In a passive optical tree-and-branch network, which utilizes the Asynchronous Transfer Mode (ATM) transmission format, a superimposed low-level, single frequency, ranging signal is used to determine the distance between an Optical Line Termination (OLT) node and any Optical Network Termination Node (ONT) of the network. In one embodiment of the invention, this ranging frequency is a low frequency signal that is superimposed on top of the transmitted data signal from the OLT. This ranging signal is returned to the OLT from a particular ONT upon the issuance of a ranging command from the OLT. The phase difference between the transmitted ranging signal and the received ranging signal is proportional to the distance between the OLT and that particular ONT. In a second embodiment of the invention, the ranging signal is a high frequency signal that is superimposed on top of the transmitted data signal from the OLT. This ranging signal is returned to the OLT from a particular ONT upon the issuance of a ranging command from the OLT. The time between issuance of the ranging command and reception from that particular ONT of the ranging signal is proportional to the distance between the OLT and the ONT.