# Situation-Aware Survivable Network Design for Tactical Environments
## 3 Proposed Algorithm
### Situational Backoff Reset Algorithm
#### 3.1.2 The Mechanism of the Proposed Algorithm  
A key feature of the situational backoff reset algorithm is illustrated in Figure 1. The basic structure of the proposed algorithm is similar to that of the commercial standard. However, the proposed algorithm has different management strategies for each priority in hierarchical structure compared to the conventional standard. The 802.11e protocol provides best effort service because it gives relative priority, which may lead to priority inversion and collisions between different priority traffic. This structure is insufficient to transmit tactical traffic, and it raises the necessity of a new design that can guarantee appropriate priority and meet the requirements of MQoS.  
The proposed scheme is designed in stepwise order from high-priority to low-priority. In a tactical environment, urgent and important traffic, such as C2 communication, which corresponds to the high-priority, should be guaranteed. To address this challenge, we introduce the absolute priority scheme for high-priority traffic. The AIFS of middle-and low-priority traffic is lengthened to include the contention window size to the AIFS of the high-priority traffic. Under the proposed design, the high-priority traffic is completely excluded from channel access contention with other priority traffic as well as the priority inversion problem. Consequently, high-priority traffic is served first as an absolute priority.  
As the next step to the absolute priority scheme, we propose the situational back-off reset algorithm for the middle-priority traffic. If the middle-priority traffic adopts a differentiation strategy as the absolute priority scheme does, it may obtain advantages from channel access contention but a long deferral time is ineffective, and performance degradation is inevitable. To distinguish between middle- and low-priority traffic, the low-priority traffic resets the current backoff counter when it senses the transmission of a higher priority traffic and the current backoff counter is in the range of a backoff reset zone (BRZ). We use a traffic identification (TID) value in the QoS control field as a trigger of the backoff reset. Figure 2 shows the QoS data frame structure, and the QoS control field is included in the MAC header. Accordingly, any node can access the TID value, even if the received packet is not destined to this node. As described in Algorithm 1, only in the case of a node that has low-priority traffic to transmit, it checks the condition of the TID value from the received packet and whether its current backoff counter is in BRZ or not. If the condition is satisfied, the corresponding node conducts backoff reset to prevent collision and give channel access preference to middle-priority traffic. Otherwise, that node can keep its backoff counter and transmit when it terminates backoff. In summary, the proposed algorithm effectively prioritizes traffic based on the situation-aware information without an undesi  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Granular Service Class** & **End-to-End Delay (ms)** & **End-to-End Packet Loss (\%)** & **End-to-End Delay Jitter (ms)** \\ \hline Short Messaging & 1000 & 0.5 & - \\ Voice (Assured/Non-Assured) & 220/250 & 1/1 & 20/20 \\ Multimedia Conferencing (Voice/Video only) & 220 & 1 & 20 \\ Broadcast Video (Voice/Video only) & 1000 & 0.1 & - \\ Multimedia Streaming (Voice/Video only) & 250 & 1 & 20 \\ Low Latency Data: IM/Chat, Presence & 300 & 1 & - \\ High Throughput Data & 300 & 1 & - \\ \hline \hline \end{tabular}
\end{table}
Table 1: Granular service performance objectives.  
Figure 1: Conceptual comparison of IEEE 802.11e EDCA and proposed algorithm.