| 摘要 |
PURPOSE:To realize a privacy call between remote subscribers and at the same time to ensure a free switching between a normal call and a privacy call, by deciding the intervention of a privacy telephone device with a switching signal. CONSTITUTION:The digital privacy telephone devices 6 and 6' are connected to each other with 4 wires for a call between remote subscribers, i.e., telephones 1-1 and 1-2. An exchange 5' detects a call between remote subscribers with a dial number and transmits a switching signal to a switching signal detection/ switch driving circuit 9 of devices 6 and 6' to change switches S21 and S22 to the sides of dotted lines. Through this switching, the privacy signal scrambled by a privacy device 11' is descrambled to be converted into a digital signal. This digital signal is turned into an analog signal through an MODEM13 and sent to the privacy device of the remote side to be supplied to carrier end offices 4-2 and 4-4 by scrambling. In such a way, the deterioration can be prevented for the sound quality of the privacy call between telephones 1-1 and 1-2. At the same time, free switching is ensured between a normal call and a privacy call. |
