二十一世纪,各方面对信息的依赖越来越大,人类正进入信息时代。随着经济的迅猛发展,通信的信息量巨增。数字数据网这一具有高速、快捷、高质量的综合传输业务的电信网络产生了,它具有:接入灵活;传输速率高,网络时延小;全透明传输等优点。在话音、图形、图像和视频等多媒体通信中得到广泛应用。在许多邮电通信工程中,为满足传输图像、话音、数据等业务需要,DDN作为主要通信方式。 In the 21st century, all parties are increasingly relying on information and mankind is entering the information age. With the rapid economic development, the amount of information in communication has increased dramatically. Digital data network with high-speed, fast, high-quality integrated transmission of telecommunications network has emerged, it has: access to flexible; high transmission rate, small network delay; full transparency and so on. It is widely used in multimedia communication such as voice, graphics, image and video. In many post and telecommunications projects, DDN serves as the primary communication method to meet the business needs of transmitting images, voice and data.