Figure 12, shows betweenness centrality calculated using Eq. ( Note that we can choose centrality betweenness based on hop count or propagation delay, but we chose centrality betweenness based on hop count because we used the routing algorithm based on hop count. Figure 12 gives betweenness centrality of each nodes, and shows that node 5 has the highest betweenness centrality than other node in NSFNET and node 9 has the second highest. In addition, these nodes are considered appropriate as reference nodes since they are connected with four nodes.