## 6 Performance Evaluation
### Results by Epidemic, GSaR, TCCB, TC, and PRoPHETv2
#### 6.3.1 Case (a)  
Figure 9 depicts that all the policies can increase the successful delivery rate with a longer TTL period. Epidemic and TCCB unboundedly replicate messages to the encountered nodes, thereby inducing more message traffic. When the TTL \(>\) 8 h in Epidemic and GSaR and the TTL \(>\) 9 h in the TCCB, the delivery rate decreases, as shown in Figure 9a. However, in the MPMF, it continues to increase when the TTL \(>\) 8 h. In Figure 9b, when the TTL \(>\) 3 h, the MPMF has a lower overhead ratio compared with the other policies. In Figure 9c, Epidemic outperforms the other policies regarding average latency. However, as depicted in Figure 9d, it has a higher average hop count (hops) in comparison with the other polices. Relatively, TC attains the lowest delivery rate when compared with all the other policies. Both the MPMF and GSaR consider the location information and spray a limited number of copies of a message in the network, while PRoPHETv2 considers the DP estimates of directly encountered nodes with the destination and generates more messages than the MPMF and GSaR. Epidemic performs in a flooding-like message replication, and with a sufficient buffer and lower TTL, it can have a high delivery rate but induce more overhead. Likewise, the TCCB considers temporal closeness with the destination or higher centrality in the network to take a forwarding decision. It cannot avoid repeatedly replicating messages to other nodes in closer social relationships, resulting in a considerable overhead  
Figure 11: Performance comparison of MPMF in TVCM trace (\(W_{0}\) = 0.5, \(L\) = 20, \(\epsilon\) = 60, \(\alpha\) = 0.6, and buffer size = 10 MB). ratio. In TC, a message is forwarded when a message-carrying node and an encountered node belong to the same group/community, or if the encountered node has better data forwarding capabilities. With a longer TTL period, the MPMF will hold messages longer on nodes and induce a limited amount of message replicating and relaying operations. Thus, a buffer overflow can be mitigated so that messages can reach their destinations at higher chances. Although both GSaR and MPMF replicate a message with a limited number of copies to nodes moving closer to the destination, GSaR fails to achieve a sound performance. In GSaR, when a message-carrying node encounters a relay closer to a destination and can deliver a message earlier, it replicates the message to this relay and deletes that message from its buffer. The policy of deleting messages possibly degrades the performance of message delivery. With only one copy left for a message, GSaR will still replicate the message. Those buffer replacement operations possibly cause other messages to be removed and induce more overhead in the network. While TCCB uses temporal closeness and centrality to avoid blind replication, its overhead ratio becomes lower than Epidemic. Epidemic policy replicating a message multiple times increases the possibility that one of the message copies is successfully delivered within the shortest time. At the same time, creating more copies increases the average hop count. This observation is apparent from Figure 9c,d, where Epidemic has a lower latency when the TTL = \(5\to 9\) h and a higher value of hops for TTL = \(1\to 10\) h. For the MPMF, a limited number of copies are replicated for each message, which results in lower hop counts than Epidemic and PRoPHETv2. Conversely, messages with a longer TTL remain in the buffer for a longer time, resulting in higher latency. In TC, when a message-carrying node has not encountered other nodes with higher relaying capabilities in some time period, it removes the message from its buffer. By this way, fewer copies of the message are relayed in the network, resulting in lower delivery rate and overhead ratio. Figure 10 depicts the comparative results under the NCCU trace. As the results in Figure 10a indicate, Epidemic, TCCB, TC, and PRoPHETv2 perform better.