An embodiment of a method for processing data units is provided that includes receiving a plurality of data units, of a data stream, having respective sequence numbers and, employing a reordering window, determining whether a newly received data unit of the data stream is a new data unit or a repeated data unit at the receiver and defining a first and a second range of sequence numbers relative to the sequence number of a previously received data unit. A newly received data unit is determined to be either a new or a repeated data unit based on whether the sequence number of the newly received data unit falls within the first or second range, and processed at the receiver based on this determination. A handover condition is detected, and in response thereto the first and second ranges of the reordering window are adjusted for use during the handover condition.