Research On The Node Cooperation Mechanism For Delay Tolerant Networks

Delay tolerant networks(DTNs)are the networks without a stable end-to-end connection,and have the characteristics of long delay,intermittent interruption,small node buffer and low computation capacity.DTNs have been widely used in the fields of social networks,vehicular networks,disaster relief,environmental monitoring,and military strategy.At present,relevant scholars have proposed some DTN routing and dissemination protocols to deliver data effectively.Nodes are assumed to be selfless and fully cooperative in these protocols.However,due to the limited buffer,energy and other resources,there are lots of selfish nodes in DTNs.The non-cooperation degree among nodes will increase with the number of selfish nodes,which will degrade the routing performance severely.Therefore,for the selfishness of DTN nodes,it is very important to design a cooperation mechanism which can effectively stimulate selfish nodes to cooperatively forward messages to improve routing performance.In order to stimulate DTN selfish nodes to cooperatively forward messages and improve the routing performance,this thesis studies the cooperation mechanisms for individual selfishness and social selfishness of node.For the individual selfishness,this thesis makes intensive study from the aspects of how to stimulate selfish nodes to forward messages quickly,reduce congestion and improve security.Based on above researches,for social selfishness,this thesis is made from the aspect of how to effectively stimulate the social selfish nodes of intra-group and inter-group to cooperatively forward messages.The detailed research contents are presented as follows:First of all,in order to solve the problem that current node cooperation mechanisms cannot effectively stimulate selfish nodes to quickly forward to reduce the message delivery delay,a virtual currency-based incentive-aware low delay node cooperation mechanism for DTNs is proposed to stimulate DTN selfish nodes to quickly forward message.A delay-based currency payment and allocation strategy is established to encourage selfish nodes to forward messages for other nodes quickly.In this way,the direct beneficial messages are forwarded to the nodes with smaller delivery delay and mutually beneficial messages are exchanged at the same time.A bargaining game model of alternating offers is established to determine the exchanged mutually beneficial messages.In addition,a greedy algorithm is proposed to solve the model's sub-game perfect equilibrium.Extensive simulations are carried out to verify the performance of the cooperation mechanism.Secondly,in order to solve the problem that current node cooperation mechanismscannot effectively stimulate the selfish nodes to cooperatively forward messages when congestions occur,a congestion-aware node cooperation mechanism for DTNs based on double auction is proposed.In the mechanism,nodes first calculate the expected value of messages based on the message delivery probability and node congestion degree.Then,nodes trade messages based on double auction model.By the message trade,the messages of a node with high connection degree will be forwarded to the node with high delivery probability and low connectivity degree,and finally forwarded to the destination node.A Bayesian game model of double auction trade process is established,and nodes get the optimal bid by solving the Bayesian equilibrium to trade messages.Extensive simulations are carried out to verify the performance of the cooperation mechanism over real-world dataset.Thirdly,in order to solve the problem that current node cooperation mechanisms cannot effectively resist various attacks maybe launched by selfish nodes,such as content modification,node insertion,node removal and message dropping,a secure and effective node cooperation mechanism for DTNs is proposed.A currency reward strategy based on probability increment is proposed to stimulate the selfish nodes to cooperatively forward messages according to the probability increment.The mechanism resists the content modification attack,node insertion attack,and node removal attack launched by selfish nodes,by combining with the meeting tickets and forwarding tickets.In addition,a check and punishment mechanism is used to detect whether the selfish nodes have dropped messages deliberately,so as to resist the message dropping attack.Extensive simulations are carried out to verify the performance of the mechanism in the routing and dissemination scenarios.Finally,in order to solve the problem that current node cooperation mechanisms for social selfishness cannot effectively stimulate the nodes of intra-group and inter-group to cooperatively forward messages,a social-aware node cooperation mechanism for DTNs is proposed.A currency reward scheme based on group probability increment is proposed to stimulate the inter-group nodes to cooperatively forward messages.An intra-group information sharing strategy is proposed to calculate the delivery probability of node,group delivery probability of node and inter-group delivery probability according to the shared information table.In addition,an intra-group node buffer sharing and cooperation strategy is also proposed to make the messages of a congested node be transferred to other nodes timely,to avoid being dropped due to limited buffer.Extensive simulations are carried out to verify the performance of the social-aware node cooperation mechanism in various scenarios.