Bell Telephone Laboratories

Theras Gordon Lewis

Donald Gifford Hill

Patrick A Vachon

John Francis O'Neill

James Owen Dimmick

Lucian Philip Fabiano, Jr

A network control circuit which allows time division switching systems of different sizes to operate with the same port circuit is disclosed. The time division switching systems utilize a port circuit with a ring counter which controls connection of the circuit to a system bus for establishing telecommunications paths. Each port circuit is provided with a ring counter which has one stage per time slot for the largest size switching system. A network control circuit generates commands which control circuitry associated with the ring counter to write bits into stages of the ring counter causing connection during appropriate time slots. When the port circuit is used with the largest sized switching system, one bit is written into the counter causing one connection per system cycle. In order to use the port circuit with switching systems that have fewer time slots, the network control generates commands to write two or more bits into the ring counter causing the ring counter to appear as if it had fewer stages.

Network control circuit for a time division switching system

A time division switching system is disclosed having a plurality of telephone line circuits and common control circuits for switching calls over a time division communication bus. Ringing loop current detectors are shared by groups of the line circuits for detecting call answer signals during active ringing on a call and for controlling the line circuits to interrupt, or trip, the ringing upon a called party answer. Each group of the line circuits is permanently connected to a ringing current supply via an individual one of the loop current detectors. Each line circuit includes ringing control circuitry operated and released by the common control circuits for connecting ringing current to a called line during an active ringing interval and for disconnecting it during a silent interval of the ringing cycle. The circuitry is responsive to a detection of a called station answer signal by the shared loop current detector for immediately tripping ringing. Apparatus is also provided in the circuitry for sensing answer signals during the silent intervals and for generating switchhook status signals during both the silent and active ringing intervals.

Ringing control circuitry with shared ringing loop current detector

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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Boulder, CO, United States of America

Theras Gordon Lewis