数据通讯DataCommunications中英文对照

1、英文资料：1、data communicationsthe rapid growth of data communications has been influenced primarily by the increasing need to move information to and from computers. modern time-shared computers can communicate with many data stations simultaneously. other forms of data transmission which the telephone

2、and telegraph lines are called upon to handle are batch data transmission, real-time transmission (as in the case of airline reservation systems), banking and credit data, man-computer conversation with the aid of graphics, data collection systems and automatic meter reading the combination of compu

3、ters and data communication places such new requirements on the systems, which must handle them, that one can refer to them better as teleprocessing rather than telecommunications. teleprocessing started with the airline reservation systems, where the distribution of computer data is not as importan

4、t as the maintenance of an inventory of seats for the whole system and the ability to access such an inventory rapidly at a number of distant points. another example is that of the banks, who desired to centralize their accounting and provide access to a central file for all their branches. basicall

5、y, there are three reasons for the development of teleprocessing systems: the requirement for centralized files, the need to distribute computer services and the advantage gained by having flexibility in location of the operating staff which utilizes the system.the most applicable model for data com

6、munications requirements is the central computer conversing with many simple terminals simultaneously. differing from telephone communications, a data communications network must be able to interconnect a wide variety of subscribers equipment. several different types of computer peripherals may appe

7、ar as network terminals, and so also can computers functioning in several different ways. terminal speeds ranging from 100 bits per sec to 10,000 bits per sec are likely to be important. many terminals in current use are constrained by the available communications services, but many of the have vari

8、able speeds. one approach to this situation is to provide a buffer store at the terminal, but this approach is expensive. at present, multi-access computers usually handle terminals of only one speed or with a small number of fixed speeds. it has been proposed that feedback from the output device be

9、 used to permit one simple output program to drive terminals with different characteristics. of course, such feedback signals would have to be handled by the communications network.at data technology develops, each multi-access computer is connected to an increasing number of terminals, making it ex

10、pensive and difficult to provide separate lines from the computer to the network for each of the terminals. thus, a need for multiplexed connections between the computer and the terminals arises. but this need cannot necessarily be met in a straightforward manner. one characteristic of a data commun

11、ications network differing from conventional telephone networks is that the two ends of the communication link are very different. one end is a computer capable of flexible behavior, and the other end is a relatively slow terminal with no intelligence. since the two ends are so different, it would a

12、ppear that the network would communicate differently with them. the flow of information in a data communication system is intermittent just as it is in the case of telephone conversations however, instead of minutes of conversation, only a few seconds will elapse for the information flow in one dire

13、ction, followed by a pause and some flow of information in the opposite direction, the access times for typical computers in use at this time are about 100 ms , but this will become faster as better memories are utilized . the time scale for the interchange of data messages needs to be of this order

14、. 2、characteristics of communication channelsdata communications is the electronic transmission of information including data ,television pictures, sound and facsimiles. it usually involves s computer, a modem , software, and a printer. with this equipment, you can communicate with a friend in st. l

15、ouis, missouri, or paris, france, sending and receiving anything from a manuscript to a simple message over the telephone lines. using the same method, a home-bound child can interact with a teacher in the classroom, an office worker can work at home, and a doctor can access a remote computer for re

16、search data. the reasons for using communications system are convincing. it is expedient and efficient, lessens job stress, decreases car pollution, saves time and money, allows the home to serve as an office, promotes distant learning in which students can share information and computer research fi

17、ndings.when you connect one computer to another, you use hardware and software. in the majority of cases, the hardware consists of equipment that sends the data over some type of communications line, such as a telephone line. the software controls the flow of this data. the necessary hardware consis

18、t of a modem and telephone lines. the modem modulates the computer output to an acceptable signal for transmission and then demodulates the signal back for computer input. the modem on the transmitting computer converts the digital signals to modulated analog signal tones and transmits them over the

19、 telephone lines. the receiving computers modem transforms the incoming analog signals back to their digital equivalents in order to understand them.transmission ratethe transmission rate of a communications channel is determined by its bandwidth and its speed. the bandwidth is the range of frequenc

20、ies that a channel can carry. since transmitted data can be assigned to different frequencies, the wider the bandwidth, the more frequencies, and the more data can be transmitted at the same time.the speed at which data is transmitted is usually expressed as bits per second or as a baud rate. bits p

21、er second is the number of bits that can be transmitted in one second. using a 10-bit byte to represent a character, a 2,400bps transmission would transmit 240 characters per second. at this rate, a 20-page, single-spaced report would be transmitted in approximately five minutes. the baud rate is th

22、e number of times per second that signal being transmitted changes. wing each change, one or more bits can be transmitted. at speed up to 2,400 bps, usually only one bit is transmitted per signal change and, thus, the bits per second and the baud rate are the same. to achieve speeds in excess of 2,4

23、00 bps, more than one bit is transmitted with each signal change and, the bps will exceed the baud rate.direction of transmission the direction of data transmission is classified as either simplex, half-duplex, or full-duplex. in simplex transmission, data flows in one direction only. simplex is use

24、d only when the sending device, such as a temperature sensor, never requires a response from the computer. for example, if a computer is used to control the temperature of a building, numerous sensors are placed throughout it. each sensor is connected to the computer with a simplex transmission line

25、 because the computer only needs to receive data from the temperature sensors and does not need to send data back to the sensors. in half-duplex transmission, data can flow in both directions but in only one direction at s time. an example is a citizens band radio. the user can talk or listen but no

26、t do both at the same time. half-duplex is often used between terminals and a central computer. in full-duplex transmission, data can be sent in both directions at the same time. a normal telephone line is an example of full-duplex transmission. both parties can talk at the same time. full-duplex tr

27、ansmission is used for most interactive computer applications and for computer-to-computer data transmission.1、数据通讯数据通讯迅速增长主要被增长的需要影响了移动信息计算机。现代分时操作的计算机可能同时联络许多数据站。电话和通信机线被要求处理是批数据传输, 实时传输的其它数据传输的形式(在飞机订票系统情况下), 在图表的帮助下，与智能计算机交谈完成开户和信用卡业务, 在这种计算机中安置这样新方式的数据收集系统、自动计算机和数据通讯的组合系统, 必须处理他们的数据, 一个可能提到他们更好

28、作为远程处理数据而不是电信。远程处理开始以飞机订票系统, 计算机数据发行像电子存货维护不是一样重要使整体系统和能力迅速地访问这样存货在一定数量遥远的地方。其它例子如银行, 对于一个中央文件集中他们的会计和为所有他们的分支提供存取。基本上, 有远程处理的系统的发展的三个原因: 集中文件的处理要求, 需要计算机维护系统和由地方人员灵活操作的计算机系统。最可适用的模型为数据通讯要求是中央计算机同时交换以许多简单地方的数据终端信息。与电话通信不同, 数据通讯网络必须能够互联各种各样的用户的终端设备。几不同的类型计算机外围有不同网络终端, 也和计算机的作用及功能上用几个不同的方式。终端速度范围应在从10

29、0 位每秒到10,000 位每秒是相对比较重要。当前使用的许多数据在终端具有各种可利用的通讯服务, 但它们有各种不同的速度差。对这个情况有一种方法是终端提供缓冲单元, 但这种方法是昂贵的。当前, 多通道计算机通常处理仅仅一种速度终端或以很小数量固定范围内的速度。就出现通过反馈输出设备的可应用简单输出程序来驱动不同特征的终端设备。当然, 这样反馈信号会必须通过通讯网络处理。随着数据通讯技术的发展，每个多通道计算机被连接到终端设备数目在不断的增长数字, 使它造价昂贵和难提供把计算机和网络中每个终端分开所许的电线。因而, 出现在计算机和终端之间更加复杂的连接方式。但这并不需要采用适应的直接方式。数据

30、通讯网络的一个特征是不同与常规电话网, 这两种通信线路的两个目是非常不同的。一个末端是具有灵活方式的计算机处理能力,而另一末端是一个相对地缓慢没有智力的终端。因为两个目的是很不同的,就会出现在网络数据通信中的不同连接方式。在电话谈话情况下信息流程在数据通讯系统是断断续续的。然而, 在信息的交谈中，在几秒中信息只有在一个方向上流动, 被暂停的信息和一些跟随的信息在相反的方向上流动, 目前所用的典型计算机存取时间大约为100毫秒，但采用较好的存储器时存取时间将会缩短。时间表对于数据信息交换作为一种命令方式使用。2、通信频道的特征数据通信是电子信息传输包括数据、视频图像、声音和传真. 它通常是一些电脑、调制解调器、软件和打印机. 拥有这些设备,你还可以与在圣路易斯密苏里、或法国的巴黎、英国，通过电话线路收发任何一个简单的信息. 用同样的方法,一家孩子可以与老师在课堂上上课, 上