外文翻译--数据通讯.doc

英文资料： 1、Data Communications The 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 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 computers 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 important 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. Basically, 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 communications 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 subscriber’s equipment. Several different types of computer peripherals may appear 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 term