| 摘要 |
<p>PURPOSE:To attain effectively the privacy call of a party line telephone set using a digital line by providing a ciphering and a deciphering section to a telephone set and a subscriber circuit, and decoding information based on an ID (calling telephone set identification number) transmitted from an opposite party. CONSTITUTION:The party line telephone system is constituted by connecting plural digital telephone sets 1, 2 and a switch network 5 by a digital subscriber circuit 4 and a digital line 3. Further, an individual ID signal transmitting means and a ciphering/deciphering means are provided in the telephone sets 1, 2, and the ciphering/deciphering means is provided also in the subscriber circuit. Thus, when a call is made from a telephone set and the ID signal is transmitted to the subscriber circuit 4, the circuit 4 performs ciphering by using the ID signal. In this case, other telephone sets can not make a call. At the incoming call to the telephone set, only the telephone set coincident with the incoming IC signal transmitted from the subscriber circuit is decoded. In case of common mutual talking, a common ciphering pattern to both the telephone sets is indicated from the subscriber circuit 4.</p> |
