## 5 Simulation and Performance Analysis
### Migration Algorithm Performance Evaluation
From the figure, it can be seen that the total migration cost of the system increased as the node size increased; the RT algorithm had a higher total migration cost than other algorithms because of its higher computational complexity. However, with the precomputation process included, the system's overall migration cost was considerably less than that of the other two basic approaches. From Figure 6, it can be seen that the number of migrations per unit time of the system increased with the increase in the number of nodes. Compared with the other two algorithms, the number of migrations was significantly reduced by the RT algorithm. Comparing the RT algorithm with the fixed weight algorithm, it can be concluded that the sensing of the RAIL algorithm can effectively reduce the number of migrations. Comparing the RT algorithm with the simple instant algorithm, it was found that the multi-objective decision-making of TOPSIS could effectively reduce the number of migrations. Figure 7 shows the average resource occupancy of the destination nodes when the RT algorithm and the simple instant algorithm were used to select the destination nodes for migration. This figure shows that for various numbers of nodes, the RT method used less of the destination node's resources, on average, compared to the simple instantaneous approach. Figure 8 shows the single migration cost of a VNF under different algorithms. From the figure, it can be seen that the single migration cost based on the RT algorithm was significantly higher than that of other algorithms because of its higher migration overhead and lower number of migrations. In summary, the RT algorithm can effectively reduce the number of migrations and achieve more efficient network balancing, but it brings higher computational complexity and increases the migration computation time, resulting in higher single migration costs. To retain the advantages of the RT algorithm and reduce the migration computation time, we propose the RAIL&TOPSIS algorithm (PRT algorithm) with the collaboration of precomputation and real-time computation by adding the precomputation mechanism to the RT algorithm. Figure 5 shows that following the addition of precomputation, a significant reduction was achieved in the system's overall migration costs, which were lower than those of the fixed weight algorithm and the simple instantaneous algorithm. Figure 8 shows a comparison between the PRT algorithm and the RT algorithm, which effectively lowered the cost of a single migration to levels s lower than those of the other two baseline methods. Because the number of migrations was the same as that of the RT \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Algorithm** & **Similarities with RT Algorithm** & **Differences from the RT Algorithm** & **Expected Benefits** \\ \hline RT algorithm & — & — & Obtaining the best migration solution under the optimization goal, but the complexity of the migration calculation is too high. \\ (RAIL\&TOPSIS) & — & — & \\ \hline \multirow{3}{*}{Fixed weight algorithm} & The best destination node is selected using TOPSIS & The VNF to be migrated is chosen to be legacy and not resource-aware. & Reduces computational complexity to some extent, but does not speed up node recovery rate. \\ \cline{2-4}  & VNFs to be migrated are chosen to adopt RAIL for resource awareness. & The destination node is selected using the performance constraints that are satisfied by that node. & Reduces the computational complexity of migration, but increases the number of migrations and reduces the stability of the system. \\ \hline \multirow{3}{*}{PRT algorithm} & The RAIL and TOPSIS algorithms are also used. & Incorporates a pre-computation mechanism into the migration process to speed up the rate of migration. & Greatly reduces the overhead of real-time migration calculations during migration. \\ \cline{1-1} \cline{2-4}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of Algorithmic Similarities, Differences and Expected Benefits.