计算机毕设外文翻译

外文翻译原文及译文学院计算机学院专业班级学号姓名指导教师负责教师沈阳航空航天大学2011年6月IntroductiontoTCP/IPABSTRACTTCPandIPweredevelopedbyaDepartmentofDefense(DOD)researchprojecttoconnectanumberdifferentnetworksdesignedbydifferentvendorsintoanetworkofnetworks(theInternet).Itwasinitiallysuccessfulbecauseitdeliveredafewbasicservicesthateveryoneneeds(filetransfer,electronicmail,remotelogon)acrossaverylargenumberofclientandserversystems.SeveralcomputersinasmalldepartmentcanuseTCP/IP(alongwithotherprotocols)onasingleLAN.TheIPcomponentprovidesroutingfromthedepartmenttotheenterprisenetwork,thentoregionalnetworks,andfinallytotheglobalInternet.Onthebattlefieldacommunicationsnetworkwillsustaindamage,sotheDODdesignedTCP/IPtoberobustandautomaticallyrecoverfromanynodeorphonelinefailure.Thisdesignallowstheconstructionofverylargenetworkswithlesscentralmanagement.However,becauseoftheautomaticrecovery,networkproblemscangoundiagnosedanduncorrectedforlongperiodsoftime.Aswithallothercommunicationsprotocol,TCP/IPiscomposedoflayers:IP-isresponsibleformovingpacketofdatafromnodetonode.IPforwardseachpacketbasedonafourbytedestinationaddress(theIPnumber).TheInternetauthoritiesassignrangesofnumberstodifferentorganizations.Theorganizationsassigngroupsoftheirnumberstodepartments.IPoperatesongatewaymachinesthatmovedatafromdepartmenttoorganizationtoregionandthenaroundtheworld.TCP-isresponsibleforverifyingthecorrectdeliveryofdatafromclienttoserver.Datacanbelostintheintermediatenetwork.TCPaddssupporttodetecterrorsorlostdataandtotriggerretransmissionuntilthedataiscorrectlyandcompletelyreceived.Sockets-isanamegiventothepackageofsubroutinesthatprovideaccesstoTCP/IPonmostsystems.1IntroductionTheArmyputsoutabidonacomputerandDECwinsthebid.TheAirForceputsoutabidandIBMwins.TheNavybidiswonbyUnisys.ThenthePresidentdecidestoinvadeGrenadaandthearmedforcesdiscoverthattheircomputerscannottalktoeachother.TheDODmustbuildanetworkoutofsystemseachofwhich,bylaw,wasdeliveredbythelowestbidderonasinglecontract.TheInternetProtocolwasdevelopedtocreateaNetworkofNetworks(theInternet).IndividualmachinesarefirstconnectedtoaLAN(EthernetorTokenRing).TCP/IPsharestheLANwithotheruses(aNovellfileserver,WindowsforWorkgroupspeersystems).OnedeviceprovidestheTCP/IPconnectionbetweentheLANandtherestoftheworld.Toinsurethatalltypesofsystemsfromallvendorscancommunicate,TCP/IPisabsolutelystandardizedontheLAN.However,largernetworksbasedonlongdistancesandphonelinesaremorevolatile.IntheUS,manylargecorporationswouldwishtoreuselargeinternalnetworksbasedonIBM'sSNA.InEurope,thenationalphonecompaniestraditionallystandardizeonX.25.However,thesuddenexplosionofhighspeedmicroprocessors,fiberoptics,anddigitalphonesystemshascreatedaburstofnewoptions:ISDN,framerelay,FDDI,AsynchronousTransferMode(ATM).Newtechnologiesariseandbecomeobsoletewithinafewyears.WithcableTVandphonecompaniescompetingtobuildtheNationalInformationSuperhighway,nosinglestandardcangoverncitywide,nationwide,orworldwidecommunications.TheoriginaldesignofTCP/IPasaNetworkofNetworksfitsnicelywithinthecurrenttechnologicaluncertainty.TCP/IPdatacanbesentacrossaLAN,oritcanbecarriedwithinaninternalcorporateSNAnetwork,oritcanpiggybackonthecableTVservice.Furthermore,machinesconnectedtoanyofthesenetworkscancommunicatetoanyothernetworkthroughgatewayssuppliedbythenetworkvendor.2.1AddressesEachtechnologyhasitsownconventionfortransmittingmessagesbetweentwomachineswithinthesamenetwork.OnaLAN,messagesaresentbetweenmachinesbysupplyingthesixbyteuniqueidentifier(theMACaddress).InanSNAnetwork,everymachinehasLogicalUnitswiththeirownnetworkaddress.DECNET,Appletalk,andNovellIPXallhaveaschemeforassigningnumberstoeachlocalnetworkandtoeachworkstationattachedtothenetwork.Ontopoftheselocalorvendorspecificnetworkaddresses,TCP/IPassignsauniquenumbertoeveryworkstationintheworld.ThisIPnumberisafourbytevaluethat,byconvention,isexpressedbyconvertingeachbyteintoadecimalnumber(0to255)andseparatingthebyteswithaperiod.Forexample,thePCLubeandTuneserveris130.13[e-mail]stanyonetogetassignmentofanumberforasmallClassCnetworkinwhichthefirstthreebytesidentifythenetworkandthelastbyteidentifiestheindividualcomputer.Theauthorfollowedthisprocedureandwasassignedthenumbers192.35.91.*foranetworkofcomputersathishouse.LargerorganizationscangetaClassBnetworkwherethefirsttwobytesidentifythenetworkandthelasttwobytesidentifyeachofupto64thousandindividualworkstations.Yale'sClassBnetworkis130.132,soallcomputerswithIPaddress130.132.*.*areconnectedthroughYale.TheorganizationthenconnectstotheInternetthroughoneofadozenregionalorspecializednetworksuppliers.Thenetworkvendorisgiventhesubscribernetworknumberandaddsittotheroutingconfigurationinitsownmachinesandthoseoftheothermajornetworksuppliers.Thereisnomathematicalformulathattranslatesthenumbers192.35.91or130.132intoYaleUniversityorNewHaven,CT.ThemachinesthatmanagelargeregionalnetworksorthecentralInternetroutersmanagedbytheNationalScienceFoundationcanonlylocatet