## 4 Implementation Details
### Generating Heterogeneous Arrivals
Traffic of type-1 (\(T_{1}\)) was generated at Constant-Bit Rate (CBR) to represent the periodic monitoring applications of IoT. On the other hand, Type-2 (\(T_{2}\)) traffic was generated at exponentially distributed inter arrival periods (Poisson arrivals) to depict the emergency traffic. The traffic modeling has been done based on assumptions made in [17]. The packet size of both \(T_{1}\) & \(T_{2}\) traffic was assumed to be same, whereas the average arrival rate of \(T_{2}\) has been considered lower as compared to that of \(T_{1}\). The parameters of packet size and transmission time have been assumed based on existing implementations of SCP-MAC [32] & ADP-MAC [33]. Also, the different packet arrival rates of two traffic types have been selected based on the assumptions made in previous literature [22; 23]. Table 2 summarizes the experimental settings. \begin{table}
\begin{tabular}{c c} \hline \hline
**Simulation Parameters** & **Value** \\ \hline Simulation Duration & 6000 s \\ Number of iterations for each result & 50 \\ Transmission Bit Rate & 20 kbps \\ Number of nodes & 100 \\ Priority levels & 2 \\ Message generation interval for \(T_{1}\) & 60 s \\ Message generation interval for \(T_{2}\) & 120 s (Mean of the exponential distribution) \\ Packet Size (for both types) & 60B, 120B, 180B, 240B, 300B \\ Time taken to transmit each byte (Packetization delay) & 0.4 ms \\ Interruptible Period \(T_{INT}\) & 0.4 ms \\ Checking Period \(T_{CH}\) & Random value (<0.4 ms) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental Settings. Figure 2: Topology Settings. ## 6 Results and Discussion

This section presents the analysis of delay and PDR results for all the cases studied, i.e., First Come First Serve, Prioritization without Fragmentation and finally, Prioritization using Fragmentation. ### First Come First Serve (FCFS)

To begin the experimental study, the delay for both traffic types was investigated without assigning priorities. In this scheme, as soon as a packet is generated, it is transmitted subject to availability of the channel, regardless of the packet type. The delay has been computed by summing up packetization and queuing delays. Packetization delay refers to the time taken by a packet to be transmitted once it gets access to the medium. On the other hand, the queuing delay refers to the delay faced by the packet within the node while waiting for the channel; a simplified global queue has been assumed to monitor the status of packets present in each node. Hence, if there is an earlier generated packet ready for transmission at node 1, the packet which is generated later at node 2 would have to wait until the previous packet of node 1 gets transmitted. Using the experimental settings shown in Table 2, the results shown in Figure 3 were obtained. Packet size was varied from 60B to 300B with increment of 60B and the maximum delay faced by CBR traffic \(T_{1}\), and Poisson traffic \(T_{2}\) has been shown. In the figure, the trend of delay is seen to be increasing with the increasing packet size. As the packet size increases, the packetization delay increases; at the same time, the queuing delay also increases as the packets must wait longer for the ongoing transmissions to get complete. The overlap for delay of both traffic types is clearly visible in Figure 3. Hence, when no priority is implemented, no difference in delay is seen for the emergency and normal traffic. In addition, the PDR was also analyzed for the varying packet lengths. As illustrated by Figure 4, the PDR increases for both traffic types with the increasing packet size. The rationale behind this trend is that in case a longer packet is being transmitted, the packets in the queue must wait for long which results in increased packet drop. As mentioned above, we have assumed for all PDR results illustrated in this paper that the packets which face delay of 2 s or more are dropped.