Abstract: When a failure detection server calculates a measurement average value at every predetermined time with respect to measured values collected in the past, and collects measured values from cable modems, the server sets a failure determination threshold value by adding or subtracting a predetermined difference threshold value to or from the measurement average value so as to determine the presence of failure. A failure analysis server performs a screening process of inputting determined failure information and eliminating logically conflicting failure information, obtains a differential of the screened failure information between this time and previous time so as to extract changed failure information and newly generated failure information, and then, repeats state determination at an upstream connection point, starting from a cable modem having failure information, so as to estimate the failure generated location.

Abstract: Gate switches can switch an amount of attenuation, and are set in a distributed manner on distribution lines and a trunk on subscribers' house side in a CATV transmission path having a tree structure with an optical node that follows a headend being taken as a starting point. An upstream-transmission-quality monitoring unit monitors an S/N ratio of an upstream signal obtained from an upstream port having the headend connected thereto to detect a decrease in upstream transmission quality based on a degree of decrease and a continuation state of an S/N ratio. When the upstream-transmission-quality monitoring unit detects a decrease in upstream transmission quality, a noise-generation-source searching unit performs a sequential switching control over the amount of attenuation at the gate switches provided on the CATV transmission path from upstream to downstream to search for a source of generation of upstream ingress noise.

Abstract: When a failure detection server calculates a measurement average value at every predetermined time with respect to measured values collected in the past, and collects measured values from cable modems, the server sets a failure determination threshold value by adding or subtracting a predetermined difference threshold value to or from the measurement average value so as to determine the presence of failure. A failure analysis server performs a screening process of inputting determined failure information and eliminating logically conflicting failure information, obtains a differential of the screened failure information between this time and previous time so as to extract changed failure information and newly generated failure information, and then, repeats state determination at an upstream connection point, starting from a cable modem having failure information, so as to estimate the failure generated location.