| 摘要 |
PURPOSE:To send call signals to a terminating subscriber by audible sound signals from a calling telephone set by any times even when the terminating subscriber on-hooks after off-hooking by connecting an audible sound signal detecting circuit to the subscriber's circuit of a terminating subscriber's telephone set. CONSTITUTION:In accordance with the calling from the originating subscriber's telephone set TELB to a terminating subscriber's telephone set TELA, a relay A is actuated by a signal from a central processor CC in the subscriber's circuit and a calling signal is sent to the TELA. When the TELA is off-hooked, a calling signal stop detecting circuit RD is actuated and the CC restores a relay B by said actuation. The relay B is actuated by the DC ring formed by the TELA and the communication line between the TELA and TELB is completely connected. When the TELA is on-hooked under said state, the relay B is restored, the audible sound signal detecting circuit TD is ready to receive, so that an audible sound signal from the TELB is detected, the relay A is actuated and the calling signal is sent to the TELA. |
