# Situation-Aware Survivable Network Design for Tactical Environments
## 4 Performance Evaluation
### Situational Backoff Reset Algorithm  
We conduct a simulation using Riverbed modeler, known as OPNET simulator [31] and set the simulation parameters as shown in Table 2. As previously mentioned, we consider three service classes, namely, voice, multimedia conferencing, and short messaging. In the simulation, voice traffic represents C2; therefore it is assigned high-priority. Video surveillance traffic is mapped to middle-priority, and data traffic, such as short messages and low-resolution images are considered low-priority. For the tactical wireless network setup, the IEEE 802.11e protocol, 1 Mbps data rate, and AODV routing protocol are used. Figure 8 shows the node configuration for that tactical network simulation. The total 15 nodes include 1 gateway node, 2 high-priority traffic, and 3 middle-priority traffic, while the rest are low-priority traffic and are distributed in an 800 m by 400 m field. Figure 6: Routing path construction with the proposed routing algorithm. Figure 7: Path repair process with the proposed routing algorithm. Figure 9a,b compares the performance of high-priority traffic for the conventional protocol and the proposed algorithm. In each figure, the blue dots show the performance of the conventional protocol, and the red dots show that of the proposed algorithm. In Figure 9a, the end-to-end delay of voice traffic is presented. With the conventional protocol, a large delay is observed occasionally, while the proposed algorithm maintains small latency because the proposed algorithm can provide absolute priority for high-priority traffic. Considering that the service performance objective for the voice is 220 ms and 250 ms, as seen in Table 1, the conventional protocol does not guarantee MQoS of the voice traffic while the proposed algorithm does. To evaluate voice traffic more clearly, we introduce the mean opinion score (MOS) [32], which is a metric related to the quality of experience (QoE), which is shown in Figure 9b. The MOS represents a quality satisfaction level from 5 to 1, and the meaning of the score is excellent, good, fair, poor, and bad in descending order. In the case of the conventional protocol, the MOS value is 4 at first; however, it decreases shortly to 1 and fails to recover in poor quality level. However, the proposed algorithm is verified to provide guarantee of absolute priority to voice traffic by maintaining an MOS value to good quality level. As for voice traffic, we measure the end-to-end delay of a video surveillance application, as shown in Figure 10. The performance requirement for video defined by the U.S. Army UC RA is 220 ms. A node transmits video traffic during 60 s at 2 min and 40 s in simulation time. In the case of the conventional protocol, the end-to-end delay increases to 3.5 s between 190 s and 200 s, the time when the voice application is also activated in simulation time. However, the performance of the proposed algorithm does not degrade because it can avoid collisions between low-priority and higher priority traffic. Such a long \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameters** & **Value** \\ \hline Simulator & OPNET 18.7 \\ Simulation time & 300 s \\ Number of nodes & 15 \\ Routing protocol & AODV \\ High & VoIP G.723.1 \\ Traffic type & Middle & Video conferencing (10 frame/s) \\ Low & Short message (1000 byte/s) \\ MAC protocol & 802.11e EDCA \\ Data rate & 1 Mbps \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters setup. Figure 8: Node configuration in OPNET. end-to-end delay as observed in voice traffic means the conventional protocol not only fails to distinguish the priority of tactical applications but also do not meet the requirements. Contrary to the poor performance of the conventional protocol, the proposed algorithm can handle video traffic without a delay problem. Finally, we evaluate the throughput performance for a short message application and the total application as presented in Figure 11. Figure 11a compares the throughput of a short message, which corresponds to low-priority traffic.