Public telephone clip-on fraud prevention system

Abstract

To prevent so-called 'clip-on' fraud from occurring at a public telephone station, such as a coin operated public telephone, a unique signature identifier is transmitted at the telephone following the transmission of the dialed number. If remote equipment determines that the expected identifier is not correct, or it fails to receive the signature, then the remote equipment terminates the call. Once the call is completed, then the public telephone is expected to periodically transmits a second identifier. The completed call may also be terminated if the remote equipment does not receive the expected second identifier at an expected rate or if a received second identifier is not correct.