## 4 Evaluation
### Results
#### 4.3.3 Results of Experiment 3  
The third experiment was carried out on the topology labelled in green and \"3\" in Figure 2. The source and destination routers were R5 and R10, respectively. The evaluation result is shown in Figure 5a,b and Tables 6, 8 and 9. In Figure 5a, the real-life latencies of paths (R5-7-8-10 and R5-6-8-10) \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(I_{\Delta t}\) & **Data Range** & \(L_{i}(\Delta t)>L_{j}(\Delta t)\) & \(L_{i}(\Delta t)<L_{j}(\Delta t)\) & **True Rate** & **False Rate** \\ \hline  
\hline \hline \end{tabular}
\end{table} 
Table 5: Experiment 2’s evaluation results of the proposed PSI between path R7-8-10 and path R7-9-11-10. are presented with curves in orange (R5-6-8-10) and blue (R5-7-8-10) colors. As indicated before, the current path chosen by OSPF is R5-6-8-10, the orange curve in Figure 5b, and the blue curve is the latency of the backup path R5-7-8-10. The indicator \(I_{\Delta t}\) at each time point is shown as a gray spot in Figure 5a. The parameters chosen in the experiment are shown in Table 3.  
As shown in Figure 5a, the PSI seems unable to reflect the channel changes. According to Table 8, when PSI = 1, only 30% of the latencies are really worse than the backup, and from Figure 7, the **accuracy improvement** of Experiment 3_1 is the lowest, only around 200%. Thus we carried out another experiment, Experiment 3_2, adjusting the **latency consistency sensitivity**\(\theta_{s-}\) from 7 to 6, as shown in Table 3. The precision of the indicator has significantly improved, with the **accuracy improvement** raised to almost 360%, as shown intuitively in Figure 6a,b and in Figure 7. It is evident that the experiment accuracy is very sensitive to the parameter **latency consistency sensitivity**\(\theta_{s+/-}\), and thus customers should adjust it according to the real situation of their own network. However, in Experiment 3_1, the **time interval between path swaps**\(T_{PSI}\) was the highest of all experiments, as shown in Equation (13), which means that, after a PSI change, it can stay stable for 3303 s on average. \[ \begin{array}{l}T_{PSI}=\frac{Total\,Time}{Total\,Num.\,of\,I_{\Delta t}\,Suaps }\times\Delta t\\ =\frac{3303}{5}\times\Delta t=660.6\times 5=3303s\end{array}  \tag{13}\]  
In Experiment 3_2, after the latency differential sensitivity \(\theta_{s-}\) was changed from 7 to 6, the **time interval between path swaps**\(T_{PSI}\) decreased to 1500 s, as shown in Equation (14), but it was still 1500 times larger than the route change time, and thus it is evident that our proposed metric PSI is able to provide a consistent path congestion prediction. \[ \begin{array}{l}T_{PSI}=\frac{Total\,Time}{Total\,Num.\,of\,I_{\Delta t}\,Suaps }\times\Delta t\\ =\frac{3303}{11}\times\Delta t=300.0\times 5=1500s\end{array}  \tag{14}\] \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(I_{\Delta t}\) & **Data Range** & \(L_{i}(\Delta t)>L_{j}(\Delta t)\) & \(L_{i}(\Delta t)<L_{j}(\Delta t)\) & **True Rate** & **False Rate** \\ \hline
0 & 2–928 & 107 & 820 & 88.5\% & 11.5\% \\
1 & 929–1085 & 92 & 79 & 53.8\% & 46.2\% \\
0 & 1086–1125 & 10 & 30 & 75\% & 25\% \\
1 & 1126–2173 & 281 & 767 & 26.8\% & 73.2\% \\
0 & 2174–3303 & 180 & 950 & 84.1\% & 15.9\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Experiment 3_1’s evaluation result of the proposed PSI between path R5-6-8-10 and path R5-7-8-10.