SCHALTUNGSANORDNUNG ZUR UEBERWACHUNG EINER FERNSPRECHANSCHLUSSLEITUNG

摘要

A circuit for monitoring a telephone line in which a first wire (Ia) and a second wire (Ib) are connected to a telephone set (FE) which includes a control unit (SE) and a hookswitch (GU). A line-monitoring unit (LU) is connected between the first wire (Ia) and the second wire (Ib) ahead of the hookswitch (GU) and is coupled via a status line (ZL) (busy/idle) to the control unit (SE). The control unit (SE) is connected to an additional contact (S) of the hookswitch (GU) to simulate an off-hook condition of the telephone set (FE) for interference purposes upon receipt of a status message (busy) which does not agree with any of the conditions of the telephone set known to the control unit (SE) (improper parallel seizure). This arrangement interferes with unauthorised calls and is suitable for coin box telephones. <IMAGE>