计算机英语（下篇共上中下3篇）

计算机英语（第三版）北京出版社Unit9ComputerNetworkTask9.1ComputerNetworkTask9.2NetworkArchitectureTask9.3NetworkTopologyTask9.4TypesofNetworks目录01020304directoryTask9.1

ComputerNetworkLearningObjectivesAftercompletingthistask,youshouldbeabletodefinethetermofcomputerNetwork.LearningPreparationKeyterms—networkRelativespecializedknowledge;InternetPlanandImplementStep1ReadRelativeKnowledge;Step2Requirestudentstograspthekeytermsinthistask;Step3Assessment.InquiryandDiscoveryThesimplestkindofnetworkcontainsjusttwocomputers.Youcanusethiskindofnetworktosharefiles,aprinteroranotherperipheraldevice,andevenanInternetconnection.Howcanweconnecttwocomputersthroughanetwork?Acomputernetworkisagroupofinterconnectedcomputers.Acomputernetworkisacollectionofcomputersanddevicesconnectedtooneanother.Thenetworkallowscomputerstocommunicatewitheachotherandshareresourcesandinformation.TheAdvancedResearchProjectsAgency(ARPA)designed“AdvancedResearchProjectsAgencyNetwork”(ARPANET)fortheUnitedStatesDepartmentofDefense.Itwasthefirstcomputernetworkintheworldinlate1960sandearly1970s.Task9.2NetworkArchitectureLearningObjectivesAftercompletingthistask,youshouldbeableto:knowtheOSIreferencemodel;knowtheTCP/IPreferencemodel;explainnetworkarchitecture.LearningPreparationKeyterms—networkarchitecture；OpenSystemInterconnection(OSI);TCP/IPreferencemodel;referencemodel;connectivity;TCP(TransmissionControlProtocol);FTP（FileTransferProtocol);SMTP（SimpleMessageTransferProtocol）Relativespecializedknowledge;InternetPlanandImplementStep1ReadRelativeKnowledge;Step2Requirestudentstograspthekeytermsinthistask;Step3Assessment.InquiryandDiscoveryWhyaretheredifferentnetworkarchitectures?Networkarchitecturedescribeshowacomputernetworkisconfiguredandwhatstrategiesareused.Inthefollowingtwosectionswewilldiscusstwoimportantnetworksarchitectures.1.OpenSystemInterconnectionReferenceModelTheOpenSystemInterconnection(OSI)referencemodel(SeeFigure9-1)describeshowinformationfromasoftwareapplicationinonecomputermovesthroughanetworkmediumtoasoftwareapplicationinanothercomputer.TheOSIisanabstractdescriptionforlayeredcommunicationsandcomputernetworkprotocoldesign.Initsmostbasicform,itdividesnetworkarchitectureintosevenlayerswhich,fromtoptobottom,aretheApplication,Presentation,Session,Transport,Network,DataLink,andPhysicalLayers.ItisthereforeoftenreferredtoastheOSISevenLayerModel.ThefollowinglistdetailsthesevenlayersoftheOSIreferencemodel:Layer7—Application.Networkprocesstoapplication.Layer6—Presentation.Datarepresentationandencryption.Layer5—Session.Establishes,maintains,andcoordinatescommunication.Layer4—Transport.End-to-endconnectionsandreliability.Layer3—Network.Pathdeterminationandlogicaladdressing.Layer2—Datalink.Physicaladdressing.Layer1—Physical.Media,signalandbinarytransmission.2.TCP/IPReferenceModelTheTCP/IPreferencemodel(SeeFigure9-2)andrelatedprotocolsaremaintainedbytheInternetEngineeringTaskForce(IETF).ItevolvedfromARPANET,whichwastheworld’sfirstwideareanetworkandapredecessoroftheInternet.TheTCP/IPreferencemodeldescribesasetofgeneraldesignguidelinesandimplementationsofspecificnetworkingprotocolstoenablecomputerstocommunicateoveranetwork.TCP/IPprovidesend-to-endconnectivityspecifyinghowdatashouldbeformatted,addressed,transmitted,routedandreceivedatthedestination.Protocolsexistforavarietyofdifferenttypesofcommunicationservicesbetweencomputers.TCP/IPlooselydefinesafour-layermodel(RFC1122)asfollows:Application(process-to-process)layer.Thisisthescopewithinwhichapplicationscreateuserdataandcommunicatethisdatatootherprocessesorapplicationsonanotherorthesamehost.Thecommunicationspartnersareoftencalledpeers.ExamplesofapplicationlayerprotocolsincludetheFileTransferProtocol(FTP)andtheSimpleMailTransferProtocol(SMTP).Transport(host-to-host)layer.TheTransportLayerconstitutesthenetworkingregimebetweentwonetworkhosts,eitheronthelocalnetworkoronremotenetworksseparatedbyrouters.TheTransportLayerprovidesauniformnetworkinginterfacethathidestheactualtopology(layout)oftheunderlyingnetworkconnections.Thisiswhereflow-control,error_x0002_correction,andconnectionprotocolsexist,suchasTCP.ThislayerdealswithopeningandmaintainingconnectionsbetweenInternethosts.Internet(internetworking)layer.TheInternetLayerhasthetaskofexchangingdatagramsacrossnetworkboundaries.Itisthereforealsoreferredtoasthelayerthatestablishesinternetworking;indeed,itdefinesandestablishestheInternet.ThislayerdefinestheaddressingandroutingstructuresusedfortheTCP/IPprotocolsuite.InternetProtocol(IP)istheprimaryprotocolintheInternetLayeroftheInternetProtocolSuite.Linklayer.Thislayerdefinesthenetworkingmethodswiththescopeofthelocalnetworklinkonwhichhostscommunicatewithoutinterveningrouters.ThislayerdescribestheprotocolsusedtodescribethelocalnetworktopologyandtheinterfacesneededtoaffecttransmissionofInternetLayerdatagramstonext-neighborhosts.(cf.theOSIDataLinkLayer)Task9.3NetworkTopologyLearningObjectivesAftercompletingthistask,youshouldbeabletoidentifydifferentnetworktopology.LearningPreparationKeyterms—networktopology;busnetwork;starnetwork;ringnetwork;hierarchicalnetwork;linenetwork;fullconnectednetwork;meshnetwork;star-busnetwork;treenetworkRelativespecializedknowledge;InternetPlanandImplementStep1ReadRelativeKnowledge;Step2Requirestudentstograspthekeytermsinthistask;Step3Assessment.InquiryandDiscoveryNetworkTopologyistheschematicdescriptionofanetworkarrangement,connectingvariousnodesthroughlinesofconnection.Canyoulistfeaturesofbusnetwork,starnetwork,ringnetwork,meshnetwork,ortreenetwork?Networktopology(SeeFigure9-3)isthestudyofthearrangementormappingoftheelements(links,nodes,etc.)ofanetwork,especiallythephysical(real)andlogical(virtual)interconnectionsbetweennodes.Thephysicalandlogicaltopologiesmightbeidenticalinanyparticularnetworkbuttheyalsomaybedifferent.Computernetworksmaybeclassifiedaccordingtothenetworktopologyuponwhichthenetworkisbased,suchasbusnetwork,starnetwork,ringnetwork,meshnetwork,star-busnetwork,treeorhierarchicaltopologynetwork.Networktopologysignifiesthewayinwhichdevicesinthenetworkseetheirlogicalrelationstooneanother.Theuseoftheterm“logical”hereissignificant.Thatis,networktopologyisindependentofthe“physical”layoutofthenetwork.Evenifnetworkedcomputersarephysicallyplacedinalineararrangement,iftheyareconnectedviaahub,thenetworkhasastartopology,ratherthanabustopology.Inthisregardthevisualandoperationalcharacteristicsofanetworkaredistinct;thelogicalnetworktopologyisnotnecessarilythesameasthephysicallayout.网络拓扑Task9.4TypesofNetworksLearningObjectivesAftercompletingthistask,youshouldbeabletodescribelocalarea,metropolitanarea,andwideareanetworks.LearningPreparationKeyterms—localareanetwork(LAN);metropolitanareanetwork(MAN);wideareaRelativespecializedknowledge;InternetPlanandImplementStep1ReadRelativeKnowledge;Step2Requirestudentstograspthekeytermsinthistask;Step3Assessment.InquiryandDiscoveryPerformanceofcomputernetworkscanbemeasuredbytransittimeandresponsetime.Canyouexplainthesetwoperformance?Networksmaybecitywideandeveninternational,usingbothcableandairconnections.Belowisalistofthemostcommontypesofcomputernetworksinorderofscale.LocalAreaNetwork(LAN).Alocalareanetworkisacomputernetworkcoveringasmallphysicalarea,likeahome,anoffice,orasmallgroupofbuildings,suchasaschool,oranairport.MetropolitanAreaNetwork(MAN).Ametropolitanareanetworkisanetworkthatconnectstwoormorelocalareanetworksorcampusareanetworkstogetherbutdoesnotextendbeyondtheboundariesoftheimmediatetown/city.Routers,switchesandhubsareconnectedtocreateametropolitanareanetwork.WideAreaNetwork(WAN).Awideareanetworkisacomputernetworkthatcoversabroadarea(i.e.,anynetworkwhosecommunicationslinkacrossmetropolitan,regional,ornationalboundaries).Thelargestandmostwell-knownexampleofaWANistheInternet,whichspanstheentireglobe.ValuesEducationthroughCurriculumScientistSpirit:PromotingtheScientistSpiritandBravelyClimbingtheWorldScienceandTechnologySummit6GtoImproveConnectivityofAllThingsMobilecommunicationhastransformedtheworldinthepastfourdecades,witheachdecadewitnessingtheemergenceofatleastonenewgenerationtechnology.While5Gtechnologyopenedthedoortotheinternetofthings,6Gaimstofurtheradvancethisconceptbyevolvingintoaplatformfor“connectedintelligence”.The6Gtechnologyisexpectedtohelpmobilecommunicationnetworkstoconnectavastarrayofsmartdevices,enablingreal-timeconnectivitybetweenthephysicalanddigitalworldsthroughartificialintelligence(AI)andmachinelearning.Also,itwilllikelyenablepeopletoaccessandretrieveawealthofinformationinrealtime,andhelpthementeranintelligent,interconnectedworld.Assuch,6Gwillusherinthenextwaveofdigitalization.The6Gtechnologywillhelpboostproduction,improvepeople’slifestyle,enhanceefficiency,promoteinnovationintheinformationandcommunicationstechnology(ICT)sector,andcreatenewopportunitiesforthedigitaleconomy.Thetechnology’spotentialapplicationsincludeintegratedair,spaceandgroundcommunication,whichwillallowuserstoseamlesslyaccessmobilebroadbandincities,ruralareas,andevenonairplanesandships.Itisthusclearthat6Gwillhelpempowerindustries,integratevarioussectors,andcreate,forinstance,smartfactories,promoteconnectedvehiclesandboosttelemedicine.ValuesEducationthroughCurriculumChineseinternetcompaniesandequipmentmanufacturershavebeenconductingresearchin6Gbasedontheirrespectivetechnologicaladvantages.Forexample,ChinaMobile,afterproposingtheworld’sfirstsystemic6Gnetworkarchitecture,achievedbreakthroughsinkeytechnologiessuchasnewwirelesstransmission,newnetworkprotocolsanddigitaltwinnetworks.AndmajorequipmentmanufacturerssuchasHuaweiandZTEhaveintensifiedresearchin6G.Forinstance,in2022,Huaweireleasedawhitepaperon6G,whichisacomprehensiveanalysisofthepotentialapps,requirementsandsupportingtechnologiesfor6Gwirelessnetworks.感谢聆听计算机英语（第三版）北京出版社Unit10InternetTask10.1InternetTask10.2InternetProtocolandIPAddressTask10.3CommonUsesTask10.4DomainNameSystem目录01020304directoryTask10.1InternetLearningObjectivesAftercompletingthistask,youshouldbeabletodefinethetermofInternet.LearningPreparationKeyterms—Internet;ARPANETRelativespecializedknowledge;InternetPlanandImplementStep1ReadRelativeKnowledge;Step2Requirestudentstograspthekeytermsinthistask;Step3Assessment.InquiryandDiscoveryTheInternetisaworldwidenetwork,linkingcomputerstocomputers.WhyistheInternetconsideredanetwork?Internet,theworld-widenetworkofcomputernetworks,waslaunchedin1969whentheUnitedStatesfundedaprojectthatdevelopedanationalcomputernetworkcalledARPANET(AdvancedResearchProjectAgencyNetwork).ItisbasedonacommonaddressingsystemandcommunicationsprotocolcalledTCP/IP.TheInternetisaglobalnetworkofinterconnectedcomputers,enablinguserstoshareinformationalongmultiplechannels.Typically,acomputerthatconnectstotheInternetcanaccessinformationfromavastarrayofavailableserversandothercomputersbymovinginformationfromthemtothecomputer’slocalmemory.Thesameconnectionallowsthatcomputertosendinformationtoserversonthenetwork;thatinformationisinturnaccessedandpotentiallymodifiedbyavarietyofotherinterconnectedcomputers.AmajorityofwidelyaccessibleinformationontheInternetconsistsofinter-linkedhypertextdocumentsandotherresourcesoftheWorldWideWeb(WWW).ComputeruserstypicallymanagesentandreceivedinformationwithWebbrowsers;othersoftwareforusers’interfacewithcomputernetworksincludesspecializedprogramsforelectronicmail,onlinechat,filetransferandfilesharing.ThemovementofinformationontheInternetisachievedviaasystemofinterconnectedcomputernetworksthatsharedatabypacketswitchingusingthestandardizedInternetProtocolSuite(TCP/IP).Itisa“networkofnetworks”thatconsistsofmillionsofprivateandpublic,academic,business,andgovernmentnetworksoflocaltoglobalscopethatarelinkedbycopperwires,fiber-opticcables,wirelessconnections,andothertechnologies.Task10.2InternetProtocolandIPAddressLearningObjectivesAftercompletingthistask,youshouldbeableto:definethetermofInternetprotocol;definethetermofIPaddress.LearningPreparationKeyterms—Internetprotocol;IPaddress;InternetserviceproviderRelativespecializedknowledge;InternetPlanandImplementStep1ReadRelativeKnowledge;Step2Requirestudentstograspthekeytermsinthistask;Step3Assessment.InquiryandDiscoveryEveryInternetusermusthavecomeacrossthesetwoterminologies—IPv4andIPv6.What’sthedifferencebetweenIPv4andIPv6?TheInternetProtocol(IP)isaprotocol,orsetofrules,forroutingandaddressingpacketsofdatasothattheycantravelacrossnetworksandarriveatthecorrectdestination.DatatraversingtheInternetisdividedintosmallerpieces,calledpackets.IPinformationisattachedtoeachpacket,andthisinformationhelpsrouterstosendpacketstotherightplace.EverydeviceordomainthatconnectstotheInternetisassignedanIPaddress.AnInternetProtocol(IP)address(SeeFigure10-1)isanumericalidentification(logicaladdress)thatisassignedtodevicesparticipatinginacomputernetworkutilizingtheInternetProtocolforcommunicationbetweenitsnodes.AlthoughIPaddressesarestoredasbinarynumbers,theyareusuallydisplayedinhuman-readablenotations,suchas66(forIPv4),and

2001:db8:0:1234:0:567:1:1(forIPv6).TheroleoftheIPaddresshasbeencharacterizedasfollows:“Anameindicateswhatweseek.Anaddressindicateswhereitis.Arouteindicateshowtogetthere.”TheoriginaldesignersofTCP/IPdefinedanIPaddressasa32-bitnumberandthissystem,nownamedInternetProtocolVersion4(IPv4),isstillinusetoday.However,duetotheenormousgrowthoftheInternetandtheresultingdepletionoftheaddressspace,anewaddressingsystem(IPv6),using128bitsfortheaddress,wasdeveloped.TheInternetAssignedNumbersAuthority(IANA)managestheIPaddressspaceallocationsglobally.IANAworksincooperationwithfiveRegionalInternetRegistries(RIRs)toallocateIPaddressblockstoLocalInternetRegistries(Internetserviceproviders)andotherentities.ValuesEducationthroughCurriculumScientistSpirit:PromotingtheScientistSpiritandBravelyClimbingtheWorldScienceandTechnologySummitNext-genInternetAcceleratesDataFlowChinahaslaunchedtheworld’sfirstultrahigh-speednext-generationinternetbackbone,withatransferrateofbandwidthreaching1,200gigabitspersecond(1.2T),markingamilestoneinglobalinternetinfrastructure,expertssaidatanewsconferenceatTsinghuaUniversityinBeijingonNovember13,2023.Thebackboneisahigh-speeddatatransmissionlinethatcanprovidenetworkfacilitiestointernetserviceproviders.JointlydevelopedbyTsinghuaUniversity,ChinaMobile,HuaweiandTheChinaEducationandResearchNetwork,theultrahigh-speedinternetbackbonecoversmorethan3,000kilometerslinkingBeijing,WuhaninHubeiprovinceandGuangzhouinGuangdongprovince.The1.2Tbackbonenetworkiscapableoftransferring150high-definitionmoviesinjust1second,exhibitingatransmissionefficiencymorethan10timesthatofthecurrent100Gnetwork.It’sbuiltonkeycoretechnologiesdevelopedindependentlyinChina,includingthe1.2Tultrahigh-speedIPv6interfaceinthenext-generationinternetcorerouter.Thebackboneachievescompletedomesticproductionandindependentcontrolofbothsoftwareandhardwarecomponents,positioningitsoveralltechnologicalcapabilityattheforefrontglobally.网络强国

中国行动Task10.3CommonUsesLearningObjectivesAftercompletingthistask,youshouldbeableto:knowhowtoaccesstheInternet;knowhowtosendE-mail;knowhowtousesearchengines,messagingappandmicroblog;knowhowtoremoteaccess.LearningPreparationKeyterms—Internet;E-mail;Cc(carboncopy);Bcc(blindcarboncopy);compose;searchengine;WorldWideWeb;URL;HTTP;interactive;remoteaccess;microblog;messagingappRelativespecializedknowledge;InternetPlanandImplementStep1ReadRelativeKnowledge;Step2Requirestudentstograspthekeytermsinthistask;Step3Assessment.InquiryandDiscoveryTherearemanymessagingAppsuchasQQ,WhatsApp,GoogleMessenger,WeChat,FacebookMessenger.WhichAppwouldyouchooseonAndroid?ThecommonusesoftheInternetinclude:E-mail,theWorldWideWeb,remoteaccess,collaboration,filesharing,streamingmedia,andInternettelephony(VoIP).Now,wemainlydiscussE-mail,theWorldWideWebandremoteaccess.1.E-mailElectronicmail(oftenabbreviatedasE-mailorEmail)isanymethodofcreating,transmitting,orstoringprimarilytext-basedhumancommunicationswithdigitalcommunicationssystems.ModernE-mailsystemsarebasedonastore-and-forwardmodel.ToparticipateinE-mail,apersonmustbeassignedamailbox,whichisinfactastorageareawheremessagescanbeplaced.Eachmailboxhasanaddressintheformofusename@.AnE-mailaddressisastringdividedintotwopartsbythe@character(pronouncedas“at”).Thefirstpartisamailboxidentifier,andthesecondstandsforthenameofthecomputeronwhichthemailboxresides.Mailboxidentifiersareassignedlocally,andonlyhavesignificanceononecomputer.Onsomecomputersystems,themailboxidentifieristhesameasauser’slog-inaccountidentifier;onthesystem,thetwoareindependent.ThecomputernameinanE-mailaddressisadomainname.Onceyou’veloggedintosuchfreeE-mailprovidersasYahooandHotmail,usingyourmailaccount,youcansendE-mailtoanyvalidemailaddress.Clickthecomposelinkonthenavigationbartobegincomposingamessage.InternetE-mailmessagesconsistoftwomajorsections(SeeFigure10-2).(1)Header.Structuredintofieldssuchassummary,sender,receiver,andotherinformationabouttheE-mail.(2)Body.Themessageitselfasunstructuredtext;sometimescontainingasignatureblockattheend.1.1HeaderThemessageheader(SeeFigure10-2)usuallyincludesatleastthefollowingfields:(1)From.TheE-mailaddress,andoptionallythenameofthesender.(2)To.TheE-mailaddress(es),andoptionallyname(s)ofthemessage’srecipient(s).Tosendamessage,youmustalwaysspecifyatleastonerecipientinthe“To:”field.Ifyoudonot,anerrormessagewillappearwhenyouattempttosendthemessage.(3)Subject.Abriefsummaryofthecontentsofthemessage.(4)Date.Thelocaltimeanddatewhenthemessagewaswritten.Anothercommonheader(SeeFigure10-3)includesatleastthefollowingfields:(1)Cc.Standsfor“carboncopy”.Anyonelistedinthe“Cc:”fieldofamessagewillreceiveacopyofthatmessagewhenyousendit.Allotherrecipientsofthatmessagewillbeabletoseethatthepersonyoudesignatedasa“Cc:”recipienthasreceivedacopyofthemessage.(2)Bcc.Standsfor“blindcarboncopy”.Thisissimilartothe“Cc:”feature,exceptthat“Bcc:”recipientsareinvisibletoalloftheotherrecipientsofthemessage(includingother“Bcc:”recipients).Forexample,ifyousendamessageTo:hd@andBcc:myclass@126.,thenhdwillseehimselfasthemessage’sonlyrecipient,whilemyclasswillseethatyouhavealsosentthemessagetohd.Tosendyourmessagetomorethanoneperson,addadditionalemailaddressesinthe“To:”,“Cc:”,and/or“Bcc:”fieldsseparatedbycommas(SeeFigure10-4).Ifyoudonotentervalidemailaddresses,orifyoudonotusecommastoproperlyseparateyourrecipients’addresses,yourmessagewillnotbesent.Instead,youwillseethemessage,“Unfortunately,therewasaproblem:Eitherthereisasyntaxerrorinoneofyouraddressfields,oryouhaveusedanaliaswhichisnotinyourAddressBook.”1.2ReplytoaMessageToreplytoamessagethatyouhavereceivedinyourE-mailaccount,youmustfirstopenthemessageonyourscreen.Whenthemessageisopen(SeeFigure10-2).(1)Clickthe“Reply”buttonatthetopofthemessagewindowtoreplyonlytothesenderofthemessage.Ifyouwouldliketosendyourreplytoalloftheotherrecipientsofthemessageinadditiontothesender,clickthe“ReplyAll”button.(2)AComposeMailwindow(SeeFigure10-3)willappear.Ifyouclickedthe“Reply”button,thesender’semailaddresswillappearinthe“To:”field.Ifyouclickedthe“ReplyAll”button,theninadditiontothesender’saddress,theaddressesofalloftheotherrecipientswillappearinthe“To:”and/or“Cc:”fields,accordingtothewaytheywerelistedintheoriginalmessage.Youcanalsoaddnewemailaddressesifyouwish.(3)Typeyourreply.Ifyouhavequotedthesender’smessage,youcantypeintheareaabovethesender’smessageaswellwithinthesender’smessageitself.(4)Toattachafiletoyourmessage,clicktheBrowsebuttonandselectafile.Whenyou’veselectedafile,clickthe“Attach”linktoattachittoyourmessage.(5)Clickthe“Send”buttontosendyourreply.Pleasenote:Ifyouareinthemiddleofcomposingamessage,it’simportantthatyoueithersendthemessageorclickthe“SaveDraft”buttonbeforeclickinganyofthelinksontheleft-handnavigationbarorviewinganothersite.Ifyoudon’tdothis,yourbrowser’s“Back”buttonmaynotworktoretrievethetextthatyouhavetyped.2.TheWorldWideWebTheWorldWideWebisahugesetofinterlinkeddocuments,imagesandotherresources,linkedbyhyperlinksandURLs.ThesehyperlinksandURLsallowtheWebserversandothermachinesthatstoreoriginals,andcachedcopiesof,theseresourcestodeliverthemasrequiredusingHTTP(HypertextTransferProtocol).HTTP(SeeFigure10-5)isonlyoneofthecommunicationprotocolsusedontheInternet.SoftwareproductsthatcanaccesstheresourcesoftheWebarecorrectlytermeduseragents.Innormaluse,Webbrowsers,suchasInternetExplorer,FirefoxandAppleSafari,accessWebpagesandallowuserstonavigatefromonetoanotherviahyperlinks.Webdocumentsmaycontainalmostanycombinationofcomputerdataincludinggraphics,sounds,text,video,multimediaandinteractivecontentincludinggames,officeapplicationsandscientificdemonstrations.Throughkeyword-drivenInternetresearchusingsearchengines(SeeFigure10-6)likeBaiduandGoogle,millionsofpeopleworldwidehaveeasy,instantaccesstoavastanddiverseamountofonlineinformation.Comparedtoencyclopediasandtraditionallibraries,theWorldWideWebhasenabledasuddenandextremedecentralizationofinformationanddata.UsingtheWeb,anyonecanfindwaystopublishaWebpage,ablogorbuildawebsiteforverylittleinitialcost.AdvertisingonpopularWebpagescanbelucrative,ande-commerceorthesaleofproductsandservicesdirectlyviatheWebcontinuestogrow.3.RemoteAccessTheInternetallowscomputeruserstoconnecttoothercomputersandinformationstoreseasily,wherevertheymaybeacrosstheworld.Theymaydothiswithorwithouttheuseofsecurity,authenticationandencryptiontechnologies,dependingontherequirements.Thisisencouragingnewwaysofworkingfromhome,collaborationandinformationsharinginmanyindustries.Anaccountantsittingathomecanauditthebooksofacompanybasedinanothercountry,onaserversituatedinathirdcountrythatisremotelymaintainedbyITspecialistsinafourth.Theseaccountscouldhavebeencreatedbyhome-workingbookkeepers,inotherremotelocations,basedoninformationE-mailedtothemfromofficesallovertheworld.SomeofthesethingswerepossiblebeforethewidespreaduseoftheInternet,butthecostofprivateleasedlineswouldhavemademanyoftheminfeasibleinpractice.Anofficeworkerawayfromhisdesk,perhapsontheothersideoftheworldonabusinesstriporaholiday,canopenaremotedesktopsessionintohisnormalofficePCusingasecureVirtualPrivateNetwork(VPN)connectionviatheInternet.Thisgivestheworkercompleteaccesstoallofhisorhernormalfilesanddata,includingE-mailandotherapplications,whileawayfromtheoffice.4.MicroblogMicroblog(SeeFigure10-7)isabroadcastmediumintheformofblog.Aswithtraditionalblog,microbloggerspostabouttopicsrangingfromthesimple,suchas“whatI’mdoingrightnow,”totheFigure10-7MicroblogofSinathematic.Microblogdiffersfromatraditionalbloginthatitscontentistypicallysmallerinbothactualandaggregatefilesize.Microblog“allowuserstoexchangesmallelementsofcontentsuchasshortsentences,individualimages,orvideolinks”.Basedonuserinformationsharing,communicationandaccessplatform,theuserscanbuildtheirowncommunitythroughtheWEB,WAPandotherclients,theycanalsoupdateinformationabout140wordstorealizethesharing.Somemicroblogservicesofferfeaturessuchasprivacysettings,whichallowuserstocontrolwhocanreadtheirmicroblog,oralternativewaysofpublishingentriesbesidestheweb_x0002_basedinterface.Thesemayincludetextmessaging,instantmessaging,E-mail,digitalaudioordigitalvideo.ThetwitteroftheUnitedStatesistheearliestandm