Communications: Electronic telephone switching in Japan: For Nippon Telegraph and Telephone, D-10 and D-20 are ¿household¿ words, as is ¿ESS¿ in the U.S.
M. Shiromizu · IEEE Spectrum · 1976
Since 1964, NTT's (Nippon Telegraph and Telephone) Electrical Communication Laboratory has worked on the development of electronic switching systems with four manufacturing companies. The consortium has produced the D-10 system for large offices, the D-20 system for small and medium offices, and the D-10-R1 remote control system for extensions in existing offices.