第15章电子信息类专业英语(第二版)课本李白萍.ppt

Unit Three Data Communications Unit Three Data Communications Passage A Data Communications Passage B Characteristics of Communication Channels Passage C Communication Equipment and Software Passage A 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.[1] 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. 　　Initially, both the airline and banking operations can be established on a private basis, which would minimize the need for switching operations. But in both cases, the need to expand beyond private operations soon arises. In the case of the airlines, the need arises to access the facilities of other airlines; and in t