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(From Wikipedia, the free Encyclopedia)
Note: A 440-Hz tone is applied to the line for 2 seconds, followed by a 0.5-second burst every 10 seconds, to alert both parties that the attendant is connected to the circuit.
Source: from Federal Standard 1037C
Source: the above text is adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Busy verification."
Copyright © Philip M. Parker, INSEAD. Terms of Use.