| 摘要 |
A first apparatus includes a sending unit which attaches a sequence number which is numbered for each priority of QoS set in a first packet, the sequence number is numbered for each priority of QoS set in the first packet, and sends the first packet with the sequence number. A second apparatus includes a storage unit which stores, for each priority, a history of sequence numbers attached to packets received, a determining unit which receives the first packet from the first apparatus, identifies the sequence number of the first packet, and determines whether the first packet has been previously received by comparing the identified sequence number with the history of sequence numbers according to the priority of QoS set in the first packet stored in the storage unit, and a unit which discards, when the determining unit determines the first packet has been previously received, the first packet.
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