## 4 Performance Evaluations
### Simulation Results
Figure 5 shows the results when end-to-end reliability is considered. In this case, the required reliability becomes 1 and lost packets are recovered by the end-to-end retransmissions. As shown in the Figure 5(a), with end-to-end reliability, the nodes using LPMC achieve a fair throughput up to a source rate of 7 packets/sec (where the network throughput is 176 kbps). Whereas, it is only 126 kbps for DM-MAC and 112 kbps for TMCP. Thereafter, all the mechanisms experience variations in achieved throughput because of the increased overhead caused by acknowledgments and end-to-end retransmissions. However, LPMC outperforms others as its load estimation policy (_i.e._, the NLD module discussed in Section 3.3) can effectively estimate whether a channel is overloaded or not, even when end-to-end reliability is considered. DM-MAC's load estimation only considers the local loss, and with the increased load of the end-to-end retransmission, most of the intermediate nodes are forced to change their channels (based on local condition), and they need to switch their channels for data forwarding. This increases the overhead, and decreases the network throughput. On the other hand, TMCP does not consider the load for its static channel allocation, and the channels become overloaded with the increased load of the end-to-end retransmissions. While LPMC can use the unused channels due to its dynamic channel allocation, TMPC's static allocation does not allow the nodes to change their channels. Especially, when the nodes send their data at a high rate, or number of nodes from a smaller area send their data simultaneously, which might overload a particular channel and the nodes using that channel have a lower throughput. The dynamic channel allocation of LPMC can effectively divide the nodes into different channels and achieve a fair and efficient throughput, as long as the overall load is lower than the network capacity. Figure 5(b) shows the average end-to-end delays incurred by the compared mechanisms as we increase the traffic load. We measure the average end-to-end delays of the successfully delivered packets. It is noticeable that average end-to-end delays of all the mechanisms with end-to-end reliability are higher than that of end-to-end delays (without considering end-to-end reliability as Shown in 4(a)). We measure that on an average only 7 control overhead of the end-to-end retransmissions, overall network load increases which cause increased delay as compared to the absence of the end-to-end retransmissions. Initially, TMCP experiences higher end-to-end delays than that of DM-MAC and LPMC. Because of the static channel allocation of TMCP, the channels become overloaded fast and packets are lost due to increased congestion and contention, which increases the average end-to-end delays. On the other hand, when the traffic load becomes high, DM-MAC experiences more channel switching. This  
increased switching delay contributes to the increased end-to-end delay while using DM-MAC at higher traffic load. Figures 6 and 7 show the performance comparison for a varying number of sources from a randomly selected location. Each source generates data at a rate of 20 packets/s. We measure the impact of increasing the number of sources on various performance metrics. Due to the static channel allocation, some of the channels are kept idle in TMCP, achieving the minimum throughput with more than 10 sources, as shown in Figure 6(a). DM-MAC requires channel switching when multiple channels are active, and the network throughput is less than that of LPMC. Figure 6(b) shows the delivery ratio of the different mechanisms, and LPMC achieves the highest delivery ratio. In the case of TMCP, some channels are overloaded quickly, while others remain underutilized, because the sources are selected randomly. Therefore, packets tend to get lost, due to the increased congestion and contention, and the delivery ratio drops significantly as the number of nodes is increased.