# A Method for the Rapid Propagation of Emergency Event Notifications in a Long Vehicle Convoy
## 3 Simulation Environment and the Convoy VANET System
### OLSR and AODV  
To form a point of comparison for the effectiveness of the Convoy VANET System, we initially chose to test against two popular ad hoc routing protocols: Optimized Link State Routing (OLSR) [20] and Ad hoc On-demand Distance Vector (AODV) [21]. These two protocols represent the typical forms of proactive and reactive approaches to ad hoc routing, respectively. The intention was to compare these two protocols against Convoy VANET in aspects such as message delay and route maintenance overhead. The experiment setup is similar to the experiments conducted on the Convoy VANET system; most importantly, the vehicles were spaced 30 m apart to induce an approximate 85% reception reliability. The only differences are that the convoy was only ten vehicles long (instead of 20) and the head of the convoy was unicasting its message to the last vehicle in the convoy (as opposed to broadcasting). The lack of broadcast is because OLSR and AODV do not handle broadcasts particularly well in ns3, and at this stage of the work, the experiment was meant to be a first pass at obtaining a point of comparison. The results of this experiment lend credence to the statements of [PERSON] and [PERSON] in that normal routing protocols are ill suited for VANETs [16]. In short, both OLSR and AODV failed to reliably propagate packets down a ten-vehicle convoy. The packet delivery ratio to the last vehicle was consistently well under 50%, with ratios as low as 10% being not uncommon. When it did manage to deliver a packet, it would occasionally be delayed by as much as one full second, which is obviously unacceptable. The exact results of these tests are not shown primarily because of the lack of  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Distance** & **Approximate Reception Reliability** \\ \hline
10 m & 95\% \\
30 m & 85\% \\
60 m & 65\% \\
90 m & 30\% \\
120 & 15\% \\
150 & 5\% \\ More than 200 m 1  & 0\% \\ \hline \hline \end{tabular}
\end{table}
Table 1: Approximate reception reliability vs. distance for the default wireless channel parameters.  
nuance and useful information. Also, this particular experiment is simple enough to build for oneself using the simulation parameters provided throughout Section 3.  
The reason why OLSR and AODV ultimately failed is due to the fact that they do not have any substantial reception reliability mechanisms. This is understandable given that they exist at the network layer of the typical OSI or TCP/IP stack instead of the transport layer. If we had added reliability guarantees using TCP instead of UDP, then we would have also foregone the ability to broadcast the messages at the transport layer (unless we make significant modifications to TCP). One could argue that transmission eavesdropping could still occur with TCP and that the participatory devices could still exchange data fragments until all have received the message. However, this approach only moves the problem up to the application layer, and the process for the efficient exchange of the eavesdropped data would still need to be defined.