## 3 Proposed Design  
FROG-MAC is specifically designed to facilitate the WSN and IoT applications based on heterogeneous traffic. As previously described, for the situations where the emergency traffic could not be delivered in time, the major purpose of WSN deployment could be negatively affected and the required operation could either never take place or be delayed. Another issue found in the previous protocols was that they kept the channel reserved for high priority traffic which could result in resource wastage. The proposed protocol FROG-MAC sends the low priority data in fragments with pauses in between in order to facilitate the emergency traffic. In case some other nodes within the range generate high priority data, they could immediately transmit benefiting from the pauses between the fragments of low priority data. In comparison, the high priority data is not fragmented, and the complete packet is sent at once. Therefore, FROG-MAC would offer the opportunity to emergency traffic for immediate delivery even if the low priority traffic was transmitting. In addition, FROG-MAG resolves the issue of resource wastage as well by scheduling the transmission of low priority traffic when the channel is available, instead of keeping the channel reserved for high priority data. For illustration of the FROG-MAC design, two types of traffic have been assumed, where one depicted regular traffic (low priority) and the other has been used for demonstrating the emergency traffic (high priority). For illustrating the low priority or regular traffic, traffic of Type \(T_{1}\) with Priority \(P_{1}\) has been assumed, which is modeled as CBR traffic with high data rate. In contrast, for the high priority, type \(T_{2}\) with Priority \(P_{2}\) has been used which has Poisson arrivals and a lower data rate. These traffic distributions have been assumed due to the fact that emergency packets are less likely to be generated, and also whenever they would be generated, they would not have a regular pattern; similar assumptions have been found in the previous work [8]. The design of FROG-MAC has been illustrated by Figure 1, where it has been assumed that node 1 transmits low priority (\(T_{1}\)) traffic, whereas node 2 is shown to transmit high priority (\(T_{2}\)) traffic to a common sink (node S). Furthermore, it has been assumed that communication has been established between the transmitted nodes and sink using some handshaking mechanism; RTS/CTS (handshaking) mechanism is out of scope for this discussion. As shown in Figure 1, node 1 begins the transmission process by performing carrier sensing for a checking period \(T_{\text{CH}}\). Upon finding the channel idle, it performs back off and then begins transmission of its low priority packet in fragments after establishing the communication using some handshaking scheme. The size of each fragment is S\({}_{\text{FRAG}}\) (bytes) and duration of each fragment is \(T_{\text{FRAG}}\). Between two consecutive fragments, an interval 'interruptible period' \(T_{INT}\) is assumed in order to enable the node with high priority traffic to access the medium. In case no high priority data is  
Figure 1: FROG-MAC Design. generated between this period, all the pending fragments of low priority would transmit. When high priority data is generated at some node, it performs carrier sense for 'checking period' \(T_{CH}\) (\(T_{CH}<T_{INT}\)); if the channel is found to be idle, it performs back-off and transmit. On the other hand, if a node with high priority data does not find the channel idle during \(T_{CH}\), it continues to listen to the channel and transmits as soon as the channel becomes available (this case has been illustrated in Figure 1). It is to be noted that high priority data is not fragmented and is sent as a single unit. At present, low and high priority data are not separately stored; hence, all the fragments of low priority data which had been transmitted prior to the channel interruption by high priority data are retransmitted once the channel becomes available.