Dr. Hiroshi Inose's pioneering contributions to digital switching systems and his outstanding leadership in informatics

The idea of time slot interchange (TSI), the fundamental concept of implementing time switches in digital switching systems, was first conceived by Dr. Hiroshi Inose, then at the University of Tokyo, Japan, in 1957 while he was a visiting consultant at Bell Telephone Laboratories. The TSI collects each subscriber's pulse code modulation (PCM)-coded voice information to be stored into a small time interval (time slot), and then aligns multiple time slots on a common transmission bus to constitute a repetitive frame. The TSI enables any time slot to be interchanged with another time slot within a frame once the time slots in the frame are buffered in memories. Thus, TSI gives the time switch functionality equivalent to N-input by N-output space switch functionality. He built a prototype digital time-division multiplexing (TDM) electronic switching system called CAMPUS, which is based on the TSI principle, using a magnetostrictive delay line as a memory device. TSI received little attention until the end of the 1960s because memory devices were very costly. However, with the rapid advancement of semiconductor technologies in the 1970s, the TSI scheme became more widespread. TSI was first commercially deployed in 1976 as the time switch of AT&T's no. 4 ESS, the world's first stored-program control time-division switching system. Since then, TSI has been used in almost all digital central office switching systems and digital private branch exchanges (PBXs). Dr. Inose's contributions were not limited to research on such things as switching systems, PCM integrated communications, computer communications, and road traffic control systems; he was also actively involved in a number of Japanese governmental and international activities in the area of communications and information processing technologies. His final work was the establishment of the National Institute of Informatics (NII) in 2000, Japan's sole comprehensive academic institute in the field of informatics that seeks to advance integrated research and development activities in information-related fields.