通信及基础工程32

Unit3TextBTypesofInternetCommunicationsTypesofInternetCommunicationsIfyouusetheInternet,thenyouprobablyuseInternet-basedcommunicationstocontactfamily,friendsorco-workers.Fromsendinganinstantmessage[1]toafriend,toe-mailingco-workers,toplacingphonecalls,toconductingvideoconferences,theInternetoffersanumberofwaystocommunicate.TextTextWordsNotesDiscussionHomeTheadvantagesofInternet-basedcommunicationsaremany.Sinceyou'realreadypayingforanInternetaccount(oryouremployeris),youcansavemoneyonphonecallsbysendingsomeoneaninstantmessageorbyusingVoIPinsteadofstandardlocaltelephoneservices.Ofcourse,notechnologyiswithoutadownsideandInternet-basedcommunicationshasplenty,suchasviruses,privacyissuesandspam.TextTextWordsNotesDiscussionHomeLikealltechnologies(andespeciallytechnologytiedtotheInternet),thewaywecancommunicateonlineisconstantlyevolving.Inthisweek's"DidYouKnow...?"articlewe'lltakealookatsomeofthemostpopularformsofInternet-basedcommunications.TextTextWordsNotesDiscussionHome1.InstantMessagingOneofthefastest-growingformsofInternetcommunicationsisinstantmessaging,orIM.ThinkofIMasatext-basedcomputerconferencebetweentwoormorepeople.AnIMcommunicationsserviceenablesyoutocreateakindofprivatechatroomwithanotherindividualinordertocommunicateinreal-timeovertheInternet.Typically,theIMsystemalertsyouwheneversomebodyonyourbuddyorcontactlistisonline.Youcantheninitiateachatsessionwiththatparticularindividual.TextTextWordsNotesDiscussionHomeOnereasonthatIMhasbecomesopopularisitsreal-timenature.Unlikee-mail,whereyouwillwaitfortherecipienttocheckhisorhere-mailandsendareply,ifapersonyouwanttoreachisonlineandavailableinyourIMcontactlist,yourmessageappearsinstantlyinawindowontheirscreen.TextTextWordsNotesDiscussionHomeWhileIMisusedbymillionsofInternetuserstocontactfamilyandfriends,it'salsogrowinginpopularityinthebusinessworld.Employeesofacompanycanhaveinstantaccesstomanagersandco-workersindifferentofficesandcaneliminatetheneedtoplacephonecallswheninformationisrequiredimmediately.Overall,IMcansavetimeforemployeesandhelpdecreasetheamountofmoneyabusinessspendsoncommunications.TextTextWordsNotesDiscussionHomeSomeproblemsandissuesassociatedwithIMincludespimandviruspropagation.SpimistheIMequivalentofspamandisperpetuatedbybotsthatharvestIMscreennamesoffoftheInternetandsimulateahumanuserbysendingspimtothescreennamesviaaninstantmessage.ThespimtypicallycontainsalinktoaWebsitethatthespimmeristryingtomarket.SpimisabitmoreintrusivethanspamduetothenatureofIMitself.Theseadvertisementsandjunkmessageswillpop-upinyourIMwindowandyouneedtodealwiththemessagesimmediately,wherewithe-mailyoucanusuallyfilteralotofitoutanddealwithitlater.(Tobecontinued)TextTextWordsNotesDiscussionHome(Continued)Additionally,virusesandTrojanscanbespreadthroughIMchannels.ThesemaliciousprogramsareusuallyspreadwhenanIMuserreceivesamessagethatlinkstoaWebsitewherethemaliciouscodeisdownloaded.ThemessagewillappeartobefromaknownIMcontact,whichiswhyrecipientsremorelikelytoclickthehyperlinkanddownloadthefile.Usingsafechatrules(suchasneverclickingthelink)andkeepinganupdatedanti-virusprogramonyoursystemwillhelpreducethechancesofbecominginfectedbymaliciousprogramsbeingspreadthroughinstantmessaging.TextTextWordsNotesDiscussionHome2.InternetTelephone&VoIPInternettelephonyconsistsofacombinationofhardwareandsoftwarethatenablesyoutousetheInternetasthetransmissionmediumfortelephonecalls.Foruserswhohavefree,orfixed-priceInternetaccess,Internettelephonysoftwareessentiallyprovidesfreetelephonecallsanywhereintheworld.Initssimplestform,PC-to-PCInternettelephonycanbeaseasyashookingupamicrophonetoyourcomputerandsendingyourvoicethroughacablemodemtoapersonwhohasInternettelephonysoftwarethatiscompatiblewithyours.ThisbasicformofInternettelephonyisnotwithoutitsproblems,however.Connectingthiswayisslowerthanusingatraditionaltelephone,andthequalityofthevoicetransmissionsisalsonotnearthequalityyouwouldgetwhenplacingaregularphonecall.TextTextWordsNotesDiscussionHomeVoIP

isanotherInternet-basedcommunicationsmethodwhichisgrowinginpopularity.VoIPhardwareandsoftwareworktogethertousetheInternettotransmittelephonecallsbysendingvoicedatainpacketsusingIPratherthanbytraditionalcircuittransmissions,calledPSTN(PublicSwitchedTelephoneNetwork).ThevoicetrafficisconvertedintodatapacketsthenroutedovertheInternet,oranyIPnetwork,justasnormaldatapacketswouldbetransmitted.Whenthedatapacketsreachtheirdestination,theyareconvertedbacktovoicedataagainfortherecipient.TextTextWordsNotesDiscussionHomeMuchlikefindinganInternetserviceprovider(ISP)foryourInternetconnection,youwillneedtouseaVoIPprovider.SomeserviceprovidersmayofferplansthatincludefreecallstoothersubscribersontheirnetworkandchargeflatratesforotherVoIPcallsbasedonafixednumberofcallingminutes.YoumostlikelywillpayadditionalfeeswhenyoucalllongdistanceusingVoIP.Whilethissoundsalotlikeregulartelephoneservice,itislessexpensivethantraditionalvoicecommunications,startingwiththefactthatyouwillnolongerneedtopayforextrasonyourmonthlyphonebill.TextTextWordsNotesDiscussionHome3.E-mailShortforelectronicmail,e-mailisthetransmissionofmessagesovercommunicationsnetworks.Themessagescanbenotesenteredfromthekeyboardorelectronicfilesstoredondisk.Mostmainframes,minicomputersandcomputernetworkshaveane-mailsystem.Somee-mailsystemsareconfinedtoasinglecomputersystemornetwork,butothershavegatewaystoothercomputersystems,enablingyoutosendelectronicmailanywhereintheworld.TextTextWordsNotesDiscussionHomeUsingane-mailclient(softwaresuchasMicrosoftOutlookorEudora),youcancomposeane-mailmessageandsendittoanotherpersonanywhere,aslongasyouknowtherecipiente-mailaddress.AllonlineservicesandInternetServiceProviders(ISPs)offere-mail,andsupportgatewayssothatyoucanexchangee-mailwithusersofothersystems.Usually,ittakesonlyafewsecondsforane-mailtoarriveatitsdestination.Thisisaparticularlyeffectivewaytocommunicatewithagroupbecauseyoucanbroadcastamessageordocumenttoeveryoneinthegroupatonce.TextTextWordsNotesDiscussionHomeOneofthebiggestblackcloudshangingovere-mailisspam.Thoughdefinitionsvary,spamcanbeconsideredanyelectronicjunkmail(generallye-mailadvertisingforsomeproduct)thatissentouttothousands,ifnotmillions,ofpeople.Oftenspamperpetratesthespreadofe-mailTrojansandviruses.Forthisreason,it'simportanttouseanupdatedanti-virusprogram,whichwillscanyourincomingandoutgoinge-mailforviruses.TextTextWordsNotesDiscussionHome4.IRCShortforInternetRelayChat,IRCisamulti-userchatsystemthatallowstopeoplegatheron“channels”or“rooms”totalkingroupsorprivately.IRCisbasedonaclient/servermodel.Thatis,tojoinanIRCdiscussion,youneedanIRCclient(suchamIRC)andInternetaccess.TheIRCclientisaprogramthatrunsonyourcomputerandsendsandreceivesmessagestoandfromanIRCserver.TheIRCserver,inturn,isresponsibleformakingsurethatallmessagesarebroadcasttoeveryoneparticipatinginadiscussion.Therecanbemanydiscussionsgoingonatonceandeachoneisassignedauniquechannel.(Tobecontinued)TextTextWordsNotesDiscussionHome(Continued)OnceyouhavejoinedanIRCchatroom(chatroomdiscussionsaredesignatedbytopics),youcantypeyourmessagesinthepublicchatroomwhereallparticipantswillseeit,oryoucansendaprivatemessagetoasingleparticipant.WithmanyIRCclientsyoucaneasilycreateyourownchatroomandinviteotherstojoinyourchannel.Youcanalsopasswordprotectyourchatroomtoallowforamoreprivatediscussionwithjustpeoplewhomyouinvite.TextTextWordsNotesDiscussionHome5.Video-conferencingVideoconferencingisaconferencebetweentwoormoreparticipantsatdifferentsitesbyusingcomputernetworkstotransmitaudioandvideodata.Eachparticipanthasavideocamera,microphoneandspeakersconnectedonhisorhercomputer.Asthetwoparticipantsspeaktooneanother,theirvoicesarecarriedoverthenetworkanddeliveredtotheother'sspeakers,andwhateverimagesappearinfrontofthevideocameraappearinawindowontheotherparticipant'smonitor.TextTextWordsNotesDiscussionHomeInorderforvideoconferencingtowork,theconferenceparticipantsmustusethesameclientorcompatiblesoftware.Manyfreewareandsharewarevideoconferencingtoolsareavailableonlinefordownload,andmostWebcamerasalsocomebundledwithvideoconferencingsoftware.ManynewervideoconferencingpackagescanalsobeintegratedwithpublicIMclientsformultipointconferencingandcollaboration.Inrecentyears,videoconferencinghasbecomeapopularformofdistancecommunicationinclassrooms,allowingforacostefficientwaytoprovidedistancelearning,guestspeakers,andmulti-schoolcollaborationprojects.ManyfeelthatvideoconferencingprovidesavisualconnectionandinteractionthatcannotbeachievedwithstandardIMore-mailcommunications.TextTextWordsNotesDiscussionHome6.SMS&WirelessCommunicationsShortmessageservice(SMS)isaglobalwirelessservicethatenablesthetransmissionofalphanumericmessagesbetweenmobilesubscribersandexternalsystemssuchase-mail,pagingandvoice-mailsystems.Messagescanbenolongerthan160alpha-numericcharactersandmustcontainnoimagesorgraphics.Onceamessageissent,itisreceivedbyaShortMessageServiceCenter(SMSC),whichmustthengetittotheappropriatemobiledeviceorsystem.Aswirelessservicesevolved,MultimediaMessagingService(MMS)wasintroducedandprovidedawaytosendmessagescomprisingacombinationoftext,sounds,imagesandvideotoMMScapablehandsets.TextTextWordsNotesDiscussionHomeCommunicationonwirelessdevicessuchasmobilephonesandPDAsisfrequentlychanging.Todayyoucanuseyourwirelessdevicetonotonlymakephonecalls,buttosendandreceivee-mailandIM.Whileyoucanusee-mail,IRCorIMforfreeifyouhaveanInternetaccount,youwillenduppayingfeestoyourmobilecarriertousetheseservicesonawirelessdevice.TextTextWordsNotesDiscussionHomevirusn.[病毒]病毒；恶毒；毒害spamv.刷屏evolvev.发展，进展；进化；逐步形成initiatevt.开始，创始；使初步了解propagationn.传播；繁殖；增殖perpetuatevt.&adj.使不朽；长存的WordsWordsTextWordsNotesDiscussionHomeintrusiveadj.侵入的；打扰的maliciousadj.恶意的；恶毒的；蓄意的；怀恨的mainframen.[计]主机；大型机videoconferencen.可视会议compatibleadj.兼容的；能共处的；可并立的freewaren.免费软件；自由软件WordsTextWordsNotesDiscussionHomesharewaren.共享软件（等于freeware）collaborationn.合作；勾结；通敌alphanumericadj.

[计]字母数字的WordsTextWordsNotesDiscussionHome[1]instantmessaging（IM）是一种可以让使用者在网络上建立某种私人聊天室（chatroom）的实时通讯服务。目前在互联网上受欢迎的即时通讯软件包括腾讯QQ、微信等。TextWordsNotes