## 6 Results and Discussions
### The Impact of High Traffic Load on Client Satisfaction  
This part illustrates the impact of high traffic load on the end-users' perceived QoE under three different topology scales. The same performance comparison and the same video sample utilised under low traffic were applied; however, the bandwidth of the background traffic that is introduced in the three networks using the Iperf tool is increased. \begin{table}
\begin{tabular}{c c c c c c c c} \hline  & **Network Topology** & \multicolumn{2}{c}{**Abilene**} & \multicolumn{2}{c}{**Geant**} & \multicolumn{2}{c}{**Cernet**} \\ \hline  & **Client-Server** & **H5–H1** & **H10–H4** & **H15–H6** & **H18–H9** & **H7–H35** & **H22–H19** \\ \hline
**OSPF-based appraach** & Packets dropped (out of 127,551) & 39 & 73 & 84 & 117 & 128 & 57 \\  & Average packet jitter (in ms) & 0.008 & 0.017 & 0.013 & 0.015 & 0.022 & 0.004 \\ \hline
**RL-based solution** & Packets dropped (out of 127,551) & 45 & 41 & 29 & 1 & 28 & 51 \\  & Average packet jitter (in ms) & 0.010 & 0.015 & 0.018 & 0.017 & 0.008 & 0.019 \\ \hline \end{tabular}
\end{table} 
Table 3: The number of packets dropped and average jitter during video transmission for the low background traffic load under three topologies (includes random client-server from each network topology). Figure 6: Network throughput during video transmission under low traffic loads in three different topologies. (**a**) Abilene; (**b**) Geant; (**c**) Cernet. As the high traffic load operates, the network gets overloaded, which causes traffic flows to exhibit data losses. Nevertheless, SSIM and VMAF results indicate that our proposed solution performs better than the OSPF-based approach despite the user-perceived quality dropping to good under Cernet and Abilene topologies. The results with the middle-scale network shows an excellent user perceived QoE (see Figure 7). In this case, the viewing experience is affected when the network topology increases. DASH video streaming without the RL-based solution reveals a massive decrease in the users' perceived final video quality, and according to the VMAF and SSIM results, Geant and Cerent users display bad quality viewing behaviour as depicted in Figures 7 and 8, respectively. However, it can be seen in Figure 9a that under small-scale network, the end-user perceived fair viewing experience. As observed, the client satisfaction represented by QoE is dropped with both schemes under large-scale network. However, the results suggest that the obtained QoE of end-users increases with the proposed RL-based solution. Figure 8: SSIM values for DASH video under high traffic loads in three different topologies. (**a**) Abilene; (**b**) Geant; (**c**) Cernet. Figure 7: VMAF values for DASH video under high traffic loads in three different topologies. The results in Table 4 show that the RL-based solution produced a low data loss rate for the generated traffic compared to the OSPF-based approach. It is noticeable that the proposed solution draws advantages when applied on small and middle-scale networks; for instance, the generated traffic under the two networks indicated that the OSPF-based approach reported a high loss rate. Hence, the OSPF protocol cannot resolve the network congestion by rerouting the traffic flows. In contrast, the proposed solution showed a dramatic decrease in the loss rate in these networks. Although the RL-based solution offers better performance in terms of data loss rate under Abilene and Geant, however, considering the results in Table 4 OSPF-based approach imposes lower jitter for almost all the traffic between client-server of both networks. In a large-scale network, the results indicate an improvement in both packet loss rate and delay variation. The network throughput under high traffic loads is illustrated in Figure 9. As observed, the video streaming throughput decreases with the OSPF-based approach because the network gets congested and the links are highly experiencing data loss; the throughput value hits a massive drop and reaches even below 1 Mbps under all networks.