Bell Telephone Laboratories

Lucian Philip Fabiano, Jr

John Francis O'Neill

Theras Gordon Lewis

James Owen Dimmick

An electronic key telephone system is disclosed in which connections among the station sets and telephone lines are made in a central time division switching network remote from the station sets. Each station set and line is equipped with a port circuit having an individual shift register for defining the time slot interval during which a connection may take place. To assign a time slot to a port circuit, the main controller interrogates the network to find an idle time slot and then furnishes that time slot number to the network controller. In order to save central memory and to increase system reliability, the main activity memory which stores an indication of which ports are or should be interconnected in the network need not contain any reference to the time slot number assigned for the particular connection. In order periodically to verify that actual network connections reflect the state of the activity memory, two types of audits are performed. A fast audit accesses the activity memory to find an active port and then accesses the network to find the time slot assigned the port. If no time slot or more than one time slot are assigned, an error indication results. A slow audit is performed which steps through all idle port circuits and which clears network connections for ports whose activity memory indicates an idle state but for which a network time slot is found.

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Madrid, Spain

Lucian Philip Fabiano, Jr