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ISDN是综合业务数字网,俗称“一线通”。DDN是利用数字信道传输数据信号的数据传输网。帧中继是从X.25分组通信技术演变而来的。HDSL是利用现有电话网中使用的普通铜线实现高速率、全双工数字信号传输的技术。
ISDN is an integrated business digital network, commonly known as “one-pass.” DDN is the use of digital channels to transmit data signals data transmission network. Frame Relay evolved from X.25 packet communication technology. HDSL is the use of ordinary copper wire in the existing telephone network to achieve high-speed, full-duplex digital signal transmission technology.