PURPOSE: To facilitate processing without any need for a special scanning device to inform a switchboard body of trip detection, by effectively utilizing a DC loop monitoring function provided to a subscriber circuit.
CONSTITUTION: According to the indication from a central controller CC, a howler control circuit CTL controls a howler signal source HW-OSC2 and a howler trip monitoring circuit HWTR2, and also controls a loop signal sending circuit LOP which sends out a loop signal to a switchboard side. The switchboard side, when detecting the off-hook of a handset, operates switches SW1 and SW2 to send a howler signal to the subscriber. At this time, a DC loop signal is sent from the sending circuit LOP to a subscriber circuit LC2 and when the on- hook of the subscriber is detected by a howler trip monitoring circuit HW-TR2, a DC loop-break signal is sent out of the LOP to the subscriber circuit LC2 and the switchboard body is informed of that.
YASOJIMA NOBUYUKI
KOGA TOKUJI
HOSOKAWA MINEO
