1 are used in this connection a bi directional path is set in the inner physical link 3 1 and in the outer physical link 3 2 respectively thereby redundant paths can be set to mutual addresses in other words paths 4 01 a and 4 10 a are set in the outer physical link 3 1 and paths 4 01 b and 4 10 b are set in the inner physical link 3 2 respectively when the number of dkcs 1 increases to 9 and over to 13 excluded gsw 2 3 is connected to gsw 2 0 and gsw 2 1 additionally in this connection for the connection between adjacent gsw 2 1 and gsw 2 2 a bi directional path is set in each of the inner physical link 3 3 and the outer physical link 3 4 thereby redundant paths are set to the mutual addresses fig9 shows how a path is set for the connection between diagonal gsw 2 0 and gsw 2 2 in other words for the connection from gsw 2 0 to gsw 2 2 a path 4 02 c is set in each of the outer physical links 3 1 and 3 3 and another path 4 02 b is set in the diagonal physical link 3 9 and for the connection from gsw 2 2 to gsw 2 0 a path 4 20 a is set in each of the inner physical links 3 2 and 3 4 and another path 4 20 b is set in the diagonal physical link 3 9 thereby redundant paths are set to the mutual addresses the paths 4 02 c and 4 20 b may be set oppositely to.