| 摘要 |
A system and a method for screening dial tones that are transmitted by a customer's touch-tone communication device (CCD) to a destination's communication device (DCD). The system comprises a screening device (DCD). The system comprises a screening device that enables receiving and transmission of dial tones, detecting the pitch and the frequencies of each received genuine dial tone, generating of random dial tones and intersecting the random dial tones and intersecting the random dial tones through the sequence of the genuine dialed tones that are transmitted by the customer through the telephone line.
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