Abstract: A network path test circuit for testing call connections established through the switch network of a telephone toll switching office. Common control equipment of the telephone toll switching office momentarily applies a tone signal to the transmit and receive paths of a call connection prior to outpulsing a called telephone station directory number. Detector apparatus measures the impedance reflected back over the call connection to determine the absence and existence of path transpositions in the call connection. The common control equipment is enabled to establish another call connection when the reflected impedance indicates path transpositions in the call connection.