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对于远离电话局的地区,架设电话难于做到经济及技术上都十分合理,为此,有必要研究出一种新的通信方式。 富士通在日本电信电话公社的指导下,对人口过疏地区用的数字用户线系统进行了研究。1975年已投入使用的SM—D1方式,就是综合了增量调制、数字多路复用等传输技术和
For areas far from the telephone office, it is difficult to make telephone calls economically and technically very reasonable. Therefore, it is necessary to study a new communication method. Under the guidance of Nippon Telegraph and Telephone Corporation, Fujitsu has conducted research on the digital subscriber line system for overpopulated areas. The SM-D1 method, which was put into use in 1975, is a combination of transmission techniques such as delta modulation and digital multiplexing