Prevention of broadband cable service theft

Abstract

Detecting tampering of an incoming cable to which a network interface unit (NIU) is connected by testing for the reflected signal that is present when the signal being transmitted to the head end is not connected to a properly terminated coaxial cable. In particular, by comparing the phase of the transmitted signal from the NIU with that of the reflected signal, a distinction can be made between a signal that travels many feet before being reflected back and a signal that reflects back right or near the connector of the NIU. Only the latter is used as a stimulus to indicate tampering since the first is likely caused by cable personnel disconnecting the cable further into the network. The key difference between the two types of reflected signals is the time delay of the reflect signal with respect to the transmitted signal from the NIU. The method can be used to detect a bridge tap, because the tap causes the characteristic impedance of the cable to decrease causing an infeed mismatch and subsequent reflected energy. When tampering or a bridge condition is detected, the NIU disrupts service by disabling the video signal to the residence, disable Internet access, and disable telephony service with the exception of 911 calls and calls to the service provider. To restore service, the cable service provider intervenes and sends a specific data sequence to the NIU in order to restore service. The cable service provider then can investigate and determine the reason for the disruption.