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.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
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