FIGS. 8A-8E show the operation of the link promotion method of the present invention where FIG. 8A is a flow chart showing an example of detailed steps of processing the promoted links and associated links corresponding to the steps 112 and 113 in FIG. 6A to build a final route, and FIGS. 8B-8E are diagrams corresponding to that of FIGS. 2B and 6B-6D to show how the final route is built via the pr