| 摘要 |
PURPOSE:To obtain various information before response, by providing a control signal for a selection signal received/transmitted between a telephone set and an exchange at calling, and changing the sound volume or tone of the incoming telephone set. CONSTITUTION:Through the dial operation of a digital telephone set 1, a selection signal and a control signal representing name of a caller and emergency are transmitted to an exchange 4 at incoming side via an exchange 3 at calling side. The exchange 4 interpretes the received dial signal, selects the line of a telephone set 1' of incoming side, and transmits a call signal and the control signal via a multiplex separation circuit 2'. The telephone set 1' compares data set by a called party in advance with the transmitted control signal, the sound volume and tone are changed when they are coincident to go a sounder. Thus, the called party discriminates whether the call is an incoming call from a specific subscriber before response or not, and whether the call is the incoming call having high urgency. |
