IPProtocolSuite2TransportLayerProtocolTransportLayerprotocol:ToserveastheintermediarybetweentheapplicationprogramsandthenetworkoperationsResponsibilitiesTocreateaprocess-to-processcommunicationToprovideacontrolmechanismatthetransportlayerflowcontrol&errorcontrolToprovideaconnectionmechanismfortheprocessesDatastream2ProtocolsfortransportlayerTransmissionControlProtocol，TCPUserDatagramProtocol，UDP2020/1/10TCP/IPProtocolSuite3Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2020/1/10TCP/IPProtocolSuite4Process-to-ProcessComm.Internet进程Process进程ProcessDomainofIPprotocolDomainoftransportprotocolsIP地址协议端口（port）端点（endpoint）＋2020/1/10TCP/IPProtocolSuite5IPentityTransportLayerprotocolentityPortNumbers212000(21)(23)(80)Process1Process2Process3803450236490IPAddress2020/1/10TCP/IPProtocolSuite6Process-to-ProcessCommunicationUDP负责将IP数据报交付给适当的进程Process（进程）:arunningapplicationprogramAcomputercanrunseveralprocessesatthesametimeC/SapplicationmodelClient:aprocessonthelocalhostwhichneedsservicesSever:aprocessontheremotehostwhichprovidestheservicesForProcess-to-ProcessCommunication,mustdefinethe:Localhost(IP),localprocess(PortNumber)Remotehost(IP),remoteprocess(PortNumber)2020/1/10TCP/IPProtocolSuite7PortNumbersVS.C/SPortnumber:todefinetheprocessesEphemeralportnumber（短暂端口号）:canbechosenrandomlybytheclientprocessWell-knownportnumber（熟知端口号）:isuniversalportnumberforserverprocess传输协议Data1352000Data1352000传输协议1352000ClientServer……多目标并发通信Well-knownportsusedwithUDP2020/1/10TCP/IPProtocolSuite82020/1/10TCP/IPProtocolSuite9IPAddress&PortNumber135200113193.14.26.75200113193.14.26.7IPheaderTransportprotocolheaderPortnumber…ServerProcesses21802020/1/10TCP/IPProtocolSuite10IANARangesWell-knownportsAssignedandcontrolledbyIANARegisteredportsNotassignedorcontrolledbyIANACanonlyberegisteredwithIANAtopreventduplicationDynamicportsNeithercontrollednorregisteredCanbeusedbyanyprocess010231024491514915265535Well-knownRegisteredDynamicPortnumber2020/1/10TCP/IPProtocolSuite11Well-knownPortsThewell-knownPortsonmostsystemscanonlybeusedbysystem(orroot)processesorbyprogramsexecutedbyprivilegedusersTotheextentpossible,someportassignmentsarebothusedwiththeTCPandUDPExample：port53（DNS）2020/1/10TCP/IPProtocolSuite12Socket（套接字）Addresses(IPaddress,Portnumber)SocketAddress——todefinetheS/CprocessuniquelyProcess-to-processcommunicationneeds2SocketAddresses客户套接字地址服务器套接字地址2020/1/10TCP/IPProtocolSuite13Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2020/1/10TCP/IPProtocolSuite14UserDatagramUserDatagramProtocol，UDPRFC768，用户数据报协议IPLANsMANsWANsICMPIGMPARPRARPNetworkLayerNetworkAccessLayerApplicationLayerTCPUDPTransportLayer2020/1/10TCP/IPProtocolSuite15IPheaderIPdataProtocol=17UserDatagramFormatUDPHeaderSourceportnumber16bitsDestinationportnumber16bitsTotallength16bits（0～65535）Checksum16bitsDataThelengthofthedatacanbebetween0and65507bytes65507=65535––IPheaderUDPheader208IPheaderIPdata2020/1/10TCP/IPProtocolSuite16Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2020/1/10TCP/IPProtocolSuite17ChecksumUDPchecksum与IP校验和的计算方法相同校验内容不同，包括三个部分：Pseudoheader+UDPheader+DataPseudoheader（伪首部）根据IP首部的部分信息形成不会与UDP报文一起发送到网络上进一步确保UDP报文送到正确主机(目的IP地址正确)的正确端口上ChecksumOptional减少高可靠性网络上的传输开销2020/1/10TCP/IPProtocolSuite18PseudoHeaderFormatProtocolAll0sUDPtotallengthDestinationIPaddressSourceIPaddressSourceportnumberDest.portnumberUDPtotallengthChecksumDataPseudoheaderHeader2020/1/10TCP/IPProtocolSuite19Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2020/1/10TCP/IPProtocolSuite20UDPOperationAconnectionless,unreliabletransportprotocolTocreateaprocess-to-processcommunicationConnectionless:不同路径、不编号、面向报文面向报文：不支持数据流，也不支持分段、重组NoflowcontrolAlittererrorcontrol:checksum出错，悄悄丢弃对IP协议增强主机多目标通信的区分，允许多个通信并发进行而不会发生混淆2020/1/10TCP/IPProtocolSuite21Encapsulation&Decapsulation2020/1/10TCP/IPProtocolSuite22QueuesinUDP队列是与端口相关联在一起的进程入队列/出队列2020/1/10TCP/IPProtocolSuite23Multiplexing&Demultiplexing2020/1/10TCP/IPProtocolSuite24Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2020/1/10TCP/IPProtocolSuite25UseofUDP简单、简短的应用简单的请求-响应通信，如查询操作(DNS)、网络管理IPphone，利用UDP快捷的特点适用于具有内部流控和差错控制的进程，如TFTP组播或广播应用某些路由协议，如RIP一般使用方式——客户/服务器模式服务端：固定守候在特定portx，提供服务客户端：动态绑定任意portn，向服务器portx发出请求，获得服务响应2020/1/10TCP/IPProtocolSuite26Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2020/1/10TCP/IPProtocolSuite27UDPPackage2020/1/10TCP/IPProtocolSuite28Discussion伪首部使得IP层和UDP层的界线模糊不清考查UDP协议软件在发送报文时如何计算校验和UDPIPI1NI1NI2NI3I2I317（dIP，dPort，Data）sPort封装UDP计算CS计算CS的困难：计算前需要知道sIP，但在IP选路前，sIP是未知的（sIP与选择的NI有关）计算步骤：1.封装成UDP送给IP层2.IP层完成选路，得到sIP，再送回UDP层3.UDP层计算CS，再送IP层UDP接