Call progress signal monitor and method for telephone systems

A call progress signal monitor for distinguishing call progress tones in a PCM bit stream, comprising:

• means being responsive to PCM bytes for providing code values in a range being defined by predetermined limits of maximum and minimum values corresponding to negative and positive sign PCM bytes of maximum value;
• means being responsive to a series of the code values for generating a series of trend codes, at least one of the trend codes being unique to indicate an occurrence of an increasing trend in the code values changing to a decreasing trend in the code values;
• and
• detection means being responsive to the code values and the trend codes for detecting progress tones in accordance with predetermined characteristics in a series of code value occurrences in combination with a series of trend code occurrences.

In a call progress signal monitor, a method for generating data signals being indicative of predetermined characteristics in a bit stream of plural bit encoded positive and negative signal samples, comprising the steps of:

• translating each instant occurring sample into an instant data word having a code value with reference to a predetermined reference value corresponding to at least a maximum possible value of the samples;
• comparing the code value of each instant data word with the code value of an immediately previously occurring data word, and generating a comparison value signal in response to each of the comparisons;
• encoding a combination of each instant comparison value signal and a plurality of its consecutive predecessors to generate trend codes;
• each of the data signals being comprised of the code value of said instant data word and a corresponding instant trend code.

A method for machine distinguishing a call progress signal as typically is used in a telephone system, comprising the steps of:

• translating signal samples from a communication path in the telephone system into corresponding data words each having a code value in a range being defined by predetermined limits of maximum and minimum values, wherein maximum amplitude positive and negative sign signal samples each correspond to a respective one of said limits, and
• deriving a first frequency component in a series of the signal samples as a reciprocal of an average period of time between ones of the signal samples occurring with extreme code values in a direction toward one of said limits, whereby the highest frequency component in a call progress signal is defined;
• in response to the extreme code values being dissimilar, deriving an envelope frequency component as a reciprocal of a period of time between the extreme code values occurring with a greatest value difference, and
• deriving a second frequency component as a difference of the envelope frequency being subtracted from the first frequency whereby a frequency component being lower than the highest frequency component is defined in the call progress signal.