| 摘要 |
PURPOSE:To decrease the number of transmission lines provided to each trunk by providing a simple control part and a switch, and using one transmission line efficiently by plural switchboards. CONSTITUTION:To one transmission line 200, exchanges 10, 20, 30, and 40 are connected through branch devices 210 and 220. To each exchange, an automatic switchboard 6 and a control circuit 5 are connected through trunks. A dial signal after channel selection, sent from the dial trunk of the automatic switchboard of one station is sent to a transmission line 200 together with an added station number through the operation of a switch when the dial signal of another station does not arrive, and when the dial signal arrives, a different switch operates to send a busy tone to a sound output terminal. At an opposite station, when a received dial signal arrives, a control circuit 5 discriminates whether it corresponds to the station number of the station and when so, a switch constitutes a calling circuit while a dial signal removed from the station number is outputted to a signal output terminal. |
