# An Optimization Routing Algorithm Based on Segment Routing in Software-Defined Networks
## 4 Performance Evaluation
### Simulation Results  
Figures 4-6 show a performance comparison of the algorithms when the size of the network is 100 nodes. Figure 4 shows the path costs for SPF, WSP, SWP, MIRA, the Lee algorithm and our proposed two algorithms. The paths cost in the network represents the sum of the consumption of all paths in the corresponding number of requests. The cost of a path obtained by using (11) is the sum of the cost of each link on a path. So, the paths cost depends not only on link utilization but also on the length of the end-to-end path. As shown in Figure 4, the paths cost of the MIRA algorithm is the largest. Because the MIRA algorithm does not consider congestion on non-critical links, large link utilization causes excessive link cost. And the MIRA algorithm avoids the critical links that tend to cause longer paths. The paths cost of SPF is lower than that of MIRA. The SPF usually selects the shortest path, although the algorithm does not consider the remaining bandwidth of the links. SWP and WSP perform better than SPF because they take into account the hop counts as well as the remaining bandwidth of the links. SWP selects the minimum hops path with the largest available \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Selected Path** & **Delay/us** & **Jitter/us** & **Packet Loss Rate/\%** \\ \hline
1 & 6.79 & 28.87 & 0.84 \\
2 & 9.74 & 45.92 & 1.81 \\
3 & 8.96 & 40.24 & 1.44 \\
4 & 8.11 & 37.28 & 1.56 \\
5 & 10.48 & 49.82 & 2.22 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Network link measurement data. bandwidth. WSP selects the largest available bandwidth with the minimum hops paths. SWP has a longer path than WSP. So, the paths cost of the WSP algorithm is less than that of the SWP algorithm. The Lee algorithm takes into account the link criticality and link congestion index. The number of hops of the path is limited. The Lee algorithm performs better than other traditional algorithms, but it does not consider the consumption of the links resource and load balance in the network. Our proposed Algorithm 1 takes the path cost as an optimization goal to achieve the lowest path cost compared to the above five algorithms. The proposed Algorithm 2 makes some improvements in obtaining the global optimal solution and shows the best performance for paths cost. Figure 5 shows the load balance of the network with the seven algorithms. We define the variance of the link utilization on the network as the load balance by using (12). As shown in Figure 5, the performance of SPF for load balance is the worst without considering link utilization. The performance of WSP is better than SPF because WSP selects the path with the largest remaining bandwidth when it has multiple shortest paths. WSP gives priority to the number of hops and SWP gives priority to the residual bandwidth of paths. The performance of SWP is better than WSP in terms of load balance. The main idea of MIRA is to minimize the influence of future nodes to build the link request and thus effectively avoid the congestion of the critical links. The performance of the MIRA algorithm is better than that of SPF, SWP, and WSP. The Lee algorithm considers the link congestion and has a good effect on load balance. Our proposed Algorithm 1 takes load balance as an optimization target and has obtained better performance than the other five algorithms through multiple iterations of the MOPSO algorithm. Our proposed Algorithm 2 finds a better solution and has the best effect by improving the selection mechanism. Figure 6 shows the maximum link utilization of the network for the seven algorithms. The smaller the maximum link utilization, the greater is the remaining bandwidth, and the better the performance is in avoiding congestion. Because the SPF is the shortest path algorithm without considering available bandwidth, it is easy to create link congestion when the traffic in the network gradually increases, so its maximum link utilization is the largest. However, the WSP selects the path with the largest bandwidth among the shortest paths.