# Situation-Aware Survivable Network Design for Tactical Environments
## 4 Performance Evaluation
### Situational Backoff Reset Algorithm
Compared to the conventional protocol, low-priority traffic of the proposed algorithm has relatively long channel access time, and less chance to transmit is presumed because it resets backoff when it senses higher-priority transmission. However, contrary to our expectation, the throughput of low-priority traffic in the proposed algorithm is comparable to that of the conventional protocol without severe performance degradation. This may be attributed to the fact that, with the proposed approach, the tactical traffic is distinguished well by prioritization. The conventional protocol supports a relative priority that can intensify congestion among different priorities and increase collisions, consequently. As a result, the proposed algorithm shows better performance for total throughput as seen in Figure 11b. Figure 10: End-to-end delay comparison of video application. Figure 9: Performance comparison of voice application. (**a**) End-to-end delay. (**b**) MOS value. These simulation results are used to compare the performance of the conventional protocol and that of the proposed algorithm according to the simulation time. In addition, we conduct 100 simulations and gather the results to investigate the average performance of the algorithms. The end-to-end delay distribution of voice traffic according to each simulation number is presented in Figure 12. For each simulation number, the end-to-end delay of voice traffic is plotted as a type of box plot; the upper graph is for the conventional protocol, and the lower one is for the proposed algorithm. In certain cases, we can observe a large delay for the conventional protocol, such as 21.78 s in simulation run 68 due to the fact that high-priority traffic exists longer than other simulation runs. In these two simulations, none of the voice packets are received. From these results, we can conclude that the conventional protocol is not appropriate for tactical environments and it fails to meet the required QoS level. On the other hand, however, except some simulation cases, the end-to-end delay of the proposed algorithm is small. We calculate the average delay from every 100 simulations, and the cumulative distribution function (CDF) for the average delay of voice traffic is presented in Figure 13. The vertical red line is the reference line of the service performance objective for voice traffic, 220 ms, as shown in Table 1. In the CDF of the conventional protocol, about 58%  
Figure 11: Throughput performance comparison. (**a**) Short message. (**b**) Total throughput. Figure 12: End-to-end delay distribution of voice traffic of 100 simulations. (**a**) 802.11e EDCA. (**b**) Situational backoff reset algorithm. of the average delay is below the reference line (57 cases of the total 98 cases). From the total 100 simulations, 101,591 voice packets are received by the conventional protocol, and 9190 packets corresponding to around 9% are delayed. However, there is only one case with the proposed algorithm in which the average delay of voice traffic exceeds the reference line. In other words, 99% of the measured average delay is below the reference line. With the proposed algorithm, a total of 126,020 voice packets are received, and the delay of 391 voice packets, 0.3% of the received packets, exceeds 220 ms. Figure 14 shows the end-to-end delay distribution of video traffic, measured from 100 simulations. The box plots of video traffic for the conventional protocol and the proposed algorithm have a similar aspect to the result of voice traffic. In the case of the conventional protocol, the end-to-end delay of video traffic is measured from only 66 cases among 100 simulations. Compared to the voice traffic, there are more cases that fail to receive video traffic because of the congested wireless network condition. On the other hand, the proposed algorithm receives video traffic from the overall simulations.