# MPResiSDN: Multipath Resilient Routing Scheme for SDN-Enabled Smart Cities Networks
## 6 Results and Discussion
### Storm Challenges  
Here, we look at the results of evaluating the four schemes under the storm challenge model, using the four performance metrics. Figure 13(a) shows the actual throughput produced by the schemes under the storm challenge, which is modeled in Figure 10. The throughputs for all four schemes are at their highest values in the first 10 s because the storm has not yet started. From \(t=10\) to \(t=20\), the storm began to affect path 2, which is used by \(\text{MPResiSDN}(k=2)\) and \(\text{MPResiSDN}(k=3)\). The storm challenge increases noise, which affects the sensor nodes impacted by the storm. This is reflected in a slight effect on the throughput of both \(\text{MPResiSDN}(k=2)\) and \(\text{MPResiSDN}(k=3)\). At this time, the SpanningTree and MPResiSDN(\(k=1\)) are not affected because they use path 1, which is not yet covered by the storm challenge. The worst damage caused by the storm challenge occurs from \(t=20\) to \(t=49\). Although path 2 is freed as the storm moves away, it begins to affect both paths 1 and 3. As path 1 is the only path used by MPResiSDN(\(k=1\)) and Spanning Tree, the throughput dramatically decreases at that time. However, MPResiSDN(\(k=2\)) and MPResiSDN(\(k=3\)) can successfully handle the challenge because they can use an alternative path. As shown in Figure 13(a), the throughput produced by the MPResiSDN(\(k=2\)) and MPResiSDN(\(k=3\)) schemes is reduced; however, they still maintain an acceptable level of performance. At \(t=50\), the storm begins to leave the affected area. As the storm leaves, no paths are affected. This is immediately reflected by an increase in the actual throughput of the MPResiSDN(\(k=2\)) and MPResiSDN(\(k=3\)) schemes. MPResiSDN(\(k=1\)) takes longer to recover and the Spanning Tree scheme takes even more time. The evaluation results for the four schemes under the storm challenge using the goodput performance metric are shown in Figure 13(b). Initially, goodput is not affected by the storm challenge as the challenge has not affected a wide area. When the challenge affects a larger area and covers more paths, the goodput of the MPResiSDN(\(k=1\)) and Spanning Tree schemes drops dramatically because these schemes do not use alternative paths. MPResiSDN(\(k=2\)) and MPResiSDN(\(k=3\)) schemes can handle the challenge and maintain approximately the same level of goodput. They are not affected by the storm challenge because they always have alternative paths to use. When the storm starts to leave the area, the single path used by MPResiSDN(\(k=1\)) and Spanning Tree becomes available. Thus, these schemes start to work again. Note that the Spanning Tree scheme requires more time to recover from the challenge. The results of evaluating the four schemes under the storm challenge using the overhead metric are shown in Figure 13(c). In the first 10 s, the overhead results under the storm challenge are similar to those under normal operation because the storm has not  
Figure 14: Comparison of the four strategies under the storm challenge. started yet. From \(t=10\) to \(t=19\), the storm starts to cover path 2, resulting in noise that affects communication from and to the sensor nodes on the path. The noise slightly reduces the overhead of MPResiSDN(\(k=2\)) and MPResiSDN(\(k=3\)) schemes because it causes dropped packets on path 2. However, packets on path 2 are all duplicates; therefore, dropping some of them reduces overhead rather than goodput. The goodput is not affected for paths 1 and 3 because they are both completely out of the challenge. Spanning Tree and MPResiSDN(\(k=1\)) schemes are not affected at this time because path 1 is free. From \(t=20\) to \(t=49\), the storm challenge moves away. Path 2 is no longer affected by the storm. However, path 1 and path 3 are affected. This is reflected in a decrease in the overhead of MPResiSDN(\(k=2\)) and MPResiSDN(\(k=3\)) in the same manner that has been described previously.