# A Distance-Vector-Based Multi-Path Routing Scheme for Static-Node-Assisted Vehicular Networks
## 5 Evaluation
### Results  
Figure 11 shows the results on basic communication performance. Figures 11a-c show the performance comparison results under the flush rate 0%. In Figure 11a, we see that delivery ratio is all good and comparable. Note that both RDV and MP-RDV exceed the predefined expected delivery ratio \(P=99\%\). In Figure 11b, we see the trend that delivery delay naturally reduces as vehicle density increases. Note that MP-RDV significantly improves delay compared to RDV, and the value is close to SADV. In Figure 11c, we see that the number of SADV's packet copies is far larger than the others. Note that the difference between RDV and MP-RDV comes from the rounding error of the ceiling function shown in Formula (3). Those results clearly show the characteristics of the three schemes; all achieve a high delivery ratio while SADV requires a large amount of duplication load, RDV expenses delivery delay, and MP-RDV performs the best without degradation in neither of them.  
As for the effect of flush events, i.e., the effect of uncertainty of vehicle behavior--see Figure 11d-i. The case of flush rate 1% is shown by Figure 11d-f. Although the trend is not so different from the case of 0%, we find that the delivery ratio of SADV is significantly degraded. This means that SADV is so sensitive to flush rate, whereas Adaptive Packet Duplication (APD) deployed in RDV and MP-RDV well works to keep the delivery ratio to 99%. The cases when the flush rate is as high as 2.5% are shown in Figure 11g-i. The same trend as 1% case is still kept, and RDV and MP-RDV still keep 99% delivery ratio. In Figure 11h, we see that the delay of RDV and MP-RDV is increased, meaning that RDV and MP-RDV is sensitive to flush rate on delay performance. In Figure 11i, the number of packet copies for  
Figure 11: Performance with various vehicle density: delivery ratio, delivery delay, and the number of duplicated copies are measured for each flush rate \(0\%,1\%\), and 2.5%.  
RDV and MP-RDV increases, which is natural because they require larger number of packet copies when the packet loss ratio goes high. In contrast, SADV's delivery ratio in Figure 11 is significantly degraded and the load due to packet copies in Figure 11 is reduced as well. This is because many packets are lost early before generating many packet copies, meaning that SADV is very weak against flush events. To summarize the effect of flush rate, we see that RDV and MP-RDV are able to keep the given delivery ratio 99% although delay and duplication load increases to some extent, whereas the performance of SADV significantly degrades due to packet loss.  
Performance under variation of traffic load is shown in Figure 12. With flush rate 0%, we see that RDV fails to keep 99% delivery ratio when generating over 30,000 packets, whereas MP-RDV keeps 99% even at 50,000 packets. From this, we clearly conclude that MP-RDV has a larger traffic capacity due to the load balancing function over the multiple paths. In a 1% case, the same trend is seen although MP-RDV fails to keep 99% delivery at the point of 30,000 packets generation. In a 2.5% case, all fail to keep a high delivery ratio, while MP-RDV marks the best performance among them. In summary, the results show that MP-RDV has the largest network capacity among three, and has the highest ability to keep the expected delivery ratio.  
Finally, in Figure 13, we show the results on robustness against failure. We see that the performance of MP-RDV and SADV is better than RDV regardless of flush ratio, which is because multi-paths improve the robustness against failure. This means that the robustness of RDV against failure is improved with multi-path functionality.