HARDWARE OF D-20 ELECTRONIC SWITCHING SYSTEM.

The D-20 electronic switching system, developed for application to small and medium size telephone offices, is a switching system based on stored program control with a maximum capacity for 16,000 subscriber lines (800 erlangs) and 19,000 busy hour calls. Technical advances have been actively introduced by adopting the overlay technique for call processing programs, and using IC memories. As a result, it has been possible to realize economically a stored program control system which provides versatile telephone services and abundant maintenance functions, as well as to achieve a high availability and small floor space requirements.