We are aiming at introducing a solution to a consensus problem, which models the a-synchronous part of a clock synchronization problem. The solution is based on the diffusion of a request from the peripheral units to the privileged units that respond with the value of a reference clock that is diffused in the opposite direction. The diffusion is controlled by a hierarchical arrangement of the units, which operate following a 3-state self-stabilizing algorithm. The overall behavior is modeled as a series of waves that propagate in the system, and that are periodically triggered by peripheral units. The appendix contains the exhaustive proof of the formal claims contained in the paper.