Patent ID: 7805119

Claim:
A method for detecting a T1-N0 signal at a multiline communication node, the multi-line communication node comprising two or more communication lines, the method comprising: (a) subjecting a single frequency input signal in the communication line to a complex filter substantially passing all of the frequencies in the predetermined set of frequencies, to produce a complex filtered signal (b) for each of one or more pairs of members of the complex filtered signal (a+bj) and (c+dj) (i) determining a complex number Y d having a phase indicative of a phase difference between the two members of the pair; (ii) determining the frequency of the input signal based upon the one or more complex numbers determined in step (b)(i); (c) for each of the one or more predetermined frequencies (i) outputting a Dbit value associated with the predetermined frequency if the current frequency of the filtered signal is equal to the predetermined frequency; (ii) outputting a Dbit value of n if the current frequency of the filtered signal is not equal to any one of the predetermined frequencies, to generate a sequence of Dbits; (d) analyzing the sequence of Dbits to detect the T1-N0 sequence; and (e) connecting the communication line to the modem when the T1-N0 sequence is detected in the communication line.