# CoAR: Congestion-Aware Routing Protocol for Low Power and Lossy Networks for IoT Applications
## 5 Performance Evaluation
### Comparative Analysis  
**Packet receiving rate (PRR). ** It is defined as the ratio between the number of packets received by the root and the number of packets sent by the source nodes. Due to the high data traffic from several sensing nodes, the packets may converge on a particular intermediate node and that results in the packet drop because of the buffer limit being exceeded. This situation leads to a fewer number of packets being received at the destination and, hence the PRR decreases. However, PRR is measured in the different time intervals based on the average over periods of 20 s. Figure 5a shows the PRR of CoAR, ECRM, and RPL with respect to the varying time. The result depicts the trend of the metric in the protocols is fluctuating over the time. Yet, CoAR obtains the smaller PRR fluctuation than ECRM and RPL when congestion occurs. In contrast, RPL lost most of the packets compared to CoAR and ECRM. This was expected because RPL does not aware of congestion in the network. The reason behind the higher PRR in CoAR is that it detects the congestion proactively and can bypass the affected nodes by selecting less or non-congested parent node. We further analyze the PRR with respect to the varying traffic rate. For this, different traffic load is offered that is ranged from 60-540 packets per minute. The Figure 5b shows that the trend of the PRR at root node decreases with the traffic load increases. CoAR achieves a higher PRR compared to ECRM and RPL under high traffic load. Besides, CoAR maintains the maximum and minimum PRR of 100% and 72.7%, whereas, ECRM maintains 100% and 49.2% respectively. On the other hand, RPL decreases the PRR dramatically as the traffic load increases and reached a minimum of 27.5%. CoAR outperforms the ECRM and RPL by an average of 8.9% and 20.7%, respectively. Meanwhile, it is also more reliable against the gradual growth of the traffic load. Thus, it is shown that, at high traffic load, CoAR achieves higher PRR by exploiting the network resources in an effective manner. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Interference range & 70 m \\ Adaptation & 6 LoWPAN \\ Radio model & Unit Disk Graph Medium (UDGM) \\ Loss model & Distance loss \\ \multicolumn{2}{c}{Note type} & Tmote sky \\ Queue size & 12 packets \\ Queue type & FIFO \\ \(I_{min}/I_{doubling}\) & 0.75 s/8 s \\ Data link & CSMA; ContikiMAC (RDC) \\ Channel check rate & 16 Hz \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 4: Example topology of the network. **End-to-end delay. ** This metric is defined as the average time interval between packets generated at a sensing node until it successfully received at the root node. We use the warning line in queue monitoring to ensure the packets have a low delay. Figure 6 shows the evaluation of an average delay. The result shows, CoAR ensures the lowest packet delivery delay compared to the protocols. The delay of the RPL is significantly higher than CoAR and ECRM. This was expected because the RPL is unable to make a timely delivery of the data packets and needs to wait a long time in the buffer during congestion. In contrast to this, the CoAR can detect the occurrence of congestion and performs better. Because after detecting congestion, traffic is always routed through the non-congested or least congested parent in CoAR, so that packets are not queued in nodes buffering for a long time. **Packet loss ratio. ** Packet loss ratio is the ratio of the total number of data packets lost due to the buffer overflow to the total number of packets sent. Figure 7 compares the packet loss ratio with respect to the increasing traffic load of the protocols. The result shows the packet loss ratio increases with increases the traffic load. However, CoAR loses fewer packets at the buffer than others. When the data rate is high (i.e., 480 packets per minute), the packet loss ratio of the CoAR, ECRM, and RPL are about 20%, 27.6% and 50%, respectively.