## 4 Simulation Works and Discussion
### Multiple Sinks with Single Radio  
In our previous work [7, 8], we examined the effect of the sink received data from sources within range that are sending data to be accepted. It was observed that the more sources sending to the single sink the more delays were encountered. In this scenario we have increased the number of sink nodes to receive data from sources within the ranges of the sink nodes. No modification to our MC-DCF protocol was made, except to increase the number of sinks to three with each having a single radio and doing channel switching as in our previous work. The simulation last for 500 seconds all nodes send CBR every 2 seconds.  
**Figure 3.** Delay impact from source nodes when using multiple sinks with single radio interface.  
Figure 3 show the delay impact with the increase in sink nodes that are receiving data packets from the sending nodes within its range. We have observed that with three channels there has been a 53% reduction in delay at the sink side when compared to the high level of delay in our previous work [7,8] using only one sink node. In the same Figure 3 with two channels sending data from sources, there has been an approximately 32% delay improvement. Single channel and 802.11 DCF show little improvements. This indicates that single channel performance does not improve with increasing sink nodes as the decisions are based on the window size resetting, backing off, wait states and the fact that all nodes are contending for the same medium. MC-DCF with multiple channel switching and single radio interfaces can yield a better performance, when using multiple sinks compare to single channel which shows a better performance in previous work.  
Figure 4 shows an improvement of over 41% for three channels with packet delivery ratio when the number of sink increases by three as compare to single sink node in our previous work. With two channels sending data from the sources to the sinks there has been improvement by over 25% comparing to the poor performance experienced with a single channel. Similarly, where the delay with a single channel shows no significant improvement, packet delivery ratio shows no major improvement.  
The aggregate throughput in Figure 5 of the overall system with source nodes sending to the sinks have shown that with three channels 38% more data have been delivered to the sink compared to that of a single channel. The single channel in all instances has not shown any significant improvement with increasing of sink nodes to receive data from the source nodes.  
Figure 4: Delivery ratio impact from sources when using multiple sinks with single radio interface.  
By analyzing the impact of MC-DCF with one to three channels in comparison with the original 802.11 DCF, we observed that increasing the number of sink nodes results in an improvement when two or three channels are used. There was little or no improvement using a single channel or the original 802.11 DCF which only operates on a single channel. The reason for this improvement is that each sink has less data to receive from the senders. The same amount of data simulated in previous work was going to a single sink node. The improvement proved that increasing the sink nodes gives a better performance as the traffic load has split to be received by more sink nodes. Therefore channel switching by a single radio has less data to retrieve, therefore less time is spent switching between channels from senders and the queuing of packet data has been reduced.