# Building Realistic Mobility Models for Mobile Ad Hoc Networks
## 6 Real Shipping Movement Model
### Results and Discussion
#### 6.8.2 Packet Delivery Ratio on the Random Waypoint Shipping Model  
DSDV poses a significant issue when using this scenario with the random waypoint movement model. DSDV simulations fail to complete for all except for the 30-km radio range. This is due to a limitation within the DSDV code supplied with ns-2. In this code, the maximum number of entries in an update packet is approximately 100, and multiple packets per update are not possible. This means that in situations where connectivity is limited, DSDV implementation in ns-2 will fail as it tries to find routes when nodes move, resulting in the update packets overflowing. Therefore, the RWP model cannot be used in this scenario to evaluate DSDV. The realistic model does not have this issue, as the node movements are more constrained, resulting in fewer routing changes. Thus, smaller update packets are below the permitted thresholds for the implementation. Due to the DSDV implementation flaw, the discussion for this section focuses only on AODV and DSR.  
Two sets of runs are conducted for the random waypoint model using AODV and DSR. In the first set of runs, all the nodes are included in the random position and movement generation, and  
Figure 12: Realistic Shipping Model Packet Delivery Ratios (PDRs).  
the results are shown in Figure 13. The second set of runs has four sink nodes (mapped to the base stations in the realistic model), which are fixed to their real-world positions, and the remaining nodes are included in the random position and movement generation. The results for this version are shown in Figure 14.  
Figure 14: Moving Base Station Random Waypoint Model Packet Delivery Ratios.  
Figure 13: Moving Base Station Random Waypoint Model Packet Delivery Ratios.  
In either case, there is no concept of a shipping lane in the random model. This means that the nodes are more evenly distributed across the whole area. This is a large area for a MANET model, and node density is relatively low, resulting in much lower PDRs than for the realistic model. It also means that the PDRs decrease more steadily with reduced radio range than in the realistic model. There is no sudden failure as the radio range reaches a certain value.  
When the four sink nodes (number 0-3) are not fixed, but their positions and movement are random, just like all the other nodes, the results for the four base stations are not significantly different (see Figure 13). Any node in this model could be used as a sink, and effectively, there is no difference in movement between base station nodes (i.e., sinks) and any other node. For the highest radio ranges modelled, both protocols manage to establish usable PDRs at over 85%. As the radio range drops to 20 km, the PDR drops to 70% or below, which is approaching the practical limit for use. Although not as dramatic as in the realistic model, the drop in PDR between the 20-km and 15-km radio range is still marked and certainly would prevent a viable MANET from being established using a radio range of 15 km.  
Where there are fixed base stations acting as sinks for the data packets, the data delivery is somewhat less successful at higher radio ranges but significantly better at lower ranges (see results in Figure 14). In particular, at a 15-km radio range, the model with fixed base stations shows significantly better data delivery. Also, when the target nodes are fixed, there is a significant difference between the delivery ratios depending on which base station is being contacted. When the base stations are fixed, AODV gives a better result in the middle of the radio ranges, while DSR is better at both the 10-km and 30-km range. The PDR results from using the random waypoint mobility model would indicate that a radio range of at least 20 km is required to approach usable delivery reliability when using AODV, whereas 25 km would be required for DSR. Thus, if a RWP model is used, the radio range will be a deciding factor for choosing one of the protocols.