# mmS-TCP: Scalable TCP for Improving Throughput and Fairness in 5G mmWave Networks
## 4 Evaluations
### End-To-End Throughput of Single Flow  
Although S-TCP can provide sufficient throughput in mmWave links, it can generate many duplicated ACKs and cause fairness issues for other CCAs. In the mmS-TCP proposed in this study, the cwnd increase mechanism was changed, and a gentler cwnd increase than in S-TCP might have affected throughput. Therefore, we evaluated whether mmS-TCP could guarantee sufficient average throughput, and we compared average throughput of existing CCAs together. The average throughput of a single TCP flow was evaluated for three scenarios, and the optimal delivery rate for each scenario is displayed at the top in Figure 10.  
In Scenario 1, where one instantaneous outage occurs, CUBIC TCP performed a total of two cwnd reductions in the initial stage of congestion avoidance and in the outage event. Thereafter, due to the slow increase in the congestion avoidance phase, the average throughput was about 808 Mbps. HS-TCP caused many duplicated ACKs in slowstart phase and decreased cwnd by a larger margin in the outage event due to the aggressive cwnd increase. This resulted in lower average throughput than CUBIC. H-TCP showed a relatively significant cwnd decrease and a slow cwnd increase in the congestion avoidance, and H-TCP took a long time to increase after RTO occurred in the outage event and cwnd decreased to 1. The Yeah algorithm stayed in congestion avoidance until the 15 s time mark, did not reach the maximum available capacity, and showed low average throughput due to the very slow cwnd increase mechanism. S-TCP and mmS-TCP occupied the available  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \multicolumn{2}{c}{\begin{tabular}{c} **Scenario 1** \\ \end{tabular} } & \multicolumn{2}{c}{**Scenario 2**} & \multicolumn{2}{c}{**Scenario 3**} \\ \hline  & \begin{tabular}{c} **Total Dup.** \\ **ACKs/Total** \\ **Packets** \\ \end{tabular} & \begin{tabular}{c} **Dup. ACKs** \\ **(\(\leq\)3.0 s)/Total** \\ **Packets** \\ \end{tabular} & \begin{tabular}{c} **Total Dup.** \\ **ACKs/Total** \\ **ACKs** \\ \end{tabular} & \begin{tabular}{c} **Dup. ACKs** \\ **(\(\leq\)3.0 s)/Total** \\ **Packets** \\ \end{tabular} & \
\begin{tabular}{c} **Total Dup.** \\ **ACKs/Total** \\ **Packets** \\ \end{tabular} &
\begin{tabular}{c} **Dup. ACKs** \\ **ACKs/Total** \\ **Packets** \\ \end{tabular} \\ \hline S-TCP & 9.7\% & 6.4\% & 11.4\% & 7.4\% & 11.5\% & 7.5\% \\ \hline mmS-TCP & 5.0\% & 1.8\% & 5.8\% & 2.3\% & 6.1\% & 2.6\% \\ \hline CUBIC & 0.56\% & 0.35\% & 1.92\% & 0.84\% & 2.23\% & 1.35\% \\ \hline HS-TCP & 4.65\% & 3.82\% & 7.66\% & 6.63\% & 10.26\% & 8.84\% \\ \hline H-TCP & 2.97\% & 2.22\% & 3.65\% & 3.1\% & 3.32\% & 2.74\% \\ \hline Yeah & 0.13\% & 0.13\% & 0.19\% & 0.19\% & 0.67\% & 0.32\% \\ \hline \end{tabular}  
Notes: Dup. ACKs: duplicated acknowledgements; S-TCP: scalable TCP; mmS-TCP: scalable TCP for mmWave; HS-TCP: highspeed TCP; H-TCP: Hamilton TCP; TCP: transmission control protocol.  
\end{table}
Table 2: Comparisons of the rate of duplicated ACKs to total packet.  
Figure 10: Comparisons of average throughput according to the scenarios and TCP CCAs.  
bandwidth more efficiently than the existing CCAs, and even when RTO occurred in an outage event, high average throughput was secured with a rapid increase in cwnd.  
The average throughput of all CCAs decreased in Scenarios 2 and 3, where multiple large and small NLoS transmissions occurred. However, S-TCP and mmS-TCP had the smallest average throughput reduction. Although there was a difference in average throughput between S-TCP and mmS-TCP depending on the scenario, both congestion controls ensured average throughput of about 80% or more of the available capacity. None of the remaining CCAs provided sufficient average throughput due to repeated slow congestion avoidance after reducing cwnd with frequent NLoS events.