At+t Corp.

At&t Bell Laboratories

Jerome J Zelenski

Douglas A Spencer

Ronald K Witmore

David M Kissel

Michel L Hearn

Michael J English

Jeffrey A Williams

A port system interfaces digital PBX's to any transmission facility having DSX-1 communications ports via a microprocessor controlled PBX port board connected between PBX switch fabric and a first DSX-1 communications port. A channel service unit (CSU) module coupled directly to the port board for communications with DS1 transmission lines defines a second DSX-1 communications port which is coupled to the first DSX-1 communications port. The CSU module also includes a T1 transceiver and line interface circuitry for coupling the CSU module to a DS1 transmission line. The combination of the port board and CSU module provide full functionality of conventional CSU's while the port board alone permits direct coupling of transmission facilities utilizing a DSX-1 communications port. For remote maintenance, a microprocessor of the port board is coupled to a control processor of a PBX for control of the port board microprocessor via the PBX control processor. Wiring test circuitry is provided in the CSU module to detect faults in the wiring between a CSU module and a DS1 transmission line. The CSU module includes a transmitter transformer having a center-tapped secondary winding and a receiver transformer having a center-tapped primary winding. A current limited current source is selectively connected between the center taps of the transmitter and receiver transformers such that, when connected, one or more transformers in a CSU/DS1 interface circuit which is faulty will saturate leading to failure of transmission tests and hence proper detection of the fault.

Port system for interfacing digital PBX to digital transmission facility

A time division, digital switching system capable of performing on-line testing of the actual communications paths that are switched is disclosed. When an idle network time slot is found, a test vector register places a stimulus in the idle time slot and the stimulus is directed to the address of an idle port. A loop-around path which includes a signature analysis chip (SAC) device is activated to divert a portion of the stimulus toward the SAC device. The response of the SAC device is gated to a maintenance circuit which reads the generated signature. Advantageously, the stimulus is selected to generate minimum noise at the addressed port so that if the user at the idle port picks up the telephone during the time slot used for testing, no loud noise will be heard.

Maintenance of stored program controlled switching systems

Growing community of inventors

Broomfield, CO, United States of America

Jerome J Zelenski