Programmable port sense and control signal preprocessor for a central office switching system

A community office switching system includes a three-level hierarchy of distributed processors operating in parallel with one another to control the operation of a central office matrix switch network interconnecting 1,920 ports. At the highest level, a stored-program call control processor controls call progression, establishing paths through the matrix switch network. At the second level, a series of special-purpose, stored-program, port control processors each service 960 ports, sensing and transmitting supervisory signals and communicating the occurrence of significant port events to the call control processor. Each port event control processor dedicates approximately 32 microseconds out of every 32 milliseconds to each of the 960 ports in time-multiplexed fashion, and hence no port can ever be locked out at the port-control-processor level. One from a series of stored programs is executed to service each port precisely one every 32 milliseconds. At the lowest level, a digital filtering processor, associated with each port control processor, samples some signals from each port once every millisecond, filters the sampled signals to give one filtered sample every four milliseconds, and stores the filtered samples for presentation to the associated port control processor once every 32 milliseconds.