随着微机的普及,各种微机网络的应用,例如国内外的各种BBS站,尤其是用户最多、资源量惊人的国际最大微机网络——INTERNET,使网络热达到了高潮,微机的通信也成了微机的重要功能之一。目前,多数普通电脑用户都是通过MODEM加电话线采用拨号方式来进行网络访问或进行远程点对点通信的,当然,电信部门也提供一些其他的专用数据接口,但不适用于普通个人用户。我们通常使用的电话,其线路上传输的信号是模拟的,在程控电话交换机中被称为模拟用户线路,它的使用特性我们已经比较了解;在程控数字交换机 With the popularization of microcomputer, the application of various computer networks, such as various BBS stations at home and abroad, especially the international largest computer network with the largest number of users and the huge amount of resources - INTERNET, has brought the network fever to climax. The communication of microcomputer Has become one of the important functions of the microcomputer. At present, most ordinary computer users use dial-up mode to access the network or perform remote peer-to-peer communication through MODEM and telephone lines. Certainly, the telecommunications department also provides some other special data interfaces, but it is not suitable for ordinary individual users. We usually use the phone, the signal transmitted on the line is analog, in the program-controlled telephone switch is called analog subscriber line, its use of the characteristics we have more understanding; in the program-controlled digital switch