| 摘要 |
<p>Disclosed is a method and apparatus for detecting a fraudulent toll telephone call made by means of a device coupled to a telephone, which device can generate a single-frequency (SF) tone control signal and multi-frequency (MF) signals used in a toll telephone network. The method comprises the steps of: (a) identifying (11) an off-hook condition on a toll analogue SF trunk line by detecting loop current on the trunk, and (b) detecting (12) on the trunk an SF tone control signal indicating an on hook condition, followed (13) by a predetermined number of MF control signals. The fraudulent call can be cancelled by actuating (14)arelay having contacts in at least one control lead of the SF trunk.</p> |
