Abstract: A method and apparatus of phase synchronizing a plurality of spatially distributed application modules having synchronizing clocks requiring synchronization, each application module being connected, at a predetermined site nearest the module, to an outgoing path and, at a corresponding site nearest the module, a return path of a pulse reference path, the method comprising the steps of injecting reference pulses at a predetermined frequency into an injection site of the reference path such that the pulses travel along the outgoing path to a remote site and return to the injection site along the return path; determining, for each application module, the time interval for each pulse to travel from the predetermined site to the corresponding site associated with the application module; monitoring, for each application module, the elapsed time interval for each pulse to travel between the predetermined and corresponding sites associated with the application module; producing, for each application module, a local p