It is a set of equipment enabling two or more persons or groups in different places to hold real-time conferences by means of mutual transmission of sounds, videos and documents through a transmission line and multimedia devices. It is a typical image communication system. At its transmitting end, image and sound signals are converted into digital signals; at its receiving end, the digital signals are converted into visual and auditory information again. Compared with an audio conferences system, it has massive information, a strong visual impression, etc. It enables conference participants to hear sounds, see each other and discuss about problems and study drawings and other physical objects together, creating almost the same effect as real conferences.