TRUNK CIRCUIT

PURPOSE:To urge the on-hook of a calling subscriber and to shorten the ineffective holding time of a talking by increasing the level of the transmission ringing tone to the calling subscriber as the unanswered time as a called subscriber increases. CONSTITUTION:When a calling subscriber 1 is connected to a trunk circuit, a connection detecting circuit 2 detects the connection of the trunk circuit and starts a counter 10 with a set signal S. At the same time, a switching circuit 3 is actuated to lead the circuit 2 into a ringing tone detecting circuit 9. The ringing tone of a fixed level given from a ringing tone generating circuit 7 is sent to the subscriber 1 via a ringing tone amplifier 12, the circuit 9, the circuit 3 and the circuit 2. The circuit 9 applies an input signal I to the counter 10 after detecting a ringing tone. The counter 10 counts the intermitting times of the signal I and supplies the count value to a decoder 11. The decoder 11 supplies an amplification degree control signal to the amplifier 12 in response to the count value.