| CPC H04L 63/1416 (2013.01) [H04L 63/1483 (2013.01); H04L 67/12 (2013.01)] | 7 Claims |
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1. A signal detection apparatus comprising:
a signal detection unit which detects signals expected to be input to a communication network in a predetermined cycle; and
a determination unit which determines whether detection timing of a second signal detected by the signal detection unit after a first signal which is set as a reference signal for determining an illegal signal is in a predetermined range within which reference timing that is timing after an integer multiple of the cycle from detection timing of the first signal falls among the signals detected by the signal detection unit, and whether a shift between the detection timing of the second signal and the reference timing is a first threshold or less, wherein
the determination unit
sets the second signal as the reference signal when the shift between the detection timing of the second signal and the reference timing is the first threshold or less,
sets the first signal as the reference signal without setting the second signal as the reference signal when the shift between the detection timing of the second signal and the reference timing exceeds the first threshold,
determines that the detection timing of the second signal is in the predetermined range within which the reference timing falls when the shift between the detection timing of the second signal and the reference timing is a second threshold or less, wherein the first threshold is less than the second threshold,
determines that the second signal is a normal signal when the detection timing of the second signal is in the predetermined range, and
determines that the second signal is not a normal signal when the detection timing of the second signal is not in the predetermined range, and determines whether the second signal is an illegal signal based on information included in the second signal or/and another signal input to the communication network.
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