| 摘要 |
The invention relates to a circuit arragement to prevent unauthorised operations, especially the unauthorised dialling of other subscribers, on a wired telephone system with leads using modular units. It is the purpose of the invention to provide a circuit arrangement which prevents unauthorised persons from tapping into the line between the exchange and the phone terminal, which is user-friendly, economical and independent of the operating system and can be both easily fitted to existing telephone systems and integrated into new ones. The circuit arrangement of the invention forms a control system of modular units A and B, in which unit A is fitted on the main distribution frame with the subscriber connection unit in the exchange and unit B is fitted between the TAE socket and the telephone so that only when the phone terminal is in authorised use are both modular units and an exchange of knowledge between them involved in the line loop existing between the phone terminal and the exchange during the conversation. |
