## 5 Results  
As discussed previously, it is important that no packets are leaked to hostile aircraft. If traditional omnidirectional antennas are used, there is a very high risk that a packet is leaked. This risk is reduced if directional antennas are used. However, even when using directional antennas, there is still a risk that a packet is leaked if there are adversary aircraft close to the sender or the receiver (see Figure 4). The main benefit of the HDARP protocol is that it considers forbidden sectors so that the risk for leaked packets is substantially reduced. Tables 2 and 3 show the reduction of leaked packets when using directional antennas instead of omnidirectional antennas for the five protocols, which the HDARP protocol is compared to for scenarios 1 (R4B4) and 2 (BVR). The table shows that using directional antennas reduced the number of leaked packets with a factor 133 to 222 (depending on the protocol) for Scenario 1 and with a factor of 110 to 7464 for Scenario 2. This means that the reduction of leaked messages due to using directional antennas is very high. However, some packets are still leaked to an adversary aircraft. Figure 6 shows the number of packets that are leaked when using directional antennas. The averages and the 99% confidence intervals are shown in the figure. The confidence intervals are very small with the exception of DSR-UU that has a somewhat larger confidence interval than the other protocols. DSR-UU is a complete protocol implementation for the Linux operating system that was later integrated with OMNEST, unlike the other protocols, which are pure simulation implementations. However, it is difficult to assess whether this is the reason for the large confidence intervals observed without an in-depth code review, which is outside the scope of this study. The figure shows that the HDARP protocol has (virtually) no leaked packets, whereas the other protocols have a substantial number of leaked packets for the scenarios considered here. \begin{table}
\begin{tabular}{l c c c c c} \hline  & **AODV** & **BATMAN** & **DSDV** & **DSR-UU** & **OLSR** \\ \hline Omnidirectional antennas & 199,562 & 211,454 & 149,051 & 137,781 & 147,410 \\ Directional antennas & 1256 & 1588 & 782 & 620 & 762 \\ \hline Reduction ratio & 159 & 133 & 191 & 222 & 194 \\ \hline \end{tabular}
\end{table} 
Table 2: Reduction of the number of leaked packets when going from omnidirectional antennas to directional antennas for each of the studied protocols for Scenario 1 (R4B4). \begin{table}
\begin{tabular}{l c c c c c} \hline  & **AODV** & **BATMAN** & **DSDV** & **DSR-UU** & **OLSR** \\ \hline Omnidirectional antennas & 3,138,553 & 2,524,658 & 1,393,752 & 1,311,349 & 1,194,179 \\ Directional antennas & 1186 & 955 & 272 & 11,953 & 160 \\ \hline Reduction ratio & 2646 & 2644 & 5143 & 110 & 7464 \\ \hline \end{tabular}
\end{table} 
Table 3: Reduction of the number of leaked packets when going from omnidirectional antennas to directional antennas for each of the studied protocols for Scenario 2 (BVR). In order not to leak packets, the HDARP protocol sometimes avoids sending packets directly from the sender to the destination, since such direct transmissions could be detected by adversary aircraft (see Figures 3 and 4). This means that one would expect that the number of hops and, as a consequence of this, the average end-to-end packet delivery time of HDARP could increase compared to protocols that do not consider forbidden sectors. Packet delivery time includes queuing time in each node on the path, as well as transmission and propagation delay for each link of the path. Figure 7 shows that average packet lifetime of the HDARP protocol is longer than the average packet lifetime for four of the other protocols. The difference is small for Scenario 1, but rather significant for Scenario 2. In practice, the type of traffic routed by HDARP will consist mostly of voice-over-IP communication. Conventional wisdom indicates that for this type of traffic, the one-way latency should not exceed 150 ms [43; 44].