Telephone Call Progress Detection Method
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2005-Feb-19
This invention relates to a method for detecting any one signal condition in a set of signal conditions representing the progress of a call in a telephone system. The set of signal conditions consists of dial, busy, ringback, data set, and voice signals. The method steps include (a) sampling and noise thresholding the zero axis crossings of the signal condition of any telephone call in progress, and (b) comparing the thresholded signals with reference values and providing indication upon a match. The method relies upon the observation that different signal conditions have different "zero axis crossing signatures". The telephone system signal input to the invention is taken from an FCC-approved Direct Access Arrangement (DAA) or equivalent, as shown in Fig. 1.