通信及基础工程26

Unit3TextAInternet&CommunicationInternet&Communication1.WhatisinternetTheinternet

hasrevolutionizedthewayweworkandplay.Itallowsustocommunicate,tosharedataandtoseekinformationinamatterofseconds.Allthisispossiblethroughtheuseofcomputersandnetworks.TextTextWordsNotesDiscussionHomeTheinternetisaglobalnetworkofcomputers.Allcomputerdevices(includingPCs,laptops,gamesconsolesandsmartphones)thatareconnectedtotheinternetformpartofthisnetwork.Addedtogether,therearebillionsofcomputersconnectedtotheinternet,allabletocommunicatewitheachother.Today,theinternetisamassivepartofourdailylives.TextTextWordsNotesDiscussionHomeTextTextWordsNotesDiscussionHome2.Howdidtheinternetoriginate?Inthe1950s,theUnitedStatesDefenceDepartmentformedseveralagencies,suchastheAdvancedResearchProjectsAgency(ARPA,nowknownasDARPA)withthepurposeofdevelopingtechnology.However,sincetheywerebasedatuniversitiesaroundthecountry,ARPA’sscientistscouldnoteasilycommunicateorshareinformation.Tosolvethisproblem,ARPAcreatedanetworkofcomputers,whichtheycalledARPANET.RealizinghowusefulARPANETwas,otherorganizationsbuilttheirownnetworks.However,theseindividualnetworkscouldnoteasilycommunicatewitheachother.TextTextWordsNotesDiscussionHomeInthe1970s,aprotocolwasdeveloped.CalledTCP/IP,thisprotocolallowedtheseparatenetworkstocommunicatewitheachother.Thejoiningoftheseindividualnetworkscreatedahugewideareanetwork(WAN)whichcametobeknownastheinternet.TextTextWordsNotesDiscussionHomeSincethentheuseoftheinternetbyorganizationsandindividualshasgrownyearuponyear.Inthebeginning,ARPANETconsistedofjustfourcomputers.Nowbillionsofcomputersareconnectedtotheinternet.Whenweconnecttotheinternet,wearesaidtobe‘online’.Todaytheinternethasmanyonlinefacilities,forexample:TextTextWordsNotesDiscussionHome—communicationviaemailandVoIP—sharingofinformationsuchastext,images,soundsandvideos—storageofinformation—streamingtelevisionprogrammes,films,videos,soundsandmusic—playingonlinegames—shopping—socialnetworking—bankingTextTextWordsNotesDiscussionHomeMostoftheseonlinefacilitiesareavailablethroughtheuseofwebsitesontheWorldWideWeb.TextTextWordsNotesDiscussionHome3.WhatisWorldWideWeb?Theinternetisaglobalnetworkofcomputers.TheWorldWideWebisthepartoftheinternetthatcanbeaccessedthroughwebsites.Websitesconsistofwebpages

whichallowyoutoseeinformation.TextTextWordsNotesDiscussionHomeWebsitesareaccessedusingawebbrowser.Abrowserisaprogramdesignedtodisplaytheinformationheldonawebsite.Everywebsitehasanaddressatwhichitcanbefound,abitlikeahouseaddress.TextTextWordsNotesDiscussionHomeAwebsite’saddressisknownasitsURL.AwebsitecanbevisitedbytypingitsURLintoawebbrowser.Eachaddresscontainstheprefix‘http:’whichtellsthecomputertousethehypertexttransferprotocol

forcommunicatingwiththewebsite.[1]Thebrowserthenconnectstotheinternet,findsthewebsiteatitsaddressanddownloads

theinformationstoredthereontoourcomputerforustoview.Websitesandwebpagesarejoinedtogetherusinghyperlinks.Clickingonahyperlinktakesustoanothersiteorpage.TextTextWordsNotesDiscussionHome4.TransferringinformationviatheinternetTheinternetisaglobalnetworkofcomputers,someofwhicharecalledwebservers.Awebserverisacomputerwhichholdswebsitesforothercomputerslinkedtotheinternettoaccess.Holdingawebsiteisknownas‘hosting’.Awebservermayhostoneormanywebsitesandwebpages.Sendinginformationtoawebserverisknownasuploading.Receivinginformationfromawebserverisknownasdownloading.TextTextWordsNotesDiscussionHomeWhenyoumakeatelephonecall,adirectconnectionisformedbetweenyouandthepersonyouarecalling.Whileyouaremakingthecall,nooneelsecancommunicatewithyou.Awebserverneedstobeabletocommunicatewithmanydifferentcomputersatthesametime.Wheninformationisuploadedto,ordownloadedfrom,awebserveritisbrokenupintotinypiecescalleddatapackets.Eachpacketisaveryshortcommunicationbetweentheclientcomputerandthewebserver.Becauseeachcommunicationlastsonlymilliseconds,thewebservercanseeminglycommunicatewithmanycomputersatthesametime.Itisabitlikehavingseveralconversationsatthesametime,butonlysayingonewordtoeachpersoninturn.TextTextWordsNotesDiscussionHome5.UsingHTMLtocreatewebsiteAllwebpagesontheinternetarecreatedusingalanguagecalledHypertextMarkupLanguage

(HTML)[2].

HTMLdescribes:—whatinformationappearsonawebpage—howitappearsonthepage(formatting)—anylinkstootherpagesorsites TextTextWordsNotesDiscussionHomeHTMLcanbewritteninspecialistsoftware,orinasimpletexteditorlikeNotepad.Aslongasthedocumentissavedwiththefileextension

‘.html’itcanbeopenedandviewedasawebpagefromabrowser.ThisexampleHTMLcodedisplaysamessageonawebpage:TextTextWordsNotesDiscussionHome<html> <body> <h1>Helloworld</h1> <p>Thisismyfirstwebpage</p> </body></html>TextTextWordsNotesDiscussionHomeThecodeusestagstodescribetheappearanceoftheinformation:—<html>statesthatthedocumentisaHTMLdocument—<body>statesthattheinformationappearsinthebodyofthepage—<h1>statesthatthefollowingtextappearsasaprominentheading—<p>statesthatthisisthebeginningofanewparagraphTextTextWordsNotesDiscussionHomeTextTextWordsNotesDiscussionHome6.UsingemailtocommunicateTwoofthemainwaysinwhichpeopleusetheinternetforcommunicationareemailandVoIP[3].Email(shortforelectronicmail)isthedigitalequivalentofsendingaletter.Eachemailhasasender,areceiverandamessage.Thebigdifferenceisthatinsteadofwaitingforourpostedlettertobedeliveredbythepostoffice,anemailissentandreceivedalmostimmediately.TextTextWordsNotesDiscussionHomeTextTextWordsNotesDiscussionHomeAdvantagesanddisadvantagesofemailAsidefromspeed,emailhasseveralotheradvantages:—Itcostsvirtuallynothingtosendanemail,whereasyouneedtobuystampstopostaletter.—Thesameemailcanbesenttomanypeopleatthesametime.—Assets,suchastext,videosorsoundclips,canbeattachedtoemail.—Arecordiskeptofeachsentemail,soitispossibletoreferbacktocheckwhatwassent.TextTextWordsNotesDiscussionHome—Whenemailsaresent,therecipientdoesn’thavetobethere.Emailscanbesentlateatnightandtherecipientwillseeitwhentheychecktheiremailthefollowingday.Thishasgreatbenefitswhensendingemailstoanotherpartoftheworld.—Emailscanbesentatanytimeordayoftheyear.PostisnotusuallydeliveredonSundaysorbankholidays.—Emailscanbesentandreceivedonvariousinternetconnecteddevices,egPCs,laptops,gamesconsoles,tabletsorsmartphones.—Emailscanbeautomaticallyforwardedontoanotheraddress.TextTextWordsNotesDiscussionHomeUsingemailhasitsdisadvantagestoo:—Therecipientcanonlyreceivetheemailiftheyareconnectedtotheinternet.—Emailscansometimescontainvirusesintheformofattachments.—Spamemailscanbeaproblem.Socanphishingemails,whicharedesignedtotrickpeopleintogivingawaypersonalinformation.—Becauseemailscanbedeliveredtointernet-connecteddigitaldevicesanywhere,theycanbehardtogetawayfrom.TextTextWordsNotesDiscussionHome7.UsingVoIPandvideoconferencingAvideoconferenceislivevideostreamedovertheinternetsothatpeoplecancommunicatefacetofacewithoutbeinginthesameroom.Althoughthiswasmainlyusedbybusinessesandacademicsatfirst,videoconferencingisnowusedsociallybymanypeople.VoiceoverInternetProtocol(VoIP)isthetechnologythatallowsustovideoconference.ManycompaniesofferfreeVoIPservices,includingSkype,AppleFacetimeandGoogleHangouts.TextTextWordsNotesDiscussionHomeTovideoconferencewithanotherperson,bothpeopleneedaninternet-connectedcomputerwithamonitor,webcam,microphoneandspeakers.Thewebcamallowsvideoimagestobesent,whichareseenonthemonitor,andthemicrophoneallowssoundtobetransmitted,whichisheardthroughspeakers.AprogramcalledaVoIP

clienthandlesthecommunication.TextTextWordsNotesDiscussionHomeVideoconferencingtechnologyisbuiltintomanymodernlaptops,tabletsandsmartphones,andVoIPappsareavailabletouse,oftenforfree.TextTextWordsNotesDiscussionHomeAdvantagesanddisadvantagesofvideoconferencingVideoconferencinghasseveraladvantages:—Seeingaswellashearingtheotherperson.—Showingotherswhatisgoingonaroundus.—Reducingtimetotraveltoseeandspeakwithsomeone.Thishasevengreaterbenefitsiftheotherpersonisontheothersideoftheworld.—Savingmoney,intravelcosts.—Theabilitytovideoconferenceseveralpeopleindifferentlocations,atthesametime.TextTextWordsNotesDiscussionHomeUsingvideoconferencingalsohasitsdisadvantages:—Everyonewhowantstovideoconferencemusthavesuitablehardwareandsoftware.—Videoconferencingfromsmartphonescanbeexpensivebecauseofthehighdatausage.—Streamingvideotwowaysrequiresagooddealofbandwidth.Youmightstruggletovideoconferenceifyourconnectiontotheinternetisofpoorquality.FromBBCTextTextWordsNotesDiscussionHomelaptopn.便携式电脑consolen.控制台，操纵台；演奏台smartphonen.智能手机massiveadj.大量的，重的，大块的hyperlinkn.超链接uploadv.上传WordsWordsTextWordsNotesDiscussionHomemillisecondn.毫秒extensionn.伸展，扩大；电话分机virtuallyadv.几乎；实际上phishv.网络钓鱼monitorn.监视器；显示屏recipientn.接受者；容器，容纳者WordsTextWordsNotesDiscussionHomewebcamn.网络摄像头clientn.[经]客户；顾客；委托人WordsTextWordsNotesDiscussionHome[1]Eachaddresscontainstheprefix‘http:’whichtellsthecomputertousethehypertexttransferprotocolforcommunicatingwiththewebsite.hypertexttransferprotocol是互联网上应用最为广泛的一种网络协议。所有的WWW文件都必须遵守这个标准。设计HTTP最初的目的是为了提供一种发布和接收HTML页面的方法。1960年美国人TedNelson构思了一种通过计算机处理文本信息的方法，并称之为超文本（hypertext）,这成为了HTTP超文本传输协议标准架构的发展根基。TedNelson组织协调万维网协会（WorldWideWebConsortium）和互联网工程工作小组（InternetEngineeringTaskForce）共同合作研究，最终发布了一系列的RFC，其中著名的RFC2616定义了HTTP1.1。TextWordsNotesDiscussionNotesHome[2]HypertextMarkupLanguage即超文本标记语言（缩写：HTML）是为网页创建和其它可在网页浏览器中看到的信息设计的一种标记语言。extensibleHypertextMarkupLanguage即可扩展超文本标记语言（缩写XHTML）是一种新兴的网页设计和制作语言。XHTML是在HTML基础上发展起来的，同时吸取了可扩展标记语言（extensibleMarkupLanguage，XML)的语法严谨的优点。因此，XHTML比HTML具加更加严谨的语法，能够为众多品牌的Web浏览器研发提供规范的技术标准，XHTML的可扩展性和灵活性将适应未来网络应用的更多需求。TextWordsNotesDiscussionHome[3]VoIP（VoiceoverInternetProtocol）简而言之就是将模拟信号（Voice）数字化，以数据封包（DataPacket）的形式在IP网络(IPNetwork）上做实时传递。VoIP最大的优势是能广泛地采用Internet和全球IP互连的环境，提供比传统业务更多、更好的服务。VoIP可以在IP网络上便宜的传送语音、传真、视频、和数据等业务，如统一消息业务、虚拟电话、虚拟语音/传真邮箱、查号业务、Internet呼叫中心、Internet呼叫管理、电话视频会议、电子商务、传真存储转发和各种信息的存储转发等。TextWordsNotesDiscussionHomeQuestionsfordiscussion1.WhatkindofonlineconveniencescanweenjoythroughuseofwebsitesontheWorldWideWeb?2.CanyoulistsomedisadvantagesofEmails?Whatarethey?3.Whataremajoradvantagesofvideoconferencing?4.InwhataspectsdoyouthinkInternetwillfurtherinfluenceus?TextWordsNotesDiscussionHomeAnswerstoquestionsfordiscussionTextWordsNotesDiscussionHome1.WhatkindofonlineconveniencescanweenjoythroughuseofwebsitesontheWorldWideWeb?NowadayswecanenjoyalargequantityofonlineconveniencesbyusingwebsitesontheWorldWideWeb,whichinclude:—communicationviaemailandVoIP—sharingofinformationsuchastext,images,soundsandvideos—storageof