Patent ID: 7616721

Claim:
A network synchronization clock checking apparatus of a communication system, comprising: a clock generator for generating a reference clock signal having a predetermined frequency; a network synchronization clock unit for counting a number of reference clock signals generated for a time corresponding to a predetermined period of an externally input network synchronization clock signal so as to calculate a value of the predetermined period of the externally input network synchronization clock signal; a divided clock unit for generating a divided clock signal having a same frequency as the externally input network synchronization clock signal based on the reference clock signal, and for counting a number of reference clock signals generated for a time corresponding to a predetermined period of the divided clock signal so as to calculate a value of the predetermined period of the divided clock signal; and a comparator for comparing the value of the predetermined period of the externally input network synchronization clock signal to the value of the predetermined period of the divided clock signal so as to output an indication of whether the externally input network synchronization clock signal is normal.