Fundamentals of stored program control of telephone switching systems

The Bell System has initiated the commercial installation of stored program controlled telephone switching systems. The main purpose for introducing stored program control is to provide flexible systems where additions and changes can be introduced primarily through program modification rather than through changes in hardware. This brief tutorial paper discusses the general organization of these new systems. The basic elements touched upon include control, storage, scanning, signaling, switching, and some associated real-time problems. A description of a simple call is given in order to show how the basic elements of the system fit together. The paper concludes with a brief discussion of redundancy and other techniques used to meet telephone system reliability and maintenance requirements.