A method for detecting the use of public address systems in private automatic domestic telephone central and circuit arrangement for carrying out the method

摘要

A circuit arrangement for detecting the use of telephone extensions in an automatic private branch exchange 9 with a plurality of internal lines 5 to 8, wherein an identifying signal is fed into the subscriber line 13 and, after passing the exchange 9, is derived from one of the internal lines 5 to 8, to indicate for storage and analysis the extension which set up or took over the telephone connection with an outside subscriber. The arrangement also includes a safeguard means 15 for detecting and displaying the occurrence of faults on any of the internal lines 5 to 8. IMAGE