## 4 Performance Evaluation
### Effect on Faults
#### 4.1.2 Results Analysis  
Figure 3 shows the packet loss rate (%) of 5-Mbps UDP packets from H1 to H5 at specific times. In this simulation, links are down at the 4 th second in cases of \"One Link Down (S3-S2)\" and \"Two Links Down (S3-S2 and S5-S1)\". In the case of \"No Link Down without (w/o) RAD\", only one path (S5-S1-S3-S7) is used. During time 0.0-1.0 s, the route set up via the SDN controller is required and thus minimal packet loss (5.7%) occurs. When links on the used path are downed in the SDN system without RAD, 100% of the packets are lost because only one path is used and fault management for rerouting does not exist. In the case of \"No Link Down with RAD\", the RAD traffic engineer distributes traffic on multiple paths that are set up by the cost function, multi-dimensional routing, and load balancing. Thus, even though this is a case of no link down, the trial time in which to find better paths and distribute traffic on paths occurs with only minimal packet loss (average of 10.5%) for 3.0-5.0 s. However, the loss decreases to nearly 0% after this period. In the case of \"One Link Down\", several paths are used (e.g., S5-S1-S3-S7, S5-S1-S4-S7, S5-S2-S3-S7, and S5-S2-S4-S7). If a link S3-S2 is downed at the 4 th second, the fault/anomaly detection submodule of the traffic analyzer detects the fault. Then, the path (S5-S2-S3-S7) is no longer used and RAD redistributes the traffic on the remaining paths. The response time for one link down occur 43.6% for 4.0-5.0 s, but the loss stops after this period. The case of \"Two Links Down\" shows similar results to those of \"One Link Down\" and only a single path (S5-S2-S4-S7) is available. However, the increase in the number of downed links produces a greater loss rate (56.6%). Figure 4 shows the average packet loss for 10 s. Although in the case of \"No Link Down\" with RAD, more packet loss occurs than without RAD, RAD quickly overcomes link down events such that packet loss occurs at a rate of only 4.9% and 5.8% in cases of one and two links down, respectively. However, in the case without RAD, 100% of packets are lost after links of path are downed. Figure 3: Packet loss rate (%) vs. time. Figure 5 shows the transfer delay of 5-Mbps UDP packets from H1 to H5 in milliseconds (ms). Link down events are the same as those in Figure 1. Because of the links downed at the 4 th second, the delays of \"One Link Down\" and \"Two Links Down\" increase during the 4.0-5.0 s period, but the delay decreases again after 5.0 s. The delay in the \"Two Links Down\" case is much greater than the \"One Link Down\" for the 4.0-5.0 s because the former has only a single path after two links are down, whereas the latter has three available paths. Moreover, the \"Two Links Down\" case after the link down event has greater delay than in the other cases. This is because only one link is available and blocked traffic at the 4 th second is transmitted all together after the event. Figure 6 shows the average transfer delay in ms during a period of 10 s. The greater the number of links down, the greater is the transfer delay. However, our RAD requires a reasonable increase in time compared to the original SDN system without RAD, in which all packets cannot be transferred after a link down event. We measure the connection establishment time of TCP packets. We set up a TCP connection trial from H1 to H5 for every 1 s and calculate the average connection established time during a 10-s period. Figure 7 shows that the SDN system without RAD is influenced by the TCP connection establishment time much more during the link down event and for the number of downed links than is the system with RAD under the same conditions. Moreover, the \"Two Links Down\" case without RAD requires more time than does the \"One Link Down\" case without RAD. This is because of the decrease in the number of available links resulting from multiple links down.