## 3 System Model Design
### Community Structure Contraction Strategy
In SCR, each node only forwards a copy of the message to a node that has the target node as a member of the cluster, but the clustering process needs time. Therefore, although the routing overhead is decreased, the routing overhead is still greater than that of the ESR algorithm. The routing overhead of ESR and EIMST remains at 25-65 because nodes spray a lot of

Figure 5: The packet delivery ratio of the ESR algorithm, EIMST algorithm, Spray and wait algorithm and the SCR algorithm at different node cache sizes and numbers of nodes. (**a**) The effect of node cache on packet delivery ratio; (**b**) The effect of node numbers on packet delivery ratio. Figure 6: The average end-to-end transmission delay of ESR algorithms, EIMST algorithm, Spray and wait algorithm and SCR algorithm when at different node cache sizes and number of nodes. (**a**) The effect of node cache on transmission delay; (**b**) The effect of node numbers on transmission delay. redundant data. As the cache and the number of nodes increases, this state will not change. In the ESR algorithm, all communities can help to share the routing pressure, which is less expensive than the above three algorithms. ## 5 Conclusions

In this paper, we learned some characteristics of opportunistic social networks and proposed an effective data transmission algorithm based on social relationships. In this algorithm, we use the social relationships of nodes to divide nodes into several communities based on the connection attributes between nodes, then judge the importance of nodes according to the influence of nodes on the network and delete some inefficient nodes. Then, the node's criticality is used to further reduce the community structure after reducing inefficient nodes. After the network is divided into several tight communities, we use the characteristics of the various communities in the network to allocate the number of data copies and transmit them through the community. This algorithm divides the nodes in the network by means of social relations and can effectively reduce the inefficient nodes in the network. Through close community information transmission, the efficiency of information transmission is ensured and the goal of low delay is realized. At the same time, to avoid congestion caused by popular nodes, the inefficient nodes are evaluated through the influence of nodes on information flow and the interaction between nodes, which reduces the network overhead. The routing and transmission of opportunistic social networks will still be the focus of this field in present and future research. In our future work, we will improve our data-forwarding algorithm based on more social network behaviors and further study security and privacy in social routing. Conceptualization, Y.Y. and J.W. ; Methodology, Y.Y. ; Software, J.W. ; Validation, Y.Y. ; Formal Analysis, Y.Y. and J.W. ; Investigation, Y.Y. and L.W. ; Resources, Z.C. and J.W. ; Data Curation, Z.C. and J.W. ; Writing--Original Draft Preparation, Y.Y. ; Writing--Review & Editing, J.W. and L.W. ; Visualization, J.W. ; Supervision, Z.C. ; Project Administration, J.W. ; Funding Acquisition, Z.C. This work was supported in part by the Major Program of National Natural Science Foundation of China [NO. 71633006]; The National Natural Science Foundation of China [NO. 616725407]; China Postdoctoral Science Foundation funded project [2017M612586]; The Postdoctoral Science Foundation of Central South University [185684]. Also, this work was supported partially by \"Mobile Health\" Ministry of Education--China Mobile Joint Laboratory. The authors declare no conflict of interest. Figure 7: The average routing overhead of the ESR algorithm, EIMST algorithm, Spray and wait algorithm and SCR algorithm when at different node cache sizes and number of nodes. (**a**) The effect of node cache on routing overhead; (**b**) The effect of node cache on routing overhead. ## References

* [PERSON] and [PERSON] (2016) [PERSON]; [PERSON] Sensor communication area and node extend routing algorithm in opportunistic networks.