Unit7ComputerCommunications第七单元：计算机通信Telecommunicationsallowspeoplearoundtheworldtocontactoneanother,toaccessinformationinstantly,andtocommunicatefromremoteareas.Telecommunicationsusuallyinvolvesasenderofinformationandoneormorerecipientslinkedbyatechnology,suchasatelephonesystem,thattransmitsinformationfromoneplacetoanother.Telecommunicationsdevicesconvertsdifferenttypesofinformation,suchassoundandvideo,intoelectronicsignals.Thesignalscanthenbetransmittedbymeansofmediasuchastelephonewiresorradiowaves.电信使世界各地的人们得以互相联系，即刻获取信息，并从边远地区实施通信。电信通常涉及一个信息发送者和一个或多个接收者，他们通过电话系统等把信息从一地发送到另一地的技术相联系。电信设备将不同类型的信息，如声音和图像，转换成电子信号。然后，这些信号就可以通过电话线或无线电波等媒介进行发送。Whenasignalreachesitsdestination,thedeviceonthereceivingendconvertstheelectronicsignalbackintoanunderstandablemessage,suchassoundoveratelephone,movingimagesonatelevision,orwordsandpicturesonacomputerscreen.Telecommunicationsenablepeopletosendandreceivepersonalmessagesacrosstown,betweencountries,andtoandfromouterspace.Italsoprovidesthekeymediumfornews,data,information,andentertainment.信号到达目的地后，接收端的设备将电子信号转换回可以理解的信息，如电话中的声音、电视上的活动图像或计算机屏幕上的文字和图片。电信使人们能够在城镇不同地方、国家之间以及向外层空间和从外层空间发送和接收个人信息。电信也为新闻、数据、信息和娱乐提供了关键的媒介。Telecommunicationsmessagescanbesentinavarietyofwaysandbyawiderangeofdevices.Themessagescanbesentfromonesendertoasinglereceiver(point-to-point)orfromonesendertomanyreceivers(point-to-multipoint).Personalcommunications,suchasatelephoneconversationbetweentwopeopleorafacsimile(fax)message,usuallyinvolvepoint-to-pointtransmission.Point-to-multipointtelecommunicationsoftencalledbroadcasts,providethebasisforcommercialradioandtelevisionprogramming.电信信息可通过各种方式和设备发送。信息可由一个发送者发送给一个接收者（点对点），或者由一个发送者发送给多个接收者（点对多点）。个人通信，如两个人之间的电话对话或传真信息，通常涉及点对点的传输。通常称为广播的点对多点电信传输，为商业无线电和电视节目播送提供了基础。Telecommunicationsbeginwithmessagesthatareconvertedintoelectronicsignals.Thesignalsarethensentoveramediumtoareceiver,wheretheyaredecodedbackintoaformthatthepersonreceivingthemessagecanunderstand.Therearevarietyofwaystocreateanddecodesignals,andmanydifferentwaysto