# Efficient Communication Model for a Smart Parking System with Multiple Data Consumers
## 5 Evaluations
### Simulation Setup  
In the experiments, the BR is the root node of the IPv6 mesh and creates a DODAG with one RPL instance. All the nodes are forwarders that are capable of forwarding data packets in the upward direction toward the root node (BR). The data collator is placed at a one-hop position from the BR so that it lies in the upward path en route to the BR for each node. The BR is connected through SLIP protocol to a laptop. The Firefox browser is used from the laptop to connect to the data collator to access the occupancy data over the Internet. The five networks to be examined are labeled as Top1, Mid1, Dist4, Mid4 and MidAgg as per their communication model. The model named Top1 denotes a network with a single BR and one data collator placed at the top of all the nodes. Mid1 refers to the network with a single BR and one data collator at the center of the network. The third model, Dist4, has the BR at the center, and its four data collators are distributed within the network and are away from the BR. In contrast, Mid4 refers to four data collators that are adjacent to the BR, at the middle of the network. The final MidAgg model denotes a network with four data collators in the center where each node aggregates the occupancy data. The final model is expected to consume less energy, as it reduces the total number of occupancy data packets transmitted in the network.  
The grid network is considered for simulation, as the results are comparable across multiple studies. The channel check rate for a node is kept at 8 HZ so as to reduce the power consumption of the nodes. A radio duty cycling ensures that the nodes remain in sleep mode for as long as possible. The data collators do not participate in radio duty cycling to ensure high reliability. The simulation parameters are summarized in Table 1.  
After an initial delay of 120 s, each parking sensor node generates a data packet with occupancy data every 60 s. The data are either 0 or 1, depending on whether the respective slot is vacant or occupied. The data packet is addressed to the data server whose address is sought through service discovery. In case of multiple data collators, the address of the first discovered server is considered, since it would be the most nearest server. The data collators exchange data once every 60 s between them and also send the collated data to on-site consumers.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Network Parameter** & **Value** \\ \hline Node placement & \(10\times 10\) uniform grid \\ Radio medium & UDGM \\ Distance between nodes & 30 m \\ TX Range/INT Range & 50 m/100 m \\ IoT devices having parking sensors & 96 \\ IoT devices as on-site data consumers & 2, top first node and bottom last node \\ Number of BR & 1 \\ BR position & Top or Center as per the models \\ Number of data collators & 1 or 4 depending on the model \\ Data collators position & Top/Center of quadrants/Center \\ Mode of operation & Storing mode \\ Run Time & 3600 s \\ Occupancy sensing interval & 60 s \\ Radio duty cycling for parking sensors & ContikiMAC \\ RDC for data collators and BR & None \\ Channel check rate & 8 HZ \\ \hline \hline \end{tabular}
\end{table}
Table 1: Configuration parameters for the simulation study.