## 4 Experiment and analysis
### Simulation Result Analysis
#### 4.2.2 Comparison Result Analysis between Algorithms under Different Number of Nodes
When the number of neighbor nodes increases, the message carrier can find more reliable relay nodes to perform efficient data transmission, thereby increasing the delivery ratio. The \"Spray and Wait\" algorithm performs a certain number of copies of the message in the network. When the number of neighbor nodes increases, the probability of encounter between neighbor nodes and destination node will increase, so the delivery ratio gradually rises from 0.45 to 0.84. The ICMT and EIMST algorithms achieve effective data transmission through cooperation between multiple nodes, but this is not an effective data transmission scheme when the cache space of nodes is limited. Therefore, compared with traditional algorithms, these two algorithms have some improvement in delivery ratio. When the number of nodes is 700, the transmission rate of ICMT algorithm even reaches 0.9. However, in general, the delivery ratio of MSSN algorithm is the highest among these algorithms. In Figure 9, we show the performance of the average end-to-end delay for each algorithm under different number of neighbor nodes. As we can see, in addition to the Epidemic algorithm and the Spray and Wait algorithm, the average end-to-end delay of other algorithms shows a gentle downward trend as the number of nodes increases. The reason why the average end-to-end delay of Spray and Wait has been rising is because the algorithm uses the mechanism that randomly transmits the replication of the message to the network to implement data transmission. When the number of nodes increases, the probability of the randomly distributed message reaching the destination node is reduced, so the average end-to-end delay rises from 68 to 123. As for the Epidemic algorithm, since the algorithm adopts the flooding data transmission mechanism, when the number of neighbor nodes exceeds 400, the replication of messages in the network increases sharply, thereby causing network congestion, and thus, the average end-to-end delay increases. Figure 8: Deliver ratio with different number of nodes. We can see that the average end-to-end delay of MSSN algorithm always stays at the lowest state from 63 to 20 when the number of nodes increases from 100 to 700. That is because when the number of neighbor nodes increases, the number of reliable relay nodes that the MSSN algorithm can find based on the mobile similarity and social similarity between nodes increases, and the average end-to-end delay decreases. The ICMT algorithm utilizes the cooperation mechanism between nodes to realize the effective transmission of data, and the EIMST algorithm carries out message forwarding through effective information management and community division. Therefore, compared with other two traditional algorithms, these two algorithms have higher average end-to-end delay. To sum up, compared with other algorithms, the MSSN algorithm is the best method to reduce the average end-to-end delay of network message transmission. The performance of each algorithm in terms of overhead on average with different number of nodes is shown in Figure 10. As the number of neighbor nodes increases from 100 to 700, the overhead on average of all the other four algorithms except the Epidemic algorithm is in a slowly decreasing state. Moreover, the overhead on average of the MSSN algorithm has been kept below 200. When the number of nodes is 700, the average overhead from the MSSN algorithm is even reduced by 68% as compared with those from spray and wait, and it is very close to those from the EIMST algorithm. The reason why the MSSN algorithm can always maintain a low overhead on average is mainly because the algorithm comprehensively utilizes the mobile node similarity and social attributes of the neighbor nodes to select reliable relay nodes, which is similar with the EIMST algorithm. When the number of neighbor nodes becomes larger, the relay nodes determined by the MSNN algorithm are more accurate and more numerous so that messages can be forwarded faster.