Data transmission method and unit

摘要

An in-house paging system includes a call controller connected to an in-house switching unit for providing an interfacing process in response to a call request from an extension terminal. A plurality of transmitting units are connected to the call controller through a signal line and a power source line. A pager terminal is provided for notifying a maintenance staff of a call signal from a transmitting unit on receipt of the signal. The transmitting unit comprises a detecting unit for detecting whether or not an abnormal condition arises in a signal line or a power source line to a call controller and a signal/power-source line abnormal signal transmitting unit for transmitting abnormal condition information to the pager terminal when the detecting unit detects an abnormal condition in the signal line or the power source line. A battery as a backup power supply unit is used in case of power disconnection.