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接触过局域网络(LAN)的人,大多认为安装、使用LAN十分方便.特别是Novell的NetWare,基本上只要求用户熟悉DOS,而加上对网络命令稍许了解,使用网络完成日常工作便没有什么问题.但是LAN最大的不足在于连接的距离太近,然而实际应用中,连接距离往往超过这一要求.这就要求有经济、实用的方法实用远程连接.另外,国内证券业的发展,特别是股票市场的建立,对如何远距离传送信息提出了新的要求.因为象股票这一类信息,不但要求快速,而且要求准确.这就要求在通信速度和可靠性方面都上一个档次.不论是远程LAN互联也好,还是远程通信也好,人们首先想到的自然是利用现存的电话网络.不过因为电话网络是为传送模拟的话音信号而设计的,计算机所处理的信号(0,1组合)是数字信号,所以就要引入一种设备来完成数字信号在模拟线路上的传送.这种设备便是本书讨论的调制解调器(Modem).
Most people who have been exposed to a local area network (LAN) think it is very easy to install and use a LAN, especially Novell’s NetWare basically only requires users to be familiar with DOS, but with a little knowledge of network commands and nothing to do with daily work using the Internet However, the biggest disadvantage of LAN is that the connection distance is too close, but in practical applications, the connection distance often exceeds this requirement, which requires economical and practical method for practical remote connection.In addition, the development of the domestic securities industry, especially The establishment of the stock market has put forward new requirements on how to transmit information over a long distance, because information like stocks requires not only fast but also accurate requirements, which requires a higher level of communication speed and reliability. Remote LAN interconnection is good, or long-distance communication Ye Hao, people first think of the nature is to use the existing telephone network.But because the telephone network is designed to transmit analog voice signals, the computer signals (0,1 combination) Is a digital signal, so it is necessary to introduce a device to complete the digital signal transmission in the analog line. This device is the modulation of the book discussion Demodulator (Modem).