一、通信网络的发展一百多年以前开始有了电话通信网,近30多年计算机的应用使数据通信网也有了快速的发展。随着科学、技术的进步及经济、文化的发展,发达国家电话业务容易迅速放大,非话业务,如传真、电报、电子邮件、数据通信视图文,可视电话、电视会议及高分辨率的静止和运动图象 First, the development of communications networks More than a hundred years ago began to have a telephone communications network, nearly 30 years of computer applications to the data communications network has also been rapid development. With the progress of science and technology and the economic and cultural development, the telephone service in developed countries can easily be amplified rapidly. Non-speech services such as fax, telegraph, e-mail, data communication view text, videophone, video conference and high resolution Still and moving images