RACK_detect_reordering():
    For each Segment newly acknowledged, cumulatively or selectively,
    in ascending order of Segment.end_seq:
        If Segment.end_seq > RACK.fack:
            RACK.fack = Segment.end_seq
        Else if Segment.end_seq < RACK.fack AND
                Segment.retransmitted is FALSE:
            RACK.reordering_seen = TRUE