Electronic time-division-multiplexed pabx telephone system

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. The system clock also may repetitively broadcast some signalling and supervision messages of its own over the communication line. Except for these functions performed by the system clock, the system operates substantially entirely through the appliques and no common or central control equipment is required. Any number of appliques may be incorporated into the system, up to its maximum capacity, by merely connecting the appliques to the transmission cable, with each applique being connectable to the cable at any desired point therealong and being capable of being moved from one point to another to change the physical location of stations without interferring with the operation of the system.