TCPIP协议原理教学课件：Chapter 9 User Datagram Protocol(UDP)

1、Transport Layer ProtocolTransport Layer protocol: To serve as the intermediary between the application programs and the network operationsResponsibilities To create a process-to-process communicationTo provide a control mechanism at the transport layerflow control & error controlTo provide a connect

2、ion mechanism for the processesData stream2 Protocols for transport layerTransmission Control Protocol，TCPUser Datagram Protocol，UDP7/15/20221TCP/IP Protocol SuiteChapter 9 UDPProcess-to-process communicationUser datagramChecksumUDP operationUse of UDPUDP package7/15/20222TCP/IP Protocol SuiteProces

3、s-to-Process Comm.Internet进程Process进程ProcessDomain of IP protocolDomain of transport protocolsIP地址协议端口（port）端点（endpoint）7/15/20223TCP/IP Protocol SuiteIP entityTransport Layerprotocol entityPort Numbers212000( 21 )( 23 )( 80 )Process1Process2Process3803450236490IP Address7/15/20224TCP/IP Protocol Su

4、iteProcess-to-Process CommunicationUDP负责将IP数据报交付给适当的进程Process（进程）: a running application programA computer can run several processes at the same time C/S application model Client: a process on the local host which needs servicesSever: a process on the remote host which provides the servicesFor Proce

5、ss-to-Process Communication, must define the:Local host (IP), local process (Port Number)Remote host (IP), remote process (Port Number)7/15/20225TCP/IP Protocol SuitePort Numbers VS. C/SPort number: to define the processesEphemeral port number（短暂端口号）: can be chosen randomly by the client processWell

6、-known port number（熟知端口号）: is universal port number for server process传输协议Data1352000Data1352000传输协议1352000ClientServer多目标并发通信7/15/20226TCP/IP Protocol SuiteIP Address & Port Number1352001135200113IP headerTransportprotocolheaderPortnumberServer Processes 21807/15/20227TCP/IP Protocol SuiteIANA Rang

7、esWell-known portsAssigned and controlled by IANARegistered portsNot assigned or controlled by IANACan only be registered with IANA to prevent duplicationDynamic portsNeither controlled nor registeredCan be used by any process010231024491514915265535Well-knownRegisteredDynamicPort number7/15/20228TC

8、P/IP Protocol SuiteWell-known Ports/assignments/port-numbersThe well-known Ports on most systems can only be used by system (or root) processes or by programs executed by privileged usersTo the extent possible, some port assignments are both used with the TCP and UDPExample：port 53（DNS）7/15/20229TCP

9、/IP Protocol SuiteSocket （套接字）Addresses(IP address, Port number) Socket AddressProcess-to-process communication needs 2 Socket Addresses客户套接字地址服务器套接字地址7/15/202210TCP/IP Protocol SuiteChapter 9 UDPProcess-to-process communicationUser datagramChecksumUDP operationUse of UDPUDP package7/15/202211TCP/IP

10、 Protocol SuiteUser DatagramUser Datagram Protocol，UDPRFC 768，用户数据报协议IPLANsMANsWANsICMPIGMPARPRARPNetworkLayerNetworkAccess LayerApplication LayerTCPUDPTransportLayer7/15/202212TCP/IP Protocol SuiteIP headerIP dataProtocol = 17User Datagram FormatUDP HeaderSource port number16 bitsDestination port n

11、umber16 bitsTotal length16 bits（065535）Checksum16 bitsDataThe length of the data can be between 0 and 65507 bytes65507 = 65535 IP headerUDP header208IP headerIP data7/15/202213TCP/IP Protocol SuiteChapter 9 UDPProcess-to-process communicationUser datagramChecksumUDP operationUse of UDPUDP package7/1

12、5/202214TCP/IP Protocol SuiteChecksumUDP checksum与IP校验和的计算方法相同校验内容不同，包括三个部分：Pseudo header + UDP header + DataPseudo header（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7/15/202215TCP/IP Protocol SuitePseudo Header FormatProtocolAll 0sUDP total lengt

13、hDestination IP addressSource IP addressSource port numberDest. port numberUDP total lengthChecksumDataPseudoheaderHeader 7/15/202216TCP/IP Protocol SuiteChapter 9 UDPProcess-to-process communicationUser datagramChecksumUDP operationUse of UDPUDP package7/15/202217TCP/IP Protocol SuiteUDP OperationA

14、 connectionless, unreliable transport protocolTo create a process-to-process communicationConnectionless: 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No flow controlA litter error control: 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7/15/202218TCP/IP Protocol SuiteEncapsulation & Decapsulation7/15/20221

15、9TCP/IP Protocol SuiteQueues in UDP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7/15/202220TCP/IP Protocol SuiteMultiplexing & Demultiplexing7/15/202221TCP/IP Protocol SuiteChapter 9 UDPProcess-to-process communicationUser datagramChecksumUDP operationUse of UDPUDP package7/15/202222TCP/IP Protocol SuiteUse of UD

16、P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IP phone，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port x，提供服务客户端：动态绑定任意port n，向服务器port x发出请求，获得服务响应7/15/202223TCP/IP Protocol SuiteChapter 9 UDPProcess-to-process communicationUser datagramChecksumUDP operationUse of UDPUDP package7/15/202224TCP/IP Protocol SuiteUDP Package7/15/202225TCP/IP Protocol SuiteDiscussion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