Multiparty line adapter with privacy feature controlled by reversal of line polarity at a central power source

In a shared subscriber line arrangement, a multiparty line adaptor circuit interposed between a subscriber subset and a central or local telephone exchange for enabling a plurality of subscribers to share a telephone subscriber line such that privacy is maintained at all call stages between the subscribers sharing the line, said circuit comprising:

• line interface means coupled to the subscriber tip and ring lines for providing a transmission path from the shared subscriber line selectively either directly to the subscriber subset or to a circuit path through said multiparty line adaptor circuit;
• signalling receiver means coupled to said line interface means for receiving subscriber identity signals from said subscriber line and for generating a digital logic code indicative of receipt of a particular identity signal, said code being coupled to a control means for interpretation by said control means;
• signal transmitter means coupled to said signalling receiver means responsive to the interpretation of said code by said control means for generating and transmitting a unique identity signal indicative of the identity of a subscriber;
• and
• control means for decoding said logic signal from said signalling receiver to generate a plurality of commands for selective enabling and disabling of said multiparty line adaptor circuit such that only calling and called parties have access to said subscriber line while a call is in progress.

In a telephone communication system wherein a plurality of multiparty lines each having a plurality of individual subscribers sharing each subscriber line communicate with a central exchange through a multiparty line adaptor circuit, a method of implementing a reverting call comprising the steps of:

• STEP 1--detection at the central office of a calling subscriber going off-hook.
• STEP 2--performing a battery voltage reversal at the central office which disconnects all subscribers from the line and enables all multiparty line adaptor circuits;
• STEP 3--transmitting an interrogation signal from the central office to enable signal transmitters of all multiparty line adaptor circuits;
• STEP 4--transmission from the calling subscriber's multiparty line adaptor circuits of an identification signal to the central office for enabling transmission from the calling subscriber to the central office;
• STEP 5--returning to normal the battery polarity at the central office to connect the calling subscriber to the subscriber line while maintaining all other subscribers in a disconnected condition from the subscriber line such that the calling subscriber can dial a called subscriber. The calling subscriber dials a called subscriber;
• STEP 6--the central office recognizes the called subscriber to be on the calling subscriber line;
• STEP 7--performance of a battery polarity reversal at the central office;
• STEP 8--transmission of a dual tone multifrequency identification signal from the central office to the called subscriber, to establish a communication path between the central office and the called subscriber.