Far-end disconnect detector for telephony systems

A method for detecting a far-end disconnect signal in a telephone signal, which method comprises the steps of:

• determining a measure of the signal power of the telephone signal for predetermined frequency ranges and for predetermined time periods;
• at each predetermined time period, determining that the time period is characteristic of the far-end disconnect signal whenever the sum of the measures of the signal power for predetermined ones of the predetermined frequency ranges is (a) greater than the signal power for predetermined other ones of the predetermined frequency ranges and (b) greater than a predetermined measure and determining that the time period is non-characteristic otherwise;
• determining the number of consecutive time periods during which time periods are characteristic, determining the number of consecutive time periods during which the time periods are non-characteristic, and determining the number of consecutive cycles of such characteristic and non-characteristic consecutive time periods;
• and
• reporting that the far-end disconnect signal has been detected when a predetermined number of consecutive cycles has been counted, wherein the step of determining a measure of the signal power for predetermined frequency ranges and for predetermined time periods comprises the steps of:
• at each predetermined time period, applying the signal to a predetermined number of filters, said filters spanning the frequency range of typical human speech and far-end disconnect signals, with one or more filters covering the frequency range of far-end disconnect signals, and one or more filters covering the frequency range of typical human speech above and below the frequency range of far-end disconnect signals;
• and
• applying the output of each filter to a filter output power determination circuit to provide a measure of the signal power for each predetermined period of time.