与必须表达在用户驻地和本地开关之间的ISDN服务，发信号继续称D渠道的一条分开的数字通道。
With ISDN service, signaling that must be conveyed between the user station and the local switch is carried on a separate digital channel called the D channel.
该产生器由输入整形、分频器、数字开关移相器、延迟秒形成、本地秒形成等电路组成。
The generator is composed of input shaping circuit, frequency divider circuit, numeric switch phrase shifter circuit, delay second formation circuit, local second formation circuit and so on.
当开关被用作互相联络的装置时，本地网络的地理范围，理论上来说，是没有限制的。
When switches are used as interconnection devices, there is no theoretical limit to the geographical reach of a LAN.
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