TCPIP协议原理英文版课件：Chapter 9 User Datagram Protocol(UDP)

2022/10/29TCP/IPProtocolSuite1TransportLayerProtocolTransportLayerprotocol:ToserveastheintermediarybetweentheapplicationprogramsandthenetworkoperationsResponsibilitiesTocreateaprocess-to-processcommunicationToprovideacontrolmechanismatthetransportlayerflowcontrol&errorcontrolToprovideaconnectionmechanismfortheprocessesDatastream2ProtocolsfortransportlayerTransmissionControlProtocol，TCPUserDatagramProtocol，UDP2022/10/29TCP/IPProtocolSuite2Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2022/10/29TCP/IPProtocolSuite3Process-to-ProcessComm.Internet进程Process进程ProcessDomainofIPprotocolDomainoftransportprotocolsIP地址协议端口（port）端点（endpoint）＋2022/10/29TCP/IPProtocolSuite4IPentityTransportLayer

protocolentityPortNumbers212000(21)(23)(80)Process1Process2Process3803450236490IPAddress2022/10/29TCP/IPProtocolSuite5Process-to-ProcessCommunicationUDP负责将IP数据报交付给适当的进程Process（进程）:arunningapplicationprogramAcomputercanrunseveralprocessesatthesametimeC/SapplicationmodelClient:aprocessonthelocalhostwhichneedsservicesSever:aprocessontheremotehostwhichprovidestheservicesForProcess-to-ProcessCommunication,mustdefinethe:Localhost(IP),localprocess(PortNumber)Remotehost(IP),remoteprocess(PortNumber)2022/10/29TCP/IPProtocolSuite6PortNumbersVS.C/SPortnumber:todefinetheprocessesEphemeralportnumber（短暂端口号）:canbechosenrandomlybytheclientprocessWell-knownportnumber（熟知端口号）:isuniversal

portnumberforserverprocess传输协议Data1352000Data1352000传输协议1352000ClientServer……多目标并发通信Well-knownportsusedwithUDP2022/10/29TCP/IPProtocolSuite72022/10/29TCP/IPProtocolSuite8IPAddress&PortNumber1352001135200113IPheaderTransportprotocolheaderPortnumber…ServerProcesses21802022/10/29TCP/IPProtocolSuite9IANARangesWell-knownportsAssignedandcontrolledbyIANARegisteredportsNotassignedorcontrolledbyIANACanonlyberegisteredwithIANAtopreventduplicationDynamicportsNeithercontrollednorregisteredCanbeusedbyanyprocess010231024491514915265535Well-knownRegisteredDynamicPortnumber2022/10/29TCP/IPProtocolSuite10Well-knownPorts/assignments/port-numbersThewell-knownPortsonmostsystemscanonlybeusedbysystem(orroot)processesorbyprogramsexecutedbyprivilegedusersTotheextentpossible,someportassignmentsarebothusedwiththeTCPandUDPExample：port53（DNS）2022/10/29TCP/IPProtocolSuite11Socket（套接字）Addresses(IPaddress,Portnumber)SocketAddress——todefinetheS/CprocessuniquelyProcess-to-processcommunicationneeds2SocketAddresses客户套接字地址服务器套接字地址2022/10/29TCP/IPProtocolSuite12Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2022/10/29TCP/IPProtocolSuite13UserDatagramUserDatagramProtocol，UDPRFC768，用户数据报协议IPLANsMANsWANsICMPIGMPARPRARPNetworkLayerNetworkAccessLayerApplicationLayerTCPUDPTransportLayer2022/10/29TCP/IPProtocolSuite14IPheaderIPdataProtocol=17UserDatagramFormatUDPHeaderSourceportnumber16bitsDestinationportnumber16bitsTotallength16bits（0～65535）Checksum16bitsDataThelengthofthedatacanbebetween

0and65507bytes65507=65535––IPheaderUDPheader208IPheaderIPdata2022/10/29TCP/IPProtocolSuite15Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2022/10/29TCP/IPProtocolSuite16ChecksumUDPchecksum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+DataPseudoheader（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ChecksumOptional减少高可靠性网络上的传输开销2022/10/29TCP/IPProtocolSuite17PseudoHeaderFormatProtocolAll0sUDPtotallengthDestinationIPaddressSourceIPaddressSourceportnumberDest.portnumberUDPtotallengthChecksumDataPseudoheaderHeader2022/10/29TCP/IPProtocolSuite18Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2022/10/29TCP/IPProtocolSuite19UDPOperationAconnectionless,unreliabletransportprotocolTocreateaprocess-to-processcommunicationConnectionless: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NoflowcontrolAlittererrorcontrol: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2022/10/29TCP/IPProtocolSuite20Encapsulation&Decapsulation2022/10/29TCP/IPProtocolSuite21QueuesinUDP队列是与端口相关联在一起的进程入队列/出队列or进程入队列2022/10/29TCP/IPProtocolSuite22Multiplexing&Demultiplexing2022/10/29TCP/IPProtocolSuite23Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2022/10/29TCP/IPProtocolSuite24UseofUDP简单、简短的应用简单的请求-响应通信，如查询操作、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2022/10/29TCP/IPProtocolSuite25Chapter9UDPProcess-to-processcommunicationUserdatagramChecksumUDPoperationUseofUDPUDPpackage2022/10/29TCP/IPProtocolSuite26UDPPackage2022/10/29TCP/IPProtocolSuite27Discussion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