Rapid expansion in the use of private automatic branch exchanges. Development of remote alarm equipment for unattended exchanges.
用户自动交换机迅速普及。开发无人交换机远端报警设备。
Rapid expansion in the use of private automatic branch exchanges. Development of remote alarm equipment for unattended exchanges.
用户自动交换机迅速普及。开发无人交换机远端报警设备。
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