An exemplary method and apparatus are provided for transmitting an asynchronous transport signal over an optical fiber section of an Optical Transport Network. Higher order Optical Data Units of an asynchronous transport signal to be transmitted may be encapsulated into outer transport frames that offer a payload rate higher than a nominal bit rate of the asynchronous transport signal. An output optical signal, which contains the outer transport frames with the encapsulated asynchronous transport signal, is generated at a locally generated clock rate and transmitted over an optical fiber section. To encapsulate the asynchronous transport signal, its bit rate is adapted to the payload rate of the outer transport frames, which is derived from the locally generated clock through a justification and stuffing process. The rate adapted transport signal is then synchronously mapped into the outer transport frames at the rate of the locally generated clock.