Abstract: A method for marshalling an additional outstation (3) of a time division multiple access (TDMA) telecommunications system including a basestation (4) and a plurality of outstations (1, 2), such as a passive optical network (PON). A sequence is transmitted from the additional outstation (3) to the basestation (4) at a level below the noise sensitivity of a receiver (49) of the basestation (4), detected at the basestation and its phase discrimated. From the discriminated phase the loop delay to the additional outstation is determined and the outstation instructed to realign its transmission accordingly. The sequence and its phases are detected by a correlation process. (FIG. 1).