# On Cross-Layer Interactions for Congestion Control in the Internet
## 5 Performance Evaluation
### Access Link, Common TCP  
The second simulation group was supposed to verify the performance and interactions in a more common scenario with a different delay set to each link, representing the access link connecting an institution to an Internet Service Provider (ISP) [17]. The results are gathered in the following tables. Table 6 presents the quartiles of single flows' throughput. Table 7 compares [PERSON]'s index (RTT-fairness) for all flows. Table 8 gives the average queue size with its standard deviation, and Table 9 shows the packet drop ratio. Introducing the varied RTT did not change the overall throughput. This is because neither the AQM algorithm nor the TCP version influences the bandwidth utilization, which is approximately 93-95%. It also implies that the average throughput of TCP connections is comparable in all cases. However, the throughputs of particular flows are significantly different. It is visible when we compare the quartiles of single flows' throughput (Table 6) and [PERSON]'s index (Table 7). Varied RTT highly influences how the bandwidth is shared among all long-lived flows. In the analogous DC scenario, all evaluated TCPs combined with both AQMs, provide very high fairness ([PERSON]'s index around 1); in this scenario, especially in uncongested and mildly congested networks, achieving even close results proved unattainable. In the uncongested and mildly congested network, the worst results in terms of equal bandwidth sharing are observed for two interactions, i.e., New Reno and Cubic with DT; the median throughput is far below the average, the Jain's index is also low. Moreover, New Reno, even with PIE or CoDel, does not provide satisfactory results in terms of RTT-fairness. Similarly, as in the DC scenario with common TCPs (see Section 5.1), the C-TCP and DT combination yields the highest RTT-fairness. Note that Cubic, especially in the mildly congested network, benefits the most from replacing DT with PIE or CoDel. TCP Cubic \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**DT**} & **PIE** & **CoDel** \\ \hline \multirow{3}{*}{UC} & New Reno & 2.74/5.50/14.26 & 5.41/6.51/12.83 & 4.79/6.80/13.98 \\ \cline{2-5}  & Cubic & 4.78/9.25/16.48 & 7.34/8.62/11.68 & 6.85/9.63/12.70 \\ \cline{2-5}  & C-TCP & 8.28/10.63/11.64 & 5.67/10.93/14.88 & 6.31/11.57/13.42 \\ \hline \multirow{3}{*}{MC} & New Reno & 0.53/0.78/1.06 & 0.48/0.70/1.20 & 0.52/0.74/1.17 \\ \cline{2-5}  & Cubic & 0.00/0.01/1.93 & 0.68/0.82/1.14 & 0.72/0.90/1.16 \\ \cline{2-5}  & C-TCP & 0.56/0.96/1.32 & 0.47/0.67/1.19 & 0.51/0.71/1.15 \\ \hline \multirow{3}{*}{HC} & New Reno & 0.05/0.07/0.12 & 0.08/0.10/0.13 & 0.08/0.10/0.12 \\ \cline{2-5}  & Cubic & 0.05/0.09/0.13 & 0.08/0.09/0.13 & 0.08/0.10/0.12 \\ \cline{2-5}  & C-TCP & 0.06/0.08/0.12 & 0.08/0.10/0.13 & 0.08/0.10/0.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Quartiles of flows’ throughput [Mpps] in the Access Link scenario with common TCPs, UC—uncongested, MC—mildly congested, HC—heavily congested network. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**DT**} & **PIE** & **CoDel** \\ \hline \multirow{3}{*}{UC} & New Reno & 0.41 & 0.59 & 0.61 \\ \cline{2-5}  & Cubic & 0.69 & 0.86 & 0.84 \\ \cline{2-5}  & C-TCP & 0.94 & 0.82 & 0.89 \\ \hline \multirow{3}{*}{MC} & New Reno & 0.54 & 0.61 & 0.65 \\ \cline{2-5}  & Cubic & 0.24 & 0.76 & 0.80 \\ \cline{2-5}  & C-TCP & 0.78 & 0.59 & 0.62 \\ \hline \multirow{3}{*}{HC} & New Reno & 0.60 & 0.87 & 0.90 \\ \cline{2-5}  & Cubic & 0.65 & 0.87 & 0.91 \\ \cline{2-5}  & C-TCP & 0.68 & 0.89 & 0.91 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: [PERSON]’s index (fairness) among long-lived flows in the Access Link scenario with common TCPs, UC–uncongested, MC—mildly congested, HC—heavily congested network. preserves higher fairness than the other two protocols because the congestion window growth function is independent of RTT. In a heavily congested network, the fairness provided by any TCP combined with PIE or CoDel is significantly better than in combination with DT.