个人收集整理资料， 仅供交流学习， 勿作商业用途
附录4：英文资料及中文翻译
1.英文资料
Communicating with Datal
Data signals are transmitted over various types of telephone circuits.They travel on wire from telephone pole to telephone pole,through underground cables,from mountain top to mountain top over microwave facilities, on the ocean floor in submarine cables, and via communications satellites from continent to continent. Some type of data conversion equipment is required to change the digital machine signals to a form suitable for transmission over these facilities.b5E2RGbCAP The data machine which provides an input to the transmit section of the conversion equipment, or modulator ,can be a keyboard , printer, card reader, paper tape terminal computer or magnetic tape terminal. The output from the receive section of the converter, or demodulator, can be applied to a tape punch, printer, card punch, magnetic tape unit, computer, or visual display terminal. Typically, both the modulator and demodulator sections of the converter are combined into a two-way data transmitter-receiver, commonly called a data modem or data set.p1EanqFDPw The typical full-duplex data transmission system including the originating data processing equipment and the interface assembly which consists of buffer and control units. The interface assembly at the transmitter accepts data at the rate determined by the operating speed of the data processor. stores the data temporarily, and regenerates it at a rate compatible with that of the data modem. At the receiving terminal the interface assembly accepts the received data, stores it, then feeds it to the data processor at the appropriate rate.DXDiTa9E3d Timing signals from the interface assembly at the transmitter are applied to the data modem to synchronize the
1 / 12
个人收集整理资料， 仅供交流学习， 勿作商业用途
computer and the data set .At the receiver, synchronization pulses are derived from the data stream to synchronize the computer.RTCrpUDGiT When more than one data set feeds into a computer, the capacity of the interface equipment is of major concern since it must determine the time slot allocation for each line. Various types of interface assemblies are employed, such as magnetic core memories, shift registers, and delay lines. Not all data communications terminals employ an interface between the data processor and the data modem. Without an interface, the input, data transmission, and output functions proceed simultaneously and at the same rate of speed. 5PCzVD7HxA Since data signals are rarely in suitable form for transmission over the various types of transmission facilities, a signal coding process is normally performed. Ideally, the transmission medium should have linear attenuation and delay characteristics, but this is never so in practice, and transmission impairments are always present to disturb the data signals. As a comparison, in voice communications a high degree of transmission irregularities can be tolerated. If a voice circuit has a heavy loss or is noisy, the speakers compensate automatically by increasing the intensity of their voices. If words are missed because of transmission difficulties, they are often understood anyway because of the redundant nature of speech. In contrast, there is no inherent redundancy in data signals unless purposely inserted and, therefore, transmission variations car only be compensatedfor over a very small range. In addition, data signals are sensitive to other transmission impairments which have little effect on speech.jLBHrnAILg Coding is undertaken to alleviate transmission irregularities, to increase the information capacity of the system, to enable error detection, and to provide message security. The coding process in the data transmitter simply
2 / 12
个人收集整理资料， 仅供交流学习， 勿作商业用途
rearranges the applied data machine signals into some other format. At the receiving end the reverse processing is performed to recover the original machine signals.xHAQX74J0X The diagrams show the two types of information signals that are applied in digital form to a data modem. Shown in A is a binary non-return to zero signal. In B the same signal is shown in the return to zero format. The difference between A and B is that in A successive marks or spaces follow one another, whereas in B there must be a return to the space level between successive marks. The voltage values of marks and spaces are arbitrary and may be positive, negative, or both.LDAYtRyKfE Of primary concern when considering the transmission of data from one deviceto another is wiring. And of primary concern when considering the wiring is the data stream. Do we send one bit at a time, or do we group bits into larger groups and. if so, how? The transmission of binary data across a link can be accomplished either in parallel mode or serial mode. In parallel mode, multiple bits are sent with each clock pulse. In serial mode, one bit is sent with each clock pulse. While there is only one -way to send parallel data, there are two subclasses of serial transmission: synchronous and asynchronous.Zzz6ZB2Ltk Asynchronous transmission is so named because the timing of a signal is unimportant. Instead, information is received and translated by agreed-upon patterns. As long as those patterns are followed, the receiving device can retrieve the information without regard to the rhythm in which it is sent. Patterns are based on grouping the bit stream into bytes. Each group, usually eight bits, is sent along the link as a unit. The sending system handles each group independently, relaying it to the link whenever ready, without regard to a timer.dvzfvkwMI1 3 / 12
新型消防车研究中英文翻译
