Research On Message Relay Mechanism Of Spray And Wait Protocol In Social Delay Tolerant Networks

Social Delay Tolerant Networks (SDTNs) are delay tolerant networks that have sociality. Such networks are often faced with connection disruption because of node mobility, so end-to-end path does not exist at the same time. High delay, low delivery probability, long queuing time and long frequent network partition exists in these networks. How to improve the message delivery probability and reduce the message delay is an important content of message relay mechanism in social delay tolerant networks. In SDTNs, heterogeneous exists because of different contact rates between nodes due to different move speed and transmission capability, and selfish exists because nodes are unwilling to relay messages for other nodes due to limited resources. Responding improvement of message relay algorithm is proposed in this thesis in view of the above characteristics and the insufficient of existing algorithms.Architecture and key technology of SDTNs are firstly researched in this thesis to provide the foundation and general guidance to the research of the message relay mechanism in social delay tolerant networks. Based on this, the key research is on the problem of heterogeneous and selfish in SDTNs.In the study of heterogeneous in SDTNs, in order to solve the insufficient of current spray and wait protocol, the conception of node activity is defined in this thesis to weigh the importance of nodes in aspect of message dissemination in the whole network. Then, new spray and wait protocol with node activity is proposed to improve the performance in heterogeneous delay tolerant networks. Mathematical model, which can be used under varieties of the spraying protocols, is also proposed to analyze the expected delay of the protocol. Both theoretical and simulation results show that the spray token proportion with node activity is optimal, and the new protocol has better performance than other related protocols. Therefore, this protocol has high efficiency and good scalability.In the study of selfish in SDTNs, in order to solve the insufficient of barter trade which is very strict and causes poor network performance, the incentive mechanism with utilities and cooperation levels is proposed. Through prediction of selfish, the incentive mechanism can promote the message relay between cooperation nodes and the punishment towards selfish nodes. The incentive mechanism realizes on the routing protocol in this thesis, simulation results show that the incentive mechanism in this thesis improves the delivery probability and reduces the message delay. Message relay between cooperation nodes is promoted and selfish nodes are punished in this mechanism.The research can apply to the real application in SDTNs and provide idea in research on routing protocols in SDTNs, so it has good theory value and application prospect.