Abstract: A method of lowering the power absorbed by an interface circuit, in the "power-down" state thereof, as incorporated to a telephone exchange and connected to a telephone subscriber line, being of a type which comprises a monitoring circuit portion connected between the line and the exchange. The method involves the steps of,detecting the polarization level of a conductor in the line,comparing that level with a reference value by means of a comparator having an input connected to the line and an output connected to the input of the monitoring circuit portion,switching the interface circuit to a standby state on a higher level than the reference value being sensed,once again detecting the polarization level of the line, this time through the interface circuit, andactivating the telephone exchange when, on completion of the second detection step, the polarization level stays above the reference value.

Abstract: A method of attenuating the echo signal in so-called telephone fork converting circuits, adapted for telephone conferences with a plurality of participants, consists of switching and arranging sequentially on a serial line messages from each participant as coded in the PCM code, by means of a digital switching array, and of performing a sign reversal on the PCM codings of a number of messages equal to the approximation to the nearest number below the number of participants in the conference divided by two.

Abstract: A method of lowering the power absorbed by an interface circuit, in the "power-down" state thereof, as incorporated to a telephone exchange and connected to a telephone subscriber line, being of a type which comprises a monitoring circuit portion connected between the line and the exchange. The method involves the steps of,detecting the polarization level of a conductor in the line,comparing that level with a reference value by means of a comparator having an input connected to the line and an output connected to the input of the monitoring circuit portion,switching the interface circuit to a standby state on a higher level than the reference value being sensed,once again detecting the polarization level of the line, this time through the interface circuit, andactivating the telephone exchange when, on completion of the second detection step, the polarization level stays above the reference value.