# Research on Secure Community Opportunity Network Based on Trust Model
## 4 Performance Evaluation
Although the SCTM algorithm employs restricted copy forwarding, it selects relay nodes with higher centrality, thus enhancing forwarding efficiency. Augmenting node cache size alleviates caching pressure on the backbone network and further improves forwarding success rates. Notably, when node cache size reaches 30 MB, the SCTM algorithm achieves a transmission success rate of approximately 90%, demonstrating its lower dependency on node cache size. Figure 6 depicts the relationship between average transmission delay and node cache. Notably, the Direct and Spray algorithms exhibit minimal dependency on node cache, with average transmission delay maintaining stability. Contrarily, while the Epdic and BubbleRap algorithms alleviate network congestion with increasing node cache, nodes storing more messages prolong the survival time of messages that should otherwise be discarded due to tardiness, resulting in a slight reduction in algorithmic average delay. The SCTM algorithm selects next-hop relay nodes based on considerations of node centrality and remaining cache. Although increasing node cache mitigates cache pressure on highly central nodes, these nodes typically maintain low residual cache levels after receiving  
Figure 5: Deliveryratio and node buffer. numerous messages. Consequently, the SCTM algorithm may opt for nodes with lower centrality but higher residual cache when selecting next-hop relay nodes, leading to a modest increase in average forwarding delay, albeit remaining at a low level. As illustrated in Figure 7, the increased node cache of the Epdic and BubbleRap algorithms results in fewer messages being discarded due to buffer overflow, leading to a reduction in the number of forwarding instances required for successful message transmission and a significant decrease in routing overhead. Conversely, the SCTM algorithm's strategy of selecting nodes with low centrality but ample remaining cache space as next-hop relay nodes leads to messages traversing more nodes and being forwarded more frequently, resulting in a slight increase in routing overhead. Meanwhile, the Direct and Spray algorithms exhibit minimal changes. Figure 6: Latency_avg and node buffer. Figure 7: Overhead and node buffer. Furthermore, this study investigates both node-sparse and node-dense networks in real-world scenarios. Comparative experiments were conducted by adjusting the number of nodes in the network during simulation. Figure 8 illustrates the relationship between the transmission success rate and the number of nodes for the Direct, Epdic, Spray, BubbleRap, and SCTM routing algorithms. With an increase in the number of nodes, the transmission success rate of the SCTM algorithm exhibits a gradual rise. This phenomenon arises from the heightened frequency of node interactions as the network expands. Consequently, the SCTM algorithm adeptly identifies superior forwarding nodes, leading to a sustained enhancement in transmission success rate throughout the network. Notably, when the network comprises 1000 nodes, the transmission success rate surpasses that of the Spray algorithm. Conversely, the Epdic and BubbleRap algorithms, utilizing flooding forwarding strategies, witness an escalation in redundant message copies within the network due to increased message forwarding, thereby diminishing the transmission success rate. As for the Direct and Spray algorithms, their average transmission delay hinges on the encounter probability between the message-carrying node and the destination node, with minimal influence from the network size. Moreover, the transmission success rate of these algorithms stabilizes over time, largely dictated by the encounter probability between the message-carrying node and the destination node. Figure 9 depicts the relationship between the average transmission delay and the number of nodes. As the network expands, node interactions become more frequent, thereby increasing opportunities for message forwarding.