REDUNDANT NETWORK SYSTEM

PROBLEM TO BE SOLVED: To provide a network system which is made inexpensive by decreasing the number of repeating lines in comparison with a mesh type network, and secures reliability and defendability. SOLUTION: On a network composed of a plurality of communication nodes A-H and repeating lines connecting these nodes, the respective nodes are connected in the shape of ring and further, significant nodes A and G for a communication specification while having priority in comparison with the other general nodes on the basis of physical conditions (such as a role of a device accommodated in each of nodes or routing protocol of a directly accommodated network) and significant nodes C and E for positioning while improving the priority of general nodes on the basis of geographic conditions (such as the number of general nodes for repetition) are determined and the network is constituted by directly connecting such significant nodes in the shape of mesh.