Between a first pair of termination nodes, a first current-use packet transmission path and at least one first spare packet transmission path are defined. Between a second pair of termination nodes, a second current-use packet transmission path and at least one second spare packet transmission path are defined. When no network fault occurs, packets are transmitted between the pairs of nodes in a 1:1 transfer mode in which the pairs transfer packets via both current-use packet transmission paths only. When a network fault occurs in the first current-use packet transmission path, both transmissions are switched from a 1:1 transfer mode to a 1+1 transfer mode, in which the first pair of nodes transfer packets by using the first current-use packet transmission path and the first spare packet transmission path, and the second pair transfer packets by using the second current-use packet transmission path and the second spare packet transmission path.