第十四章Computer-Networks.ppt

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,*,*,Section 14.1:Data Communication（,数据通信）,Guidance for your studying:,Keywords:find their definition and understand their meaning.,Carefully read Fig.14-1 and comprehend it.,Write a composition to describe the procession of data communication according to,Fig.14-1.,(homework),Keywords definitions and usages,host,(1)A,computer system,that is accessed by a,user,working at a,remote,location.Typically,the term is used when there are two computer systems connected by,modems,and telephone lines.The,system,that contains the,data,is called the,host,while the,computer,at which the user sits is called the remote,terminal,.,Keywords definitions and usages,Short for,Data Terminal Equipment,a,device,that controls data flowing to or from a computer.The term is most often used in reference to,serial communications,defined by the,RS-232C standard,.This standard defines the two ends of the communications channel as being a DTE and,Data Communications Equipment(DCE),device.In practical terms,the DCE is usually a,modem,and the DTE is the computer itself,or more precisely,the computers,UART chip,.For internal modems,the DCE and DTE are part of the same,device.,DTE,Keywords definitions and usages,Pronounced,u-art,and short for,u,niversal,a,synchronous,r,eceiver-,t,ransmitter,the UART is a,computer,component that handles,asynchronous serial,communication.Every computer contains a UART to manage the,serial ports,and some,internal modems,have their own UART.,UART,USART,short for,Universal Synchronous Asynchronous Receiver/Transmitter,(,IC,),Keywords definitions and usages,Short for,D,ata,C,ommunications,E,quipment,a device that communicates with a,Data Terminal Equipment(DTE),device in,RS-232C,communications.See,DTE,for more information.,DCE,modem,An electronic device that converts,electronic signals,into,sound waves,and sound waves into electronic signals,used to,transmit information,between computers by the use of ordinary telephone lines;also called,modulator-demodulator,;as,the latest modems can transmit data at,56,000 baud,over a clear telephone line.The speed of transmission of information by a modem is usually measured in units of baud,equivalent to bits per second.,Keywords definitions and usages,Pulse Code Modulation-(,PCM),A method by which an,audio signal,is represented as,digital data,.,A technique for,converting,analog signals into digital form.,Virtually all digital audio systems use PCM,including,CD,DAT,F1 format,1630 format,DASH,DCC,and MD.,PCM,Fig.14-1:Simplified block diagram of a data communications link,Peripherals,Host CPU,DTE,DCE,Modem,PCM,coder,PCM,decoder,DCE,Modem,DTE,Keyboard/display,ROP,Parallel digital data,Serial digital data,Transmission media:Microwave,Twisted Pair or coaxial cable,Digital,T-carrier(cable),Secondary CPU,Terminal equipments,数据通信链路简化框图,How to comprehend or interpret this figure?,Fig.14-1:Simplified block diagram of a data communications link,Parallel digital data,Serial digital data,Transmission media:Microwave,Twisted Pair or coaxial cable,Digital,T-carrier(cable),Terminal equipments,Peripherals,Host CPU,DTE,DCE,Modem,PCM,coder,PCM,decoder,DCE,Modem,DTE,ROP,Secondary CPU,Key elements of the fig.,1.Each device in the diagram,Analog,data,Keyboard/display,Fig.14-1:Simplified block diagram of a data communications link,Peripherals,Host CPU,DTE,DCE,Modem,PCM,coder,PCM,decoder,DCE,Modem,DTE,Keyboard/display,ROP,Parallel digital data,Serial digital data,Transmission media:Microwave,Twisted Pair or coaxial cable,Digital,T-carrier(cable),Secondary CPU,Terminal equipments,Key elements of the fig.,2.,arrows or lines,(Data flowing direction),Analog,data,Fig.14-1:Simplified block diagram of a data communications link,Peripherals,Host CPU,DTE,DCE,Modem,PCM,coder,PCM,decoder,DCE,Modem,DTE,Keyboard/display,ROP,Parallel digital data,Serial digital data,Transmission media:Microwave,Twisted Pair or coaxial cable,Digital,T-carrier(cable),Secondary CPU,Terminal equipments,Analog data,Key elements of the fig.,3.All the remark words beside the connection lines,Serial digital data,Peripherals,Host CPU,DTE,DCE,Modem,PCM,coder,PCM,decoder,DCE,Modem,DTE,Keyboard/display,ROP,Parallel digital data,Transmission media:Microwave,Twisted Pair or coaxial cable,Digital,T-carrier(cable),Secondary CPU,Terminal equipments,Simplified block diagram of a data communications link,Analog data,Serial digital data,Peripherals,Host CPU,DTE,DCE,Modem,PCM,coder,PCM,decoder,DCE,Modem,DTE,Keyboard/display,ROP,Parallel digital data,Transmission media:Microwave,Twisted Pair or coaxial cable,Digital,T-carrier(cable),Secondary CPU,Terminal equipments,Analog data,Source,Transmission media,Destination,Serial digital data,Peripherals,Host CPU,DTE,DCE,Modem,PCM,coder,PCM,decoder,DCE,Modem,DTE,Keyboard/display,ROP,Parallel digital data,Transmission media:Microwave,Twisted Pair or coaxial cable,Digital,T-carrier(cable),Secondary CPU,Terminal equipments,Simplified block diagram of a data communications link,Analog data,T,ranslation,In an,interruption,an asset of the system becomes lost or unavailable,or unusable.An example is malicious destruction of a hardware,device,erasure of a program or data file,or failure of an operating,system file manager so that it cannot find a particular disk file.,在,中断,情况下，系统资源开始丢失，不可用或不能用。例如，蓄意,破坏硬件设备，抹除程序或数据文件或造成操作系统的文件管理程,序故障，以致不能找到某一磁盘文件。,T,ranslation,An,interception,means that some unauthorized party has gained,access to an asset.The outside party can be a person,a program,or a,computing system.Examples of this type of failure are illicit copying,of program or data files,or wiretapping to obtain data in a network.,While a loss may be discovered fairly quickly,a silent interceptor may,leave no traces by which the interception can be readily detected.,截取,是指某一非特许用户掌握了访问资源的权利。外界用户可以是,一个人、一个程序或一个计算机系统。这种威胁的例子如程序或数,据文件的非法拷贝，或私自接线入网去获取数据。数据丢失可能会,很快被发现，但很可能截取者并不留下任何容易检测的痕迹,。,T,ranslation,If an unauthorized party not only accesses but tampers with an asset,the,failure becomes a,modification,.For example,someone might modify the,values in a database,alter a program so that it performs an additional,computation,or modify data being transmitted electronically.It is even,possible for hardware to be modified.Some cases of modification can be,detected with simple measures,while other more subtle changes may be,almost impossible to detect.,如果非授权用户不仅可以访问计算机资源，而且可以篡改资源，则威胁就,成为,修改,了。例如，某人可以修改数据库中的值，更换一个程序，以便完,成另外的计算，或修改正在传送的数据，甚至还可能修改硬件。某些情况,下可以用简单的测量手段检测出所做的修改，但某些微妙的修改是不可能,检测出来的。,,科技论文标题的写法,学术文章的标题主要有三种结构：,名词性词组,(,包括动名词,),，介词词组，名词词组,+,介词词组。,间或也用一个疑问句作标题,(,多用在人文社会科学领域,),，但一般不用陈述句或动词词组作标题。,一、名词性词组,名词性词组由名词及其修饰语构成。名词的修饰语可以是形容词、介词短语，有时也可以是另一个名词。名词修饰名词时，往往可以缩短标题的长度。以下各标题分别由两个名词词组构成。例如：,Latent demand and the browsing shopper(,名词词组,+,名词词组,),Cost and productivity(,名词,+,名词,),科技论文标题的写法,二、介词词组,介词词组由,介词十名词或名词词组,构成。如果整个标题就是一个介词词组的话，一般这个介词是,“,on,”,，意思是,“,对,的研究,”,。例如：,From Knowledge Engineering,to Knowledge Management(,介词词组,+,介词词组,),On the correlation between working memory capacity and performance on intelligence tests,科技论文标题的写法,三、名词,/,名词词组,+,介词词组,这是标题中用得最多的结构。例如：,Simulation of Controlled Financial Statements,(,名词,+,介词词组,),The impact of internal marketing activities on external marketing,outcomes(,名词,+,介词词组,+,介词词组,),Diversity in the Future Work Force(,名词,+,介词词组,),Models of Sustaining Human and Natural Development(,名词,+,介词词,组,),标题中的介词词组一般用来修饰名词或名词词组，从而限定某研究课题的,范围。这种结构与中文的,“,的,”,字结构相似，区别是中文标题中修饰语在,前，中心词在后。英文正好相反，名词在前，而作为修饰语的介词短语在,后。例如：,Progress on Fuel Cell and its Materials (,燃料电池及其材料进展,),科技论文标题的写法,四、其他形式,对于值得争议的问题，偶尔可用疑问句作为论文的标题，以点明整,个论文讨论的焦点。例如,：,Is B2B e-commerce ready for prime time?,Can ERP Meet Your,eBusiness,Needs?,科技论文标题的写法,有的标题由两部分组成，用冒号,(,：,),隔开。一般来说，冒号前面一部分是研,究的对象、内容或课题，比较笼统，冒号后面具体说明研究重点或研究方,法。这种结构可再分为三种模式。,模式,1,研究课题：具体内容。例如,：,Microelectronic Assembly and Packaging Technology,：,Barriers and Needs,The Computer Dictionary Project:an update,模式,2,研究课题：方法性质。例如,：,B2B E-Commerce:A Quick Introduction,The Use of Technology in Higher Education Programs:a National Survey,模式,3,研究课题：问题焦点。例如,：,Caring about connections:gender and computing,Thanks!,