Comments by "kd1s" (@kd1s) on "Phone Buttons - Numberphile" video.

  1. The period of the mid 50's through the 1960's were an interesting period in telephonic development. Bell had been using push buttons for operator consoles prior. But the other biggie from the mid 50's on was the DDD network. Used 4A Crossbar initially, then later 4E completely digital switch.
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