# Self-Organizing and Scalable Routing Protocol (SOSRP) for Underwater Acoustic Sensor Networks
## 5 Simulation Results  
### Random Topology  
The behavior of the SOSRP was tested with different network sizes (from 50 to 100 nodes). For each network size, new random locations for the nodes were set, and consequently the ad-hoc topology would be different when the number of nodes changed. This was done to observe the effect of newly formed paths. Moreover, the transmission range was also swept (from 70 m to 100 m) to evaluate the effects on the connectivity in the network in terms of three parameters: end  
Another evident result is observed when only the transmission range is increased: the delay decreases. The reason is that the coverage area of the nodes is increased which, in turn decreases the hop count between the source and destination. This effect can be seen in Figure 6, where the delay for the longest path is as high as 1.6 s for a 50-node network and the shortest transmission range (70 meters). Another effect can be witnessed in Figure 8, where in a 70-node network with 700 meters of transmission range, the delay increases with respect to larger networks. This is due to large network area and random placement of node and increasing the number of hops, indicating that SOSRP is adopting the new paths efficiently leading to the sink node. However, a higher transmission range also increases the number of interferences because of spatial overlapping. The MAC implemented must works accordingly to the new situation, avoiding the new possible interferences. Figure 8: End-to-end delay for longest path in network of \(2000\times 2000\times 500\) m.  
Figure 6: End-to-end delay for longest path in network of \(200\times 200\times 200\) m.  
Figure 7: Average delay in network of \(2000\times 2000\times 500\) m.  
Another parameter to measure the efficiency in multi-hop routing protocols is the hop count in a route (path always ending in the sink node). A low number of hops in every route is desirable to keep a limited end-to-end delay. The results of the simulations are shown in Figure 9. In this set of Figures, there is a double interest: to know the number of hops of the routes generated by SOSRP, and to see the influence of the transmission range in this value. Generally, increasing the transmission range leads to the shortest routes (decreasing the hops count). This effect is evident in Figure 9b. On the other hand, it must be noted that when the network size changes, new random locations are selected for the nodes, changing the topology. For that reason, the result obtained for one network size is not the same case by adding a few nodes. Despite this, the results are consistent with a stable behavior of the SOSRP protocol proposed here. In order to evaluate the results in terms of energy, we must consider two logical effects. One of them is that as the network size grows, the energy consumption must also increase. The reason is obvious: more nodes are participating in sensing and transmitting data. The second logical effect is related to the transmission range: if it increases, the paths to the sink have fewer hops due to the nodes being not too far from each other. This fact leads us to reduce the energy employed in a small network area such as \(200\times 200\times 200\) m.  
Both effects can be seen in the results presented in Figures 10 and 11 for a network area of \(200\times 200\times 200\) m. Figures 10 and 12 calculate the total energy consumption for 50 rounds, while Figures 11 and 13 show the energy consumption only for the longest path. The energy consumed for transmitting data through the longest path (Figure 11) has a maximum of 2.5 mJ approximately for a network size of 50 nodes and a transmission range of 70 meters. The effect of choosing a large network area can be witnessed in Figures 12 and 13, where network area is \(2000\times 2000\times 500\) m. It can be observed  
Figure 9: Number of paths for different network sizes (nodes): (**a**) 50, (**b**) 70 and (**c**) 100.  
in Figure 12 how the energy tends to decrease when the transmission range changes from 500 to 600 meters.