# A Distance-Vector-Based Multi-Path Routing Scheme for Static-Node-Assisted Vehicular Networks
## 6 Conclusions  
We proposed two extensions on RDV to further improve the communication performance in static-node-assisted vehicular networks. From comparison with SADV, we extracted two points of potential improvement and designed them as an extension to RDV. The first extension is MP-RDV, a multi-path extension to RDV in which multiple paths are utilized for forwarding each of the packets to avoid load concentration on the shortest paths as well as to improve the delay performance. The second extension is the delay metric that measures the expected delivery delay as the sum of the waiting delay on nodes and the transportation delay between nodes. Our extensions inherit the characteristic of RDV to provide reliable communications that satisfies a pre-configured delivery ratio expectancy with a minimum packet duplication overhead. RDV achieves this in the following mechanisms. First, SVS measures statistics of vehicular movement at each static node located at major intersections to predict the outgoing direction of vehicles, and, second, APD controls the number of duplicated packets to achieve the required expected packet delivery ratio while minimizing the load of duplicated packets. The multi-path selection in MP-RDV cares for selecting two next-relays at each static node to distribute packets into the optimal paths while preventing routing loops. APD is also extended to handle multiple paths such that the load is well balanced among paths while guaranteeing preconfigured expected packet delivery ratio. The delay metric is also designed to work in the framework of RDV as well as MP-RDV. The waiting delay and the transportation delay are measured in cooperation with related nodes, and the measured metrics are advertised through the distance-vector messages in RDV.  
Evaluation results show that MP-RDV has better performance in total than the conventional schemes considering the balance of several important measurements. MP-RDV is proven to have well-maintained delivery ratio, lower delay, high network capacity with load-balancing effect, and better fault tolerance performance. This shows that the multi-path strategy is beneficial in RDV schemes. On the other hand, the delay metric has been proven to have reduced performance compared to the traffic-volume metric that was proposed as a built-in metric in RDV. We found that, although those two metrics chose almost the same set of forwarding paths under stable vehicular traffic patterns, the delay metric is statistically unstable under fluctuation on traffic patterns coming from traffic signals, unforeseen driver's behaviors, etc. Finally, we conclude that multi-path strategy with traffic-volume routing metric is the best choice for the RDV scheme.  
In considering future work, we would note that this work is a pure theoretic framework that does not use any practically available observable data such as several sensors on vehicles, current location, and current moving directions. Enhancing the proposed framework utilizing those sensor data is one of the most interesting directions for the future.  
[PERSON] and [PERSON] conceived and designed the proposed method MP-RDV. [PERSON] implemented the simulation software and conducted simulation work. [PERSON] directed the analysis and evaluation work.  
The authors declare no conflict of interest.