## 4 Performance Evaluations
### Simulation Results  
Figures 3 and 4 show the performance comparison for 50 randomly selected sources. We have used the same set of sources for each mechanism. We have gradually increased the source data rates to measure the impact of increasing traffic load on the performance metrics. Figure 3(a) shows the network throughput with increasing data rates. When the source data rates are small (_i.e._, up to 6 packets/s, all of the mechanisms perform almost equally, because the network remains lightly loaded. However, as the offered load is increased, the channel capacities are exceeded and the performances of the respective protocols start to vary. Due to the static channel allocation, the throughput of TMCP depends on the locations of the sources. The channel with the highest number of nodes is overloaded, while many other channels remain underloaded. The dynamic channel allocation of DM-MAC achieves a higher throughput than TMCP until all of the channels in TMCP are overloaded. LPMC achieves the maximum throughput because it does not require channel switching and it allocates channels dynamically. Furthermore, the fair throughput of the sources (_i.e._, each source achieves the reliability) in LPMC is achieved up to a source rate of 11 packets/sec where the network throughput is 274 kbps. DM-MAC and TMCP achieve fair throughput up to source rates of 9 packets/s (where the network throughput is 216 kbps) and 7 packets/sec (where the network throughput is 174 kbps), respectively. Figure 3 shows the delivery ratio at the sink, and as expected, LPMC outperforms the other two mechanisms at higher traffic loads. In LPMC, whenever a channel used by a single TB is overloaded, it updates the paths (_i.e._, it partitions the overloaded TB into two groups and creates a new TB that connects one group to the sink) and assigns a lightly loaded or unused channel to the new TB. Therefore, the number of packet losses due to congestion and contention decreases, and LPMC achieves a higher delivery ratio than TMCP and DM-MAC, while increasing the offered load. At higher traffic loads, DM-MAC experiences more intra-flow interference and therefore, DM-MAC's delivery ratio becomes less than TMCP's delivery ratio. Figure 4 shows the average end-to-end delays experienced by the successfully delivered packets. When the traffic load is low, all of the mechanisms experience small delays because the channels are operated with tolerable loads. Moreover, with a small amount of traffic, the channels do not become overloaded, which results in minimal channel switching (if any). However, as the traffic load is increased, LPMC outperforms both DM-MAC and TMCP in terms of the average end-to-end delay. This is because  
Figure 4: Performance comparison for randomly selected 50 sources with different data rates: (a) average end-to-end delay, (b) average channel capacity when all nodes achieve a fair throughput. Figure 3: Performance comparison for randomly selected 50 sources with different data rates: (a) network throughput, (b) delivery ratio. in LPMC, the nodes in a single path do not need to switch their channels to receive or forward a packet. TMCP has less delay than DM-MAC because of the static channel allocation. With DM-MAC, the delay is the highest, because the nodes in a single path need to switch channels more frequently. Figure 4(b) shows the channel utilization when the maximum fair throughput is achieved. TMCP achieves the minimum channel utilization, whereas it is at a maximum for LPMC. In case of TMCP, because of the static channel allocation, the channel utilization depends on the network topology. Therefore, the achieved throughput of different channels differs significantly. In contrast, DM-MAC and LPMC aim to use the smallest number of channels needed to satisfy the traffic load. As long as an acceptable delivery ratio is satisfied, LPMC does not add a new channel and achieves maximum channel utilization. Because of the added switching delay, DM-MAC cannot utilize the channel as fully as LPMC.