专业英语datacom教案.ppt

The software controls the flow of this data. The necessary hardware consist of a modem and telephone lines. 软件控制这些数据的流动,硬件中调制解调器和电话线是必须的. The modem modulates the computer output to an acceptable signal for transmission and then demodulates the signal back for computer input. 调制解调器调制计算机的输出信号成为适合传输的形式,然后将返回计算机的信号解调出来. The modem on the transmitting computer converts the digital signals to modulated analog signal tones and transmits them over the telephone lines. 发送端计算机的调制解调器把数字信号调制为模拟信号,并通过电话线发送出去. The receiving computer’s modem transforms the incoming analog signals back to their digital equivalents in order to understand them. 为了便于理解,接收端计算机的调制解调器变化输入模拟信号回到同等的数字形式. Transmission rate The transmission rate of a communications channel is determined by its bandwidth and its speed. 信道的传输速率是由信道的带宽和信息传输速率决定的. The bandwidth is the range of frequencies that a channel can carry. 带宽是信道能运载信息的的频率范围. 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. 由于传输的数据被分配到不同的频率进行传输,因此,这将有更宽的带宽,或者更多的传输频率,也将有更多的数据被同时传输. The speed at which data is transmitted is usually expressed as bits per second or as a baud rate. 数据传输的速率通常表示为比特率或者波特率. Bits per second (bps) is the number of bits that can be transmitted in one second. Bps 一秒传输的二进制码元个数. Use a 10-bit byte to represent a character (7 data bits, 1 start, 1 stop, and 1 parity bit), a 2400 bps transmission would transmit 240 characters per second. 用一个10位二进制字节去代表一个字符(7个数据位,1个开始位,1个结束位,1个奇偶效验位), 2400bps的传输速率就意味着每秒传输240个字符. At this rate, a 20, single-spaced report would be transmitted in approximately five minutes. 以这样的速率传输一个单栏20页的报告将大概需要5分钟. The baud rate is the number of times per second that signal being transmitted changes. 波特率是每秒被传输信号的变化次数. 《通信与信息工程专业英语教程》 * The type of data communication facility used is a function of the nature of the application, the number of computers involved, and their physical interface. * 1.Physical - C