# On the Evaluation of Complex Networks Designs for an Energy-Efficient IP/WDM Core Network
## 7 Results and Discussion
The results demonstrate that to achieve the best results in energy conservation, targeting energy efficiency in the IP layer to minimize the total number of routers' line cards would be of great interest, as routers' ports are found to be the main contributors of power consumption in the IP over WDM networks (825 W) [15; 20]. In this regard, considering the MILP optimization model described in Section 6, the network power consumption would be minimized by taking advantage of the introduced shortcuts using the redesigned topology interconnection and optimizing the network resources by means of grooming traffic demands on fewer links and putting underutilized router ports on sleep mode. In this work, we have assessed the network power consumption of the redesign NSF topology for different average node's mean degrees (k = 4 and 6) to evaluate its impact on energy conservation of the implemented SWN described in Section 4. As can be observed from Figure 10, with k = 4, energy savings achieved can reach 14.4% as the rewiring probability approaches to 1. The results illustrated in Figure 10 along with topology design for k = 4 in Figure 4, demonstrate that when \(p=0\), the effect on power consumption reduction is minimal; however, as the wiring probability in the \begin{table}
\begin{tabular}{c c} \hline \hline \((d)\) & 80 (km) [15] \\ \hline (u) & 16 [16] \\ \hline (\(B\)) & 40 (Gb/s) [17] \\ \hline (\(P_{RP}\)) & 825 (W) [15] \\ \hline (\(P_{Transponder}\)) & 167 (W) [15] \\ \hline (\(P_{Rcg}\)) & 334 (W) [15] \\ \hline (\(P_{EDFA}\)) & 55 (W) [17] \\ \hline (\(P_{OXC}\)) & 85 (W) [18] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Input parameters. SWN increases, more shortcuts introduced. Shortcuts have an impact on decreasing the average path length (diameter) of the network, as widely distant nodes can be closer and reached with a fewer number of nodes traversed, and hence the result of a significant reduction in energy consumption as the number of network resources utilized (router ports, transponders, EDFAs, optical switches, and regenerators) to support traffic demands between nodes are lowered. Figure 11 illustrates the SWN with k = 6; it is observed that it is possible to further reduce power consumption to 28% if the average nodal degree is increased from 4 to 6. It is also notable that with the increase in k, the network diameter is decreased, and power consumption of the network can be reduced as traffic can be groomed on fewer links and underutilized resources can be put on sleep mode. Figure 12 presents the saving percentages that can be achieved for the different rewiring probability with k = 4 and 6, respectively. SCF and random networks illustrated in Figures 3 and 5, respectively, evaluated using the MILP model described in Section 6 to assess the power consumption and compare with current and SWN NSF networks in order to find out if savings can be achieved. Results demonstrated in Figure 13 illustrate that the random design is not as efficient as the SWN  
Figure 11: IP/WDM power consumption of SWN implementation on NSF network against current NSF topology design with k = 6. Figure 10: IP/WDM power consumption of SWN implementation on NSF network against current NSF topology design with k = 4.  
in energy savings. However, with the SCF savings can reach 13% when compared to the current NSF design. The existence of hubs in the SFN reduces the network diameter and makes 60% of nodes reachable through them. This is due to the fact that the smaller the diameter, the shorter the average path length, the less the number of nodes traversed, the less links and devices used, and the less the power consumed. Random graphs, as depicted in Figures 5 and 6, have a slightly higher average path length than the current SWN. Path length is directly proportional with the network diameter as the larger the network diameter, the longer the path is between any two nodes, which justifies the increase in the power consumption.