Rcsearch And Improvement On Probabilistic Routing In Delay Tolerant Network

In certain circumstances, such as wildlife tracking, ocean exploration, satellite communication, remote region communication, etc., network is easy to appear the phenomenon of partitioning(disconnected), then no stable end-to-end links could be established between two nodes. The message can only be transmitted through the intermittent links, therefore the traditional network architecture can not be applied to these special circumstances. To achieve the communication in above occasions, Kevin Fall and other scientists proposed a general overlay network architecture at the SIGCOMM international conference in2003, called DTN (DTN:Delay Tolerant Network). DTN use the store-carry-forward scheme, where nodes can forward packets to their destination through intermittent links under the limited network environment.The routing protocols in DTN are divided into two types:single-copy routing protocol and multi-copy routing protocol. Multi-copy routing could delivery the message to destination nodes with a higher probability than single-copy routing, so the research about the multi-copy routing has become a hot topic. Probabilistic routing protocol is a typical multi-copy routing protocol, it through the encounter history information between the node and the destination node to represent the probability of successful delivery. When two nodes meet, they will determine whether to forward packets to the peer node according to this probability.Probabilistic routing protocol still brings two problems, network congestion and the deviation of history information. The probabilistic routing protocol of the DTN brings a large number of message copies, thus it is necessary to set an efficient congestion control scheme to relieve the congestion. Besides, the encounter probability between nodes could not accurately indicate the possibility of the successful message delivery, but indirectly infer the probability of message delivery to the destination node. At present, no valid physical parameter in the network could accurately indicate the possibility of the successful delivery, the possibility that message delivery successfully to destination is inferred according to the encounter probability, so it is necessary to get a more reasonable method to infer the probability and improve the accuracy of the history information.In this paper, the research background, characteristics, network architecture, application about DIN are firstly introduced, analysis and summary of the several typical routing protocols are presented, especially the probability routing protocol. Then the improvement scheme of the probability routing is proposed:1. The probabilistic routing protocol of the DTN brings a large number of message copies. In this paper, to solve the problem of congestion caused by the large number of message copies, the congestion degree of the node is estimated according to congestion time, a new probability called delivery probability of message is signified based on both the encounter probability and congestion degree. When the nodes met with each other, the judgment whether the message should be sent to the other node would be made according to the new probability. As the result, the influence of congestion on the probabilistic routing could be efficiently averted.2. The probability of two nodes encounter could not accurately indicate the probability that message delivery successfully to destination, indirect deduction cause the lack of accuracy in history information. In this paper, the probabilistic routing protocol would be combined with characteristics of ant colony algorithm. The more pheromone on links the more selected possibility would be brought. The pheromone on selected link would increase after ant passed, otherwise the pheromone would reduce. In this improvement scheme, a new probability called selection probability is signified based on both the encounter probability and selection mechanism. When the nodes met with each other, the judgment whether the message should be sent to the other node would be made according to the new probability. As the result, the lack of accuracy in history information could be efficient improved.3. The ONE simulator is employed to make simulation experiment on the improvement scheme of probabilistic routing protocol, and the analysis and compare of simulation results would be showed in this paper.