This method includes: judging, for each certain combination of the source and destination nodes, for which the number of time slots to be allocated is equal to or greater than 1, whether or not certain time slots exist that are capable of forming a route from the source node to the destination node by unused links; for each certain combination judged, at the judging, that the certain time slots exist that are capable of forming the route by the unused links, identifying, for each certain time slot, a shortest route among routes formed by the unused links, calculating an evaluation value from the number of hops in the shorted route, an allocated priority associated with a corresponding certain combination and the number of used links in the corresponding certain time slot; and identifying a maximum evaluation value among the evaluation values.