| 摘要 |
A system and a method for screening dial tones that are transmitted by a customer's touch-tone communication device (CCD) [10] to a destination's communication device (DCD) [20]. The system comprises a screening device [100] that enables receiving and transmission of dial tones, detecting the pitch and the frequencies of each received genuine dial tone, generating a random dial tones and intersecting the random dial tones through the sequence of the genuine dialed tones that are transmitted by the customer { 10] through the telephone line. |
