Abstract: This invention pertains to a method and arrangements that provide automatic detection of sequences of signals which previously required listening by operators in telephone systems to identify them. In a telephone system, certain information is transmitted using preselected signal sequences of tone bursts and silent intervals. These signal sequences are subjected to interference by speech and noise occurring in the telephone system. An arrangement is disclosed which reliably recognizes and identifies these signal sequences notwithstanding the apparent modification thereof due to the interference. In the process of recognizing these signal sequences, a three-stage recognition test is utilized to classify the durations of tone bursts and silent intervals in the signal sequences that occur. The validity of the signal sequence is checked by detecting inconsistent durations within the sequences. This feature is also utilized to indicate faulty apparatus used to generate these signal sequences.

Abstract: This invention pertains to systems servicing coin operated telephones and, more specifically, to apparatus in such systems for preventing called party fraud in simulating coin deposit signals. During intermediate coin deposit periods, the network connection between the calling and called stations is split into calling and called portions and then these portions are extended and reconnected. A filter is inserted in the extended called station portion to attenuate fraudulent coin deposit signals originating from the called station. A coin tone detector connected to the extended calling station portion is still actuated by valid coin deposit signals from the calling station, but does not detect the attenuated fraudulent signals.