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Chulak William: Remote testing system for communication circuits. Northern Electric Company, July 4, 1972: US3674947 (6 worldwide citation)

A connection to a test trunk circuit and associated test circuit at an outlying central office is dialed from a test center, eliciting a short reply tone pulse as a signal to restore local circuits manually from the dialing to the testing connection. This last operation causes the local circuits to ...


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