| 摘要 |
PURPOSE:To attain channel test by utilizing a call tone to test the channel thereby eliminating the need for the provision of a channel test tone transmission circuit. CONSTITUTION:A call tone transmission circuit 12, a call tone detecting circuit 13, and a terminal interface 18 are connected via a channel of a telephone exchange 11. The terminal interface is provided with channels 15, 16, a reflecting talking switch circuit and a terminal interface terminal 17. A call tone is transmitted from the call tone transmission circuit 12 to the terminal interface 18 via the telephone exchange 11, the terminal interface reflects the call tone at the switch circuit 14 and returns it to the telephone exchange 11. The returned call tone is detected by the call tone detecting circuit 13 and used for the discrimination of the propriety of the channel. |
