A method for operating a media-access control unit in communications network includes placing the unit in a scan mode where the cyclic-prefix length and frame length of frames of data transmitted by a base station are ascertained and one or more parameters relating to the signal quality of the base station are collected. Data is not exchanged with a higher protocol-layer unit during this scan mode. The method also includes the unit remaining in the scan mode until at least a point in time when the unit is receiving frame control headers at an interval equal to the ascertained frame length. The unit is thereafter placed in a run mode in which the unit processes at least one flow of data to the higher protocol-layer unit once the cyclic-prefix length and the frame length are ascertained.