Abstract: A communication switching system of PABX uses a number of time division multiplexed send and receive highway pairs each servicing a plurality of peripheral devices or ports providing two-way communication with the outside world by means of associated telephones, trunk line interfaces, or similar apparatus. All highway pairs are multiplexed in accordance with the same time division format and the maximum number of two-way peripheral devices serviced by each highway pair is dependent on the number of time slots of the format assigned for audio communication. Each peripheral device transmits on a given audio time slot of its send highway. Switching to establish communication paths between peripheral devices is achieved in part by receiving means in each peripheral device responsive to command signals transmitted on command time slots on the associated receive highway instructing each peripheral device on which audio time slots of its receive highway to receive.

Abstract: A processor controlled communication switching system or PABX uses time division multiplexing with pulse width modulation of audio signals. Switching to establish communication paths between peripheral devices serviced by the system is distributed among the peripheral devices and controlled by command signals issued to the peripheral devices by a processor implemented common control. All peripheral devices transmit to the common control on a communication send line and receive signals from the common control on a communication receive line. The particular illustrated system services up to fifty two-way peripheral device ports and is inherently nonblocking.

Abstract: A private automatic branch exchange (PABX) telephone system includes a number of stations connected to a transmission cable by appliques. By digital messages sent over a communication line in the cable, in signalling and supervision time slots, the appliques communicate with one another to make and break talking path connections between stations, which talking path connections utilize other time slots of the communication line, and to perform other signalling and supervision functions. A system clock broadcasts timing signals to the appliques over a timing line in the cable, separate from the communication line, to synchronize the operation of the appliques and to define the time slots into which the usage of the communication line is broken. The system clock also maintains traffic on the communication line by detecting the end of each signalling and supervision message and by initiating a new message upon the detection of such end of message.