# A Novel Covert Channel for IEEE 802.11 Networks Utilizing MAC Address Randomization
## 7 Scenario 3--Covert Channel with Sliding Window Protocol  
We conducted an analysis of the covert channel performance by varying the window size from 1 to 100,000. The parameters used are consistent with those listed in Table 1, and a regular 10 ms transmission interval was maintained throughout the experiments. In isolated scenarios, as anticipated, we found that the window size did not impact the throughput, which remained constant (see Figure 16). This observation aligns with the results obtained from the previous two scenarios. However, the effect of the SWP became noticeable as more stations joined the network. For instance, when an additional 10 stations were introduced, we observed that increasing the window size led to a corresponding increase in throughput, eventually reaching a point of saturation.  
The advantages of employing SWP became even more evident in dense environments, where the number of stations ranged from 30 to 50. Comparing these results to those shown in Figure 11, we noticed a significant average improvement of 1.45 Kbps in the throughput. The pattern remained consistent: as more stations associated with the BSS, we observed a linear and proportional relationship between the throughput and window size until saturation.  
The results clearly demonstrated that employing SWP effectively mitigated the impact of the increased station count and their respective offered loads, leading to a substantial improvement in throughput. This improvement became particularly evident when using larger window sizes, as it resulted in a constant throughput. The underlying reason for this observation is that, with small window size, the transmission window fills up quickly, thereby reducing transmission opportunities. Contrariwise, as the window size increases, more frames can be transmitted before awaiting acknowledgment, enabling the STA to send more frames than possible with the mechanisms employed in the previous scenarios.  
Figure 17 clearly demonstrates the unpaired frame efficiency provided by SWP. When comparing these results with those shown in Figure 12, it becomes evident that increasing the number of stations leads to more frame losses, even with retransmission. In fact, in scenarios involving external traffic, it was observed that no efficiency above 90% was achieved, except for the isolated scenario. However, when employing SWP, the frame efficiency consistently reached 90% or higher across all scenarios. Focusing specifically on congested environments, such as those with 40 and 50 stations, notable efficiency gainsof 30% and 31%, respectively, were observed compared to the previous scenario. This highlights the significant advantages of utilizing SWP in improving frame efficiency.  
The utilization of SWP significantly altered the dynamics of frames within the covert channel as evidenced by the data presented in Figures 18 and 19, showcasing the delay and jitter, respectively. It was observed that delay and jitter are directly proportional to the window size: smaller window sizes resulted in reduced delay and jitter, while larger windows led to increased delay and jitter. When comparing these results with those shown in Figures 13 and 14, specifically in scenarios involving external traffic with 10 to 50 additional stations, it is worth noting that no delays exceeding 1 ms were observed. In densely populated environments, such as those with 30, 40, and 50 additional stations, there was an average reduction in delay of 4.2 ms and a decrease in jitter of 3.8 ms when compared to the previous scenario.  
These findings highlight the positive impact of SWP on mitigating delay and jitter, resulting in more efficient and reliable frame transmission within the covert channel.  
Figure 16: Covert channel throughput after the adoption of sliding window protocol.  
Figure 17: Covert channel efficiency after the adoption of sliding window protocol.