计算机网络体系结构外文翻译.docx

计算机网络体系结构外文翻译.docx

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计算机网络体系结构外文翻译

附录A

Withthenewnetworktechnologyandapplicationofthecontinuousrapiddevelopmentofthecomputernetworkshould.Useofbecomingincreasinglywidespread,theroleplayedbytheincreasinglyimportantcomputernetworksandhuman.Moreinseparablefromthelivesofthecommunity'srelianceonthemwillkeepgrowing.

Inorderforcomputerstocommunicate,theymustspeakthesamelanguageorprotocol.Intheearlydaysofnetworking,networksweredisorganizedinmanyways.Companiesdevelopedproprietarynetworktechnologiesthathadgreatdifficultiesinexchanginginformationwithotherorexistingtechnologies;sonetworkinterconnectionswereveryhardtobuild.Tosolvethisproblem,theInternationalOrganizationforStandardization（ISO）createdanetworkmodelthathelpsvendorstocreatenetworkscompatiblewitheachother.

Findingthebestsoftwareisnoteasy.Abetterunderstandingofwhatyouneedandaskingtherightquestionsmakesiteasier.Thesoftwareshouldbecapableofhandlingchallengesspecifictoyourcompany.Ifyouoperatemultipledistributioncenters,itmaybebeneficialtocreaterouteswithproductoriginatingfrommorethanonedepot.Fewsoftwareprovidersthough,arecapableofoptimizingroutesusingmultipledepots.Theprovidershouldbeabletosupportinstallationofitsproduct.Makesuretoclearlyunderstandwhattrainingandsoftwaremaintenanceisoffered.

Obviously,selectingtherightrouting/schedulingsoftwareiscriticallyimportant.Unfortunately,somecompaniesareusingsoftwarethatmaynotbebestsuitedtotheiroperation.Logisticsactiveswithresponsibilityforapprovingthesoftwareoughttobecomfortablethey'vemadetherightdecision.Itisimportanttorealizethatnotallrouting/schedulingsoftwareisalike！

Therequestionstoaskare：

Whichoperatingsystemisused？

Howeasyisthesoftwaretouse？

Hereisagoodwaytotell.Askifitsgraphicaluserinterface（GUI）isflexible.Findoutaboutinstallationspeed-howlongdoesittake？

Isthesoftwareabletoroutethirdpartycustomerswithyourcorebusiness？

Whenwasthesoftwareoriginallyreleasedandwhenwasitlastupgraded？

In1984,ISOreleasedtheOpenSystemsInterconnection（OSI）referencemodel,whichisawell-definedsetofspecificationsthatensuresgreatercompatibilityamongvarioustechnologies.Infact,OSIisadescriptionofnetworkcommunicationthateveryonerefersto.Itisnottheonlynetworkmodel,butithasbecometheprimarymodelfornetworkcommunication.Youwillseefurtherinthischapter,thattheTCP/IPmodelisonlyareducedversionoftheOSImodel.TheOSImodelconsistsofsevenlayers,eachillustratingaparticularnetworkfunction.

meanwhile,ASPcontinuestoevolve.WiththearrivalofthemillenniumcamethearrivalofASPversion3.0.Version3.0wasreleasedalongwithInternetInformationServer（IIS）version5.0aspartofthehighlyanticipatedMicrosoftWindows2000.Byfar,themostimportantnewfeatureofversion3.0istheadditionofaseventh,intrinsicobjectcalledASPErrorwhichshouldgreatlysimplifyerrorhandling.OthernewfeaturesincludetheadditionofthreenewmethodstotheServerobject,andtwonewmethodstoboththeApplicationobjectandtheSessionobject.

Whenprogrammersdesignanimageeditorforexample,theydon'thavetothinkaboutaddingOSILayer7capabilitiestothatsoftware,becauseithasnoneedforcommunicationwithothercomputers.Ontheotherhand,whencreatinganFTPclient,theymustaddcommunicationcapabilitiestothatsoftware.AtLayer7weusuallyfindTelnet,FTP,HTTP,SMTP,SNMP,orSSH.Whenwesay,ForExample,Layer7filtering,werefertofilteringapplicationdata,regardlessofwhatportorcomputeritmaycomefrom.

OSIwillbeacomputernetworkarchitecture（architecture）isdividedintothefollowingseven：

Thefirstlayer：

physicallayer（PhysicalLayer）,providescommunicationsequipmentforthemechanical,electricalandfunctionalcharacteristicsandprocessfortheestablishment,maintenanceandremovalofthephysicallinkconnection.Specifically,theprovisionsofthemechanicalpropertiesrequiredfornetworkconnectivityconnectordimensions,pinnumberandordersituation,etc.;theprovisionsoftheelectricalcharacteristicsofthephysicalconnectioninthebitstreamtransmissionlinesignallevelofthesize,impedancematching,transferratefromtheconstraints;featuresreferstothedistributionofthevarioussignalstotheexactmeaningofthesignal,thatisthedefinitionoftheDTEandDCEfunctionbetweenthevariouslines;ordercharacteristicsofthedefinitionoftheuseofbitstreamsignaltransmissionlinesforagroupofrulesreferstothephysicalconnectionoftheestablishment,maintenance,exchangeofinformation,DTEandDCEonthecircuitondouble-actionseries.Inthislayer,dataunitsknownasbits（bit）.Belongtothetypicaldefinitionofthephysicallayerspecificationincluded：

EIA/TIARS-232,EIA/TIARS-449,V.35,RJ-45andsoon.

Thesecondlayer：

datalinklayer（DataLinkLayer）：

inthephysicallayerbitstreamtoprovideservicesbasedonadjacentnodebetweenthedatalink,throughtheprovisionoferrorcontroldataframe（Frame）inthechannelerror-freetransmission,andtheactionoftheseriescircuit.Datalinklayerinthephysicalmediaisnotreliabletoprovidereliabletransmission.Theroleofthislayerinclude：

addressingthephysicaladdress,dataframing,flowcontrol,dataerror,suchasre-issued.Inthislayer,dataunitsknownastheframe（frame）.Datalinklayerprotocol,includingrepresentativesof：

SDLC,HDLC,PPP,STP,suchasframerelay.

Thethirdlayeristhenetworklayer

Inthecomputernetworktocommunicatebetweentwocomputersmaybealotofdatalinkmayalsogothroughalotofcommunicationsubnet.Networklayerofthetaskistochooseasuitableinter-networkroutingandswitchingnodes,toensuretimelydeliveryofdata.Networklayerwillprovidethedatalinklayerpacketframecomponents,includingnetworklayerinthepackageheader,whichcontainsthelogicaladdressinformation--thesourcesiteanddestinationsiteaddressofthenetworkaddress.Ifyou'retalkingaboutanIPaddress,thenyouareindealingwiththeproblemofLayer3,whichis“datapackets”,ratherthanlayer2ofthe“frame.”IPislayer3partoftheproblem,inadditiontoanumberofroutingprotocolsandARP（ARP）.AllthingsrelatedtoroutinginLayer3processing.AddressresolutionandroutingisanimportantobjectiveofLevel3.NetworklayercanalsoachievecongestioncontrolfeaturessuchasInternetinterconnection.Inthislayer,datapacketsastheunit（packet）.Representativesofthenetworklayerprotocol,including:

IP,IPX,RIP,OSPF,etc…

Thefourthtieristhetransportlayerprocessinformation.Atfourthfloorunit,alsoknownasdatapackets（packets）.However,whenyoutalkaboutTCPprotocol,suchasconcreteandspecificwhenthename,TCPdataunitknownasparagraph（segments）andtheUDPprotocoldataunitreferredtoas“datagram（datagrams）”.Thislayerisresponsibleforobtainingalltheinformation,therefore,itmustbetrackingdatacelldebris,out-of-orderpacketsarriveinthetransferprocessandotherpossiblerisk.No.4fortheupperlayertoprovideend-to-end（theend-usertoend-users）ofatransparentandreliabledatatransmissionservices.Transparentbymeansoftransmissionistransmittedinthecommunicationprocessoftheupperlayershieldingthecommunicationtransmissionsystemdetails.RepresentativesoftheTransportProtocol：

TCP,UDP,SPX,etc…

Thefifthlayeristhesessionlayer

Thislayercanalsobeknownasthedialoguemeetingbetweenlayersorlayer,inthesessionlayerandabovethehigh-level,thedatatransmissionisnolongertheothernamedunits,knowncollectivelyasthemessage.Sessionlayerdoesnotparticipateinspecifictransmission,Itprovides,includingaccesstoauthenticationandsessionmanagement,includingtheestablishmentandmaintenanceofmechanismsforcommunicationbetweenapplications.Iftheservertoverifyuserloginiscompletedbythesessionlayer.

ThesixthlayerisPresentationLayer

Themainsolutiontosupportthislevelofinformationthattheproblemofsyntax.Fortheexchangeofdatawillbesuitableforauserfromtheabstractsyntax,intoasystemsuitablefortheuseofOSItransfersyntax.Toprovideformattingandconversionofthatdataservices.Datacompressionanddecompression,encryptionanddecryptionsothatthelayersareresponsiblefor.

Theseventhlayerapplicationlayer,applicationlayerfortheoperatingsystem,applicationsornetworkservicesaccessthenetworkinterface.Agreementonbehalfoftheapplicationlayer,including:

Telnet,FTP,HTTP,SNMP,etc..

ThroughtheOSIlayers,informationfromacomputersoftwareapplicationfortransfertoanotherapplication.Forexample,computerAontheapplicationtosendinformationtothecomputerapplicationB,thenAcomputerapplicationininformationneedtobesenttotheApplicationLayer（seventhlayer）,andthenthislayerwillbesenttothatlevelofinformation（sixthfloor）,indicatingthatthedatalayerwillbetransferredtothesessionlayer（fifthlayer）,andsocontinueuntilthephysicallayer（firstlayer）.Inthephysicallayer,dataisplacedinthephysicalnetworkmediaandsenttocomputerB.ThephysicallayerofcomputerBtoreceivedatafromthephysicalmedia,andthensendinformationuptodatalinklayer（secondlayer）,datalinklayerandthentothenetworklayer,untiltheinformationinordertoarriveattheapplicationlayerofcomputerB.Finally,theapplicationlayerofcomputerBandthentheapplicationinformationtothereceivingen