Abstract: A bi-directional data transmission system that facilitates communications between a central unit and a plurality of remote units using a frame based discrete multi-tone (DMT) transmission scheme is disclosed. The discrete multi-tone data transmission system has a multiplicity of discrete subchannels including an overhead bus. In a method aspect of the invention, frames transmitted from the plurality of remote units are synchronized at the central unit. When a selected remote desires to initiate communications, it loop times it own clock to the clock of the central unit and transmits a remote initiated synchronization signal to the central unit over a dedicated overhead subchannel in the overhead bus. The central unit responds with a centrally initiated synchronization signal that contains information indicative of a frame boundary phase shift required to synchronize the selected first remote unit with other remote units that are currently communicating with the central unit.