Patent 7525919 was granted and assigned to Nippon Telegraph and Telephone on April, 2009 by the United States Patent and Trademark Office.
When a lower layer address pair of a transferred lower layer frame is counted a predetermined number of times or more, a packet transfer apparatus (2) sends the lower layer address pair to a frame transfer apparatus (3). The frame transfer apparatus (3) counts the transfer frequency of the lower layer frame having the lower layer address pair.