SETT OCH ANORDNING VID AUTOMATISKA HUSTELEFONCENTRALER

摘要

1531671 Automatic exchange systems SODECO-SAIA AG 19 Jan 1977 [26 Jan 1976] 02140/77 Heading H4K The use of telephone extensions of a PABX is detected by periodically feeding tone pulses into active exchange lines and detecting those tones at the extension lines. As shown line current in an exchange line 4 of a PABX7 is detected at 2. Immediately thereafter and after each exchange metering pulse as detected at 1, a monitoring unit 5 repeatedly transmits a train of tone pulses via a coupling unit 4 to the line. A filter 18 prevents the tones reaching the exchange. The trains are verified in a detector 14 individual to the extension line involved. The detector transmits the line identity to monitoring unit 5 where it is printed or logged for billing.