# Geo-DMP: A DTN-Based Mobile Prototype for Geospatial Data Retrieval
## 4 Experimental Validation and Evaluation
### No Intermediate Cached Contents  
In this experiment, there are no cached contents on Nodes 2 and 3. All contents have to be retrieved from Node 4. The time sequence of transmission events is shown in Figure 16. The descriptions of the process are as follows:  
* Before 30 s: Initially, Node 1 generates a series of query bundles whose source regions are those where it resides, namely \(R_{1}\), \(R_{2}\), and \(R_{3}\), and target regions are those where Node 4 resides, namely \(T_{1}\), \(T_{2}\), and \(T_{3}\).
* About 200 s: Shortly after that, when Node 2 passes by Node 1, according to the routing strategy, because Node 2 comes from \(T_{1}\) while Node 1 falls outside all target regions, these queries are transferred to Node 2.
* About 400 s: Then Node 2 moves to point C and meets Node 3 there. As Node 3 has been to \(T_{3}\) which is the target region on a deeper level than \(T_{1}\), the only target region visited by Node 2, so Node 3 succeeds Node 2 to become the carrier of the queries.
* About 600 s: Node 3 continues to carry the queries until it reaches \(T_{3}\) and delivers them to Node 4. When corresponding response bundles are generated at Node 4, since neither of Node 3 and Node 4 has visited any of their target regions, i.e., \(R_{1}\), \(R_{2}\), and \(R_{3}\), they compare the minimum distance between their history regions and \(R_{3}\). As can be observed from Figure 15, for Node 3 this value is the distance between \(M_{3}\) and \(R_{3}\). It is shorter than that of Node 4, which is the distance between \(T_{1}\) and \(R_{3}\). As a result, Node 3 obtains all contents from Node 4 and turns around to point C.
* About 800 s: When Node 3 gets in touch with Node 2 again at point C, because Node 2 has moved across \(R_{3}\) while Node 3 has no chances to any of the target regions of response bundles, the contents are forwarded to Node 2.
* About 1000 s: Finally, on Node 2's path returning to B, the responses are successfully delivered to Node 1.  
This experiment proves that the system works properly on regular opportunistic multi-hop content retrieval from the data source. In the following two situations, the reasons why forwardings can happen under instructions of the routing scheme will not be explained repeatedly because they share the same mobility pattern.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**TimeNode** & **Node 1** & **Node 2** & **Node 3** & **Node 4** \\ \hline
0–30 s & Stationary at A & Stationary at C & Stationary at C & Stationary at E \\ \hline
30–230 s & Stationary at A & Moving from C & Moving from C & \\  & towards B & towards D & Stationary at E \\ \hline
230–430 s & Stationary at A & Moving from B & Moving from D & \\  & towards C & towards C & Stationary at E \\ \hline
430–630 s & Stationary at A & Moving from C & Moving from C & \\  & towards B & towards D & Stationary at E \\ \hline
630–830 s & Stationary at A & Moving from B & Moving from D & \\  & towards C & towards C & Stationary at E \\ \hline
830–1030 s & Stationary at A & Moving from C & Moving from C & \\  & towards B & towards D & Stationary at E \\ \hline \end{tabular}
\end{table}
Table 2: The movement pattern for experiments in Section 4.2.1.  
2 Full Intermediate Cached Contents  
In this experiment, we aim to ascertain if caches at a nearby place could be utilized. All contents requested by Node 1 are cached at Node 3 in advance. According to the temporal results in Figure 17, after the first round of movement of Node 2 between point B and C (about 400 s), all queries can be satisfied at Node 3. Consequently, responses are delivered to the requester in less time and fewer hops (about 600 s), which coincides with our expectation.