# Development of a Social DTN for Message Communication between SNS Group Members
## 5 Evaluation
### Route Establishment Time  
We measured the time it takes between the time when the source node transmits an rreQ_m and the time when it receives an rreP_m. The route establishment request time is defined as a period between the time when the source node starts advertising operation and the time when the destination node has received the message and confirms that the communication with the relay node has been discarded, as shown in Figure 5. The route establishment response time is defined as a period between  
Figure 9: Text data transmission screen. (**a**) Text input screen; (**b**) Screen when discovery operation has been started; (**c**) Screen when advertising operation has been started. the time when the destination node completes the creation of an rreP_m based on the rreQ_m it has received and the time when the source node has received the rreP_m and starts advertising operation to send data, as shown in Figure 5. These two types of time were calculated from stored log data. Using the terminals shown in Table 6 and the network structure shown in Figure 8, we measured the route establishment time three times for each of the three patterns (three different numbers of hops). Detailed experimental conditions are shown in Table 9. Relay nodes were located between the source node and the destination node. When a relay node received a message from the source node, the person who held the relay node began to walk. The average values of the measurements are shown in Figure 10.  
In cases where the distance was 100 m, as the number of hops was increased from one to two, the average route establishment time increased moderately from 142 s to 185 s but when the number of hops was increased to four, the average route establishment time jumped to 437 s. In cases where the number of hops was two, the route establishment time for a distance of 100 m was much shorter than that for a distance of 250 m. However, in cases where the number of hops was four, the route establishment time for a distance of 250 m was 495 s, which was only slightly longer than the route establishment time for a distance of 100 m, which was 437 s. In spite of the fact that the difference in distance was 150 m, the difference in route establishment time was only 58 s. This difference was very small considering that it takes 108 s for a person to walk 150 m at a speed of 5 km/h. The route establishment time per distance for the case of 100 m was much longer than that for the case of 250 m. This indicates that, when there are many other terminals in an area within which a terminal can communicate with another terminal, the route establishment time increases. More specifically, according to the specifications of Nearby Connections API ([PERSON], 2007), a communication is established when the Advertiser broadcasts a message and the Discoverer receives that message. Figure 10: Required route establishment time. \begin{table}
\begin{tabular}{l c} \hline \hline
**Item** & **Value** \\ \hline Number of terminals & 3, 4 or 6 \\ Number of hops (i.e., number of relay nodes) & 1, 2 or 4 \\ Number of experiments & 3 experiments per pattern \\ Use of different community tokens & None \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Experimental conditions for the measurement of the route establishment time. If there are many Advertiser terminals, it takes a longer time for the Discoverer to receive messages. Specifically, even if a terminal sets up a connection with another terminal, it rejects reception of messages from this terminal if it finds that it does not have information about this terminal in its routing table. In other words, a terminal cannot decide whether to permit message exchange with another terminal until after it has set up a connection with that terminal. This means that, the more terminals there are in an area within which a terminal can communicate with other terminals, the more processing load it takes for the terminal to receive messages. This results in an increase in the time needed to establish a route.