# A Novel Self-Forming Virtual Sub-Nets Based Cross-Layer MAC Protocol for Multihop Tactical Network
## 4 Working of Algorithm
It is noted that sub-nets formation, frequency selection, and data slot scheduling do not depend on the FSM model and run on the information available in TRANS_table, built during the control frames transmissions. ## 6 Experiments, Results, and Performance Evaluation

The proposed VSCL-MAC design is evaluated via extensive simulations on a different set of topologies in OMNET++5.4.1 with INET framework 4.6.0. The protocol is simulated for single and multihop communication scenarios. The number of frequencies \(f_{h}\) is assumed to be more than the number of nodes, or almost twice the number of nodes. A random

Figure 16: Finite state machine for control and data transmissions. mobility pattern is considered for nodes, and during protocol execution, speed of nodes is slow. The parameters and their notation are listed in Table 10.

### Simulation Results and Analysis

We derived the proposed VSCL-MAC design performance in terms of call setup delay, control overhead, network throughput, and latency. #### 6.1.1 Call Setup Delay

For call setup delay, we consider the last bit of REQ message sent from the source node until it receives the REQ_ACK message for the REQ. We evaluated call setup delay for 5 to 50 nodes that have data to transmit on different hops. In VSCL-MAC design, the average call setup delay is low as compared to conventional TDMA-based MAC because participating nodes can send combined REQ and REQ_ACK packets, which significantly decreases the call setup time and total number of control frames transmission, as shown in Figure 17, whereas in conventional TDMA-based design, each REQ or ACK packet consumes an individual time slot to be transmitted and increases call set up time linearly with the increase in number of nodes \(N\). In some cases, the call setup delay in the proposed design abbreviates more when the sender of REQ or ACK is the same for most of the transmissions and has the packet available in its queue concurrently. This has a significant impact on average call setup time and also reduces the number of control frames \(L\). In these scenarios, traditional TDMA-based \begin{table}
\begin{tabular}{c c} \hline \hline
**Notation** & **Parameters** \\ \hline \(R_{t}\) & Network data rate \\ \(D\_slots\) & No. of data slots \\ \(L\) & No. of control frames \\ \(f_{h}\) & No. of frequencies \\ \(k\) & No. of hops \\ \(M\) & No. of messages \\ \(S_{c}\) & Size of control slot \\ \(S_{d}\) & Size of data slot \\ \(T\) & TDMA frame duration \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Parameters and their notation. Figure 17: Average call setup delay for VSCL-MAC and TDMA-based MAC design. design consumes many control frames compared to VSCL-MAC, as shown in Figure 18. This substantial increase in \(L\) is not favorable for time-critical tactical applications. We evaluated the call setup time of network topologies when all nodes transmit on the same hop and analyzed the average call setup delay of VSCL-MAC, as shown in Figure 19. For 1-hop transmissions, a total of 2.5 or 3 control frames are consumed. The design is simulated for maximum 4-hop transmission, which merely has 2200 ms on average of call setup delay with a network of 50 nodes and consumes only five control frames. We observed that with \(k\)-hop transmission, the VSCL-MAC protocol consumes \(k\) control frames to set up a call specially when the source node uses its preceding nodes to relay the packet and has a greater MAC ID than the source and relay node(s). This limits slots wastage and reduces call setup delay. Usually, in the last control frame, most source nodes receive ACKs of the REQ messages and the design consumes \(k+1\) rounds of control

Figure 19: Average call setup time with respect to number of hops in VSCL-MAC design. Figure 18: Total control frames transmission time for VSCL-MAC and TDMA-based design. frames. Even in the worst-case scenario with 4-hop transmissions, \(L\) does not exceed more than six control frames and does not decrease bandwidth utilization for data transmission to the lowest range.