PACKET TRANSFER METHOD, PACKET TRANSFER DEVICE, AND PACKET TRANSFER SYSTEM

An edge router measures a traffic volume inputted into a network, and the measurement result is notified to a network management server. If the network management server judges that the notified traffic volume is "smaller" than a capacity of a second core router, it will direct a first core router to shift to a power saving mode. The first core router notifies the edge router of the shift to the power saving mode, and the edge router updates a routing table so that the packet to the first core router may be bypassed to the second core router. The first core router shifts to the power saving mode that does not perform packet transfer, and reduction in electric power is realized.