a call classifier for recognizing cadenced signals is based on data tables whose contents define the cadences of the signals that need to be recognized . consequently , the call classifier may be adapted for recognizing the cadenced signals of various signaling schemes that are used in various countries or telecommunication systems , simply by reprogramming the data contents of the data tables . each cadenced signal comprises a different pattern of interleaved signal - on intervals and signal - off intervals . a separate cadence timing table - pair corresponds to each sequential s / p interval - pair . each table - pair includes a p table and an s table each having a plurality of entries each corresponding to a different duration of the corresponding p interval and s interval , respectively , and identifying those signals which have the corresponding p interval and s interval duration , respectively , as candidates for a received signal . the durations of sequential ones of the p and s intervals of the cadence pattern of the received signal are measured and applied as pointers to sequential ones of the cadence timing table - pairs to select the corresponding table entries . the selected table entries are anded with each other until only one candidate remains in the result . the one candidate identifies the received signal . because reception of a signal can begin anywhere within the signal &# 39 ; s cadence pattern , the table - pairs are initially used to identify when the end of one and the beginning of another instance of the cadence pattern has been received .