## 4 Experimental Evaluation
### Discussions  
We showed the benefits and importance of multilayer measurements using open-source tools from the empirical results of the above three scenarios. Let us summarize the results for the three measurement scenarios. In Scenario 1, we evaluated communication performance by the impact of antenna direction. The results showed no significant differences in communication quality for the impact of antenna direction at a close range, but its performance would depend on the  
Figure 16: RTTs of TCP and UDP communications on two STAs and one AP (Scenario 3). hardware used. In addition, the methodology indicated that if real-time performance is required, it is necessary to check not only throughput, but also jitter and RTT. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**TCP Communication**} & \multicolumn{4}{c}{**UDP Communication**} \\ \cline{3-10}  & & **STA1** & **STA2** & \begin{tabular}{c} **AP** \\ **(STA1)** \\ \end{tabular} & \begin{tabular}{c} **AP** \\ **(STA2)** \\ \end{tabular} & \begin{tabular}{c} **STA1** \\ \end{tabular} & \begin{tabular}{c} **STA2** \\ \end{tabular} & \
\begin{tabular}{c} **AP** \\ **(STA1)** \\ \end{tabular} &
\begin{tabular}{c} **AP** \\ **(STA2)** \\ \end{tabular} \\ \hline M1 & Invalid & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ STA2 = 10 m & Missing & 12 & 1 & 12 & 0 & 2 & 0 & 0 & 0 \\ \hline M2 & Invalid & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ STA2 = 30 m & Missing & 5 & 2 & 2 & 9 & 22 & 0 & 0 & 0 \\ \hline M3 STA2 = 50 m & Invalid & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ \hline M4 & Invalid & Missing & 22 & 1 & 2 & 41 & 67 & 6 & 3 & 2 \\ \hline M4 & Invalid & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ STA2 = 70 m & Missing & 45 & 15 & 3 & 87 & 166 & 128 & 2 & 62 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Invalid RSSI values observed with the _iw_ tool (Scenario 3). Figure 17: RSSI of two STAs and one AP for TCP and UDP communications (Scenario 3). In the results of the wireless network layer, assessing the impact of RSSI variations on the communication quality was difficult, even if AP and STA were at a short distance. On the other hand, we showed that Tx bitrate helps confirm the occurrence of communication quality degradation as a supplemental indicator. Thus, the measurement of Scenario 1 is essential for understanding the quality of communication as a reference value to evaluate the communication performance in Scenarios 2 and 3. Scenario 2 examined the effect of communication distance as an essential evaluation for building a network. It was found that the throughput degrades significantly with increasing distance, even within a short distance of a few tens of meters. It may be reassuring if the throughput required by the application is achieved, but the throughput may already be degraded due to various factors. Consequently, the reference values obtained in Scenario 1 are helpful for the assessment. In addition, if retry or communication failure appears, a significant degradation of communication quality is likely to cause or have caused this. The features of the wireless network layer in Scenario 2 are two types of errors. One error is that the _iw_ result included inaccurate values of 0 in RSSI. The other is that all information about the wireless interface, including Tx bitrates, was not logged. For instance, if the errors appear, we can understand that the communication performance significantly degrades. In addition, checking the Tx bitrate used in the wireless layer is easy to understand. On the other hand, it is difficult to judge the degradation of communication quality from only RSSI. Scenario 3 evaluated the communication quality in a multiterminal environment. The results are only an example, but we found that in TCP communications, an STA with a poor communication link affects the other STAs with a good communication link. On the other hand, in UDP communication, there was no advantage due to the distance to the AP, and the STA that was far from the AP sometimes had better communication quality.