# Estimating PQoS of Video Conferencing on Wi-Fi Networks Using Machine Learning
## 4 Discussion
Therefore, presenting 802.11 network performance parameters as a decision tree model facilitated identifying any change in key parameters affecting the perceived quality of video conferencing calls over Wi-Fi networks. For example, the REPTree model trained with the 802.11 ax 2.4 GHz (2 ax) dataset was analyzed to showcase how 802.11-specific network performance parameters used in the tree model can correlate to any wireless quality degradation scenario. Indeed, operational teams can infer the root causes of any wireless quality degradation by correlating the changes that occurred within individual 802.11 network performance parameters to wireless conditions. Figure 5 shows the tree model produced by the REPTree algorithm trained with the 2 ax dataset to estimate the perceived quality of video conferencing on Wi-Fi networks; the depth of the tree has been limited to five leaves so that it can be presentable in this article. Furthermore, the received signal strength indicator (RSSI) was selected as the root of the tree with the threshold of \(-\)68.5 dBm. RSSI is one of the most commonly used parameters for analyzing the quality of wireless communication. Although RSSI has been commonly used for quality assessment, different devices can report considerably different  
Figure 5: Tree model for REPTree trained with 2 ax dataset to classify wireless quality into MOS classes. RSSI values in the same location because the IEEE has not yet standardized the correlation between RSSI and received signal strength (RSS). This study used different devices from different vendors to reduce the probability of RSSI overfitting during the training phase. The Zyxel 5501 AP was equipped with 4 \(\times\) 4 multi-input, multi-output (MIMO) antennas for the 2.4 GHz interface. Therefore, it was expected to see different RSSI thresholds in the REPTree model for antenna numbers one and three during beamforming. The txprshort represents the number of short preambles transmitted. The preamble synchronizes various timers between the transmitter and receiver, while the receiver uses the preamble to lock to the signal and select a suitable antenna. The short preambles can be transmitted only with 2 Mbps, 5.5 Mbps, and 11 Mbps speeds. When a collision occurs, the AP sends a new frame with a new preamble so that the receiver can synchronize again. An excessive number of short preambles can indicate poor channel quality, likely due to collisions. The d11_txmulti and rxdtmcast represent the number of transmitted multicast frames and the number of received multicast data frames, respectively. The multicast traffic in 802.11 should maximize the number of receivers, and therefore the multicast transmitter uses much lower data rates with sufficient power levels to reach the farthest clients. Hence, a higher number of multicast frames will result in lower transmission speeds and greater airtime usage so that the capacity of a Wi-Fi network will decrease considerably. Therefore, even with 802.11 ax technology, wireless clients participating in video conferencing can experience capacity limitations due to a high number of multicast frames. On the other hand, the rxdsucastmbss represents the number of received data frames with good frame check sequence (FCS) and matching receiver address in the mesh basic service set. In effect, a high number of multicast packets, compared with unicast packets in the 802.11 ax 2.4 GHz (2 ax) dataset, can indicate a capacity limitation on the Wi-Fi network. The rxnodelim represents the number of delimiters that are not valid in a received aggregated media access control protocol data unit (MPDU), whereas the rxcsplitch confirms that the preamble is correct, although it cannot correspond to the header in the received frame. These counters will increase when the received frame contains cyclic-redundancy check (CRC) errors, and necessary fields cannot be extracted from the frame.