计算机网络专业英语 课件 Lesson 4 Examples of Network Application.pptx
L4-1
Lesson4ExamplesofNetworkApplicationText1E-mail
要点KeyPoints：SMTP/POP/IMAP邮件系统的工作过程HostPersonal/professional提高/减少/提升Message/informationConnection/link
E-mail(Electronic-mail)isatechnologythatincludespassingandsendinginformationfromoneplacetoanother,usingacomputerandtheInternet.Ithasprovenbeneficialinourpersonalaswellasprofessionallife.AmajorityofbusinessesaroundtheglobeuseE-mailasthemostemployedmethodofrapidandeffectiveofficecommunication.Itisanimportanttoolforcorporatecommunication.FromthetimeE-mailhasbeenusedasacommunicationtool,businesseshaveexperiencedarapidriseinproductivityandreductioninexpenses,andfoundnewwaystoimprovetheirservices.TheadvantagesofE-mailcommunicationcanbeseeninlarge-scaleaswellassmall-scaleindustriesandorganizations.However,theadvantagesarenotlimitedonlytothebusinessworld.WealsouseE-mailsinourday-to-daylivesforsendingandreceivingmessagesfromourfriendsandfamilymembers.send发送→pass传递→receive接收/accept接受确认、承认access存、取/retrieve检索、恢复、取回retrievalPut/push推送/get获取request请求/respond响应/reply回复pass传递，deliver投递、交付，distribute分散personal个人的和professional职业的Officecorporateprivate私有的和public公有的Responsibility责任Information信息Message消息
ByusingTCP,SMTP(SimpleMailTransferProtocol)sendsE-mailtoothercomputersthatsupporttheTCP/IPprotocolsuite.SMTPprovidesextensiontothelocalmailservicesthatexistedintheearlyyearsofLANs.ItsupervisestheE-mailsendingfromthelocalmailhosttoaremotemailhost.Itisnotreliableforacceptingmailfromlocalusersordistributingreceivedmailtorecipients.Thisistheresponsibilityofthelocalmailsystem.SMTPmakesuseofTCPtoestablishaconnectiontotheremotemailhost,themailissent,anywaitingmailisrequestedandthentheconnectionisdisconnected.Itcanalsoreturnaforwardingaddressiftheintendedrecipientnolong