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進程Process進程ProcessDomain of IP protocolDomain of transport protocolsIP地址協(xié)議端口（port）端點（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負(fù)責(zé)將IP數(shù)據(jù)報交付給適當(dāng)?shù)倪M程Process（進程）: 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（短暫端口號）: can be chosen randomly by the client processWell

6、-known port number（熟知端口號）: is universal port number for server process傳輸協(xié)議Data1352000Data1352000傳輸協(xié)議1352000ClientServer多目標(biāo)并發(fā)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客戶套接字地址服務(wù)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，用戶數(shù)據(jù)報協(xié)議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與IP校驗和的計算方法相同校驗內(nèi)容不同，包括三個部分：Pseudo header + UDP header + DataPseudo header（偽首部）根據(jù)IP首部的部分信息形成不會與UDP報文一起發(fā)送到網(wǎng)絡(luò)上進一步確保UDP報文送到正確主機(目的IP地址正確)的正確端口上Checksum Optional減少高可靠性網(wǎng)絡(luò)上的傳輸開銷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: 不同路徑、不編號、面向報文面向報文：不支持?jǐn)?shù)據(jù)流，也不支持分段、重組No flow controlA litter error control: checksum出錯，悄悄丟棄對IP協(xié)議增強主機多目標(biāo)通信的區(qū)分，允許多個通信并發(fā)進行而不會發(fā)生混淆7/15/202218TCP/IP Protocol SuiteEncapsulation & Decapsulation7/15/20221

15、9TCP/IP Protocol SuiteQueues in UDP隊列是與端口相關(guān)聯(lián)在一起的進程入隊列/出隊列 or 進程入隊列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簡單、簡短的應(yīng)用簡單的請求-響應(yīng)通信，如查詢操作、網(wǎng)絡(luò)管理IP phone，利用UDP快捷的特點適用于具有內(nèi)部流控和差錯控制的進程，如TFTP組播或廣播應(yīng)用某些路由協(xié)議，如RIP一般使用方式 客戶/服務(wù)器模式服務(wù)端：固定守候在特定port x，提供服務(wù)客戶端：動態(tài)綁定任意port n，向服務(wù)器port x發(fā)出請求，獲得服務(wù)響應(yīng)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偽首部使得IP層和UDP層的界線模糊不清考查UDP協(xié)議軟件在發(fā)送報文時如何計算校驗和UDPIPI1NI1NI2NI3I2I317（dIP，dPort，Data）sPort封裝UDP計算CS計算