created by multiplying two sinusoids. When analyzed in the frequency domain, a modulated tone looks like three tones. Figure A-4 shows the frequency spectrum for a modulated tone. The tone whose frequency is the average of the other tones is the carrier. The other two tones can be referred to as side lobes. For amplitude modulated tones, frequencyl and bandwidth1 specify the low sidelobe and its tolerance, while frequency2 and bandwidth2 specify the high sidelobe and its tolerance. INSERT GRAPH Figure A-4: Frequency Domain Representation of Tone Parameters for an Amplitude Modulated Tone As with dual tones, not all modulated tones will be detected by UTD. Modulated tones shall be detected if the difference between the carrier frequency and the sidelobes is between 10 Hz and 230 Hz. A.5.3.l.4 Precedence By assigning a detection precedence to the classification process, tone frequency ranges can overlap. When a tone's parameters fall into a range shared by two or more signals, the signal is classified as the one with the highest precedence. Software License D2 Technologies, Inc. and Maintenance Agreement August 4, 1997 CONFIDENTIAL 32 ------------------------------------------- Precedence Call Progress Signal ------------------------------------------- 1 Modem 2 FAX CNG 3 Audible Ringback 4 Busy 5 Reorder or Congestion 6 Number Unobtainable 7 SIT 8 Dial Tone 9 Unknown Tone ------------------------------------------- Table A-6: Tone Detection Precedence Table A-6 shows the precedence of typical tones that the UTD module detects. Modem signals have the highest precedence, and Unknown tones have the lowest. Therefore, the frequency range of unknown tones can safely overlap the other tone ranges without causing tones to be misclassified. If the range for Unknown tones is allowed to be the maximum range allowed by the detector, any detected tone that is unclassified would be designated as Unknown. A.5.3.1.5 North American Call Progress Signal Detection Functional