| 摘要 |
PURPOSE:To introduce the same communication service as the service being used to an extensible subscriber line switchboard of an incoming trunk class without altering the switchboard by performing incoming operation differently according to whether a terminating terminal call signal is present or not. CONSTITUTION:When an incoming signal from a host station arrives at a circuit correspondence device 4 and an incoming detecting circuit 40 is actuated, the incoming is transmitted to a control circuit 46. When the circuit 40 discriminate a 16Hz ringing signal from the host station, a ringing detecting circuit 41 detects and sends it to the circuit 46, which trips the circuit 40 to stop the 16Hz ringing. When the circuit 40 receives and discriminates a 1,300Hz call signal after the tripping, an audible ringing tone detecting circuit 42 detects and sends it to the circuit 46, which confirms at specific timing that the call signal continues for a specific time. An indication is sent to a current supply circuit 43 after the confirmation to place the channel of a subscriber line 5 in a through state, and the call signal is received by a terminal device 6 with an automatic receiving function. When the terminating operation of the device 4 is completed, namely, if the 1,300Hz call signal is not received after the tripping of the circuit 40, an incoming connection with a TEL7 is made. |
