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D70-type automatic switching system (1983)

The structure of this model integrated the functions of a local switch (LS), toll switch (TS), and local tandem switch (MS), with a processing capacity of 4,800 erlangs. It was a switching system intended for stations operated by NTT and covered nearly all of the stations in Japan.
It was introduced in 1983, and was used in high volume until the replacement of all NTT switching systems to digital types in 1997. During the period until this replacement, plans were made to reduce its size and cost, and to strengthen its processing capacity so it could respond to the shift of subscribers to optical services as well as the increase in traffic, and a revised D70-type automatic switching system was introduced in 1993.