Abstract: An apparatus and method are provided for a data communications device, such as a modem (100,101), software modem, or facsimile machine, to detect and discriminate various amplitude modulated signals, such as an ANS signal of the ITU V.25 protocol and an ANSam signal of the ITU V.8 protocol. The apparatus and method embodiments first determine the presence of a first frequency component in a received signal, such as the 2100 Hz component of ANS and ANSam signals (205). The received signal is then demodulated (215) and low pass filtered (220), followed by removing any resulting direct current component (225) to form an inclusive signal. A second frequency component, such as the frequency of the 15 Hz amplitude modulating component of an ANSam signal, is removed from the inclusive signal (235), and its resulting magnitude is determined, as a filtered signal magnitude (240). The filtered signal magnitude is subtracted from the magnitude of the inclusive signal (230) to form a discrimination value (245).

Abstract: Apparatus for detecting single and/or multiple cadenced tone progress status of a telephone call in any one of a plurality of telephone networks is disclosed. A set of parameters for each of a multiplicity of predetermined single and/or cadenced tones in which some call progress status having multiple different sets of parameters for the same call progress status are stored in memory. Parameters of the cadence (s) of a valid tone present on the telephone line are measured and compared with the multiplicity of sets of parameters stored in the memory to establish the presence of the call progress status represented by the corresponding cadenced valid tone. For tones having multiple cadences, the measured parameters of each cadence is compared with a corresponding set of cadence parameters of the memory to establish the presence of the call progress status represented by the multiple cadenced tone.