Universal line concentrator

Claim 1

A TELEPHONE LINE CONCENTRATING SYSTEM COMPRISING A PLURALITY OF PAIRS OF FIELD AND CENTRAL OFFICE UNITS, EACH OF SAID FIELD UNITS BEING CONNECTED TO A PLURALITY OF SUBSCRIBER LINES, AND EACH OF SAID CENTRAL OFFICE UNITS BEING CONNECTED TO A PLURALITY OF RESPECTIVE LINE CIRCUITS; A RESPECTIVE PLURALITY OF VOICE COMMUNICATION TRUNKS EXTENDED BETWEEN EACH PAIR OF SAID FIELD AND CENTRAL OFFICE UNITS; RESPECTIVE CONTROL CONDUCTORS EXTENDED BETWEEN EACH PAIR OF SAID FIELD AND CENTRAL OFFICE UNITS; AND COMMON CONTROL MEANS CONNECTED TO EACH OF SAID CENTRAL OFFICE UNITS, AND COMMON CONTROL MEANS INCLUDING (1) MEANS FOR SCANNING ALL OF SAID LINE CIRCUITS FOR SERVICE REQUESTS, MEANS FOR TRANSMITTING SIGNALS OVER SAID CONTROL CONDUCTORS TO SAID FIELD UNITS TO CONTROL THE SCANNING OF ALL OF SAID SUBSCRIBER LINES FOR SERVICE REQUESTS, MEANS FOR CONNECTING SAID LINE CIRCUITS TO SAID TRUNKS RESPONSIVE TO SERVICE REQUEST AND FOR TRANSMITTING SWITCHING INFORMATION OVER SAID CONTROL CONDUCTORS TO CAUSE SAID FIELD UNITS TO CONNECT SAID SUBSCRIBER LINES TO SAID TRUNKS; (2) MEANS FOR SCANNING SAID TRUNKS TO DETERMINE RELEASE REQUESTS OF SAID TRUNKS, MEANS FOR DISESTABLISHING THE CONNECTIONS BETWEEN THE LINE CIRCUITS CONNECTED TO SAID TRUNKS RESPONSIVE TO SAID TRUNK ELEASE REQUESTS, AND FOR TRANSMITTING SWITCHING INFORMATION OVER SAID CONTROL CONDUCTORS TO CAUSE SAID FIELD UNITS TO DISESTABLISH THE CONNECTIONS BETWEEN THE RESPECTIVE SUBSCRIBER LINES AND SAID TRUNKS; AND (3) MEANS FOR DETECTING THE INTERCONNECTION OF ANY TWO TRUNKS IN THE SAME PLURALITY THROUGH TWO CONNECTED LINE CIRCUITS IN THE SAME PLURALITY, MEANS FOR