Patent ID: 7715709

Claim:
A network system including a plurality of optical switches each having a plurality of ports and being capable of switching optical signal routes in the form of light, each said optical switch comprising: detection means for detecting an optical signal power of an optical signal passing through each port; control means for exchanging information of the detected optical signal power among the optical switches, calculating differences of the optical signal powers between the ports of the adjacent optical switches to each other, and controlling said each port so that a transmission route having a minimum accumulation of the calculated differences is selected from among the plurality of routes on which optical signals are transmitted, wherein the control means transmits and receives the information of the optical power using an extended BPDU format having an additional information field in regard to the transmission condition, being added to the bridge protocol data unit (BPDU) format of the spanning tree protocol (STP), and a tree topology with STP is structured through the port control by the control means.