# Enhanced Message Replication Technique for DTN Routing Protocols
## 4 Simulation Studies
### Simulation Results  
The performance of the EMRT was analyzed by varying the node density (i.e., number of nodes). The results of the impact of the EMRT on Spray and Wait, EBR, and the DBRP at various node densities are shown in Figures 2-4. To clarify, \"Spray & Wait-EMRT\", \"EBR-EMRT\", and \"DBRP-EMRT\" refer to the application of the proposed EMRT on the original Spray and Wait, EBR, and DBRP quota-based routing protocols, respectively. The performance of Spray and Wait-EMRT, EBR-EMRT, and DBRP-EMRT is improved by the EMRT when the number of nodes exceeds 50. This is because the source node adaptively adjusts the initial maximum number of message replicas according to its own buffer size, allowing it to generate the appropriate number of copies for each message rather than relying on a fixed, limited number of copies for all generated messages. Figure 2 shows the relationship between the node density and message delivery ratio for different quota-based protocols. The delivery ratio for all protocols (i.e., the original Spray and Wait, EBR, and DBRP, as well as the enhanced Spray and Wait-EMRT, EBR-EMRT, and DBRP-EMRT versions) increases significantly as the number of nodes increases. This is because when there are more nodes, more of them are involved in delivering  
Figure 4: The latency average with different node densities. Figure 3: The overhead ratio with different node densities. Figure 2: The delivery ratio with different node densities. messages, and the number of replicas also increases, increasing the chance of the messages being delivered. In addition, Figure 2 shows a significant improvement when the proposed EMRT technique is applied to Spray and Wait, with results showing an improvement of up to 13% compared to the original Spray and Wait. This is because Spray and Wait relies on a fixed number of replicas for all messages, while Spray and Wait-EMRT uses a dynamic number of replicas based on the node's ability to carry the messages without causing congestion or wasting network resources. As a result, the EMRT reduces the number of copies of newly generated messages when the source's neighbors experience message congestion. The EBR-EMRT protocol also shows improvement when the EMRT is applied, with the delivery ratio increasing by up to 8% compared to the original EBR. This is because, in addition to directing replicas towards high-density areas, EBR-EMRT controls the number of replicas based on the capability of the node, taking advantage of the available size of the node buffer to carry and store more copies of the message until a good forwarding opportunity arises. Finally, the DBRP-EMRT also achieves an improvement of up to 10% compared to the original DBRP by controlling the level of congestion in the network to improve the delivery ratio, by ensuring that the number of replicas is appropriate for the available network resources. Figure 3 shows the relationship between the overhead ratio and node density. As the node density increases, the overhead ratio decreases for all protocols, because these quota-based protocols rely on a small number of message copies, so they are not greatly affected by the increasing number of nodes. At the same time, the figure also shows the results of applying the EMRT to Spray and Wait, EBR, and the DBRP in terms of the overhead ratio. There is no significant reduction in the overhead ratio of DBRP-EMRT, while the overhead ratios of the Spray and Wait-EMRT and EBR-EMRT protocols are reduced by up to 9%, and 6%, respectively, compared to Spray and Wait and EBR. This is because the network resources are controlled and congestion is reduced by relaying messages based on the rate of encounter and the level of network congestion (i.e., available network resources), resulting in a low overhead ratio. This means that when a node has sufficient resources, such as free buffer space and energy, the number of replicas for newly generated messages will be increased. Otherwise, the number of copies of newly generated messages will be decreased.