Study On Data Dissemination Mchamisms In Wireless Networks With Intermittent Connectivity Characteristic

In some emerging wireless networks,the connectivity betweed nodes is often intermittent,such as mobile computing environment and delay and disruption tolerant networks. This new characteristic makes many applications under this environment face many different challenges from traditional wired networks. To study how to face these challenges has important scientific and economic significance. Data dissemination is a main method to share and transmit data among nodes,so how to design data dissemination mechanisms adapt to intermittently connected environment is important for data sharing in such networks. This paper proposed the efficient data dissemination mechanisms for mobile computing environment and delay and disruption tolerant networks respectively.In mobile computing environment, as the need for data management and dissemination, mobile database technology emerged. But because the intermittent connectivity characteristic of this environment, the data consistency between mobile clients and servers is always deviation,and the data synchronization is one of the most important methods to maintain the data consistency between mobile clients and servers. In order to improve the data synchronization performance of mobile database, a new synchronization granularity based on related transaction results is proposed. This new granularity can greatly decrease the amount of data transfer and utilize the valuable wireless radio resources efficiently. Further, a cross-layer method is proposed, which can set proper committed data volume depending on real network conditions. Experiments show, by using this method , rollback times due to network disconnection can be reduced remarkably. The results further show,by using the proposed two schemes together, there is a 42% increase of the average synchronization throughput.A data dissemination algorithm based on content classification for delay and disruption tolerant networks is proposed. The algorithm manages the node’s buffer based on the data’s content popularity to guarantee benefits of most nodes when there is no enough buffer space. Further, it deletes copies of messages selectively according to the receiving time of subscription to favor minority nodes. The analytical and simulation results show that the algorithm can allocate the cache resources according to need and guarantee a high degree of delivery while maintaining low levels of delivery latencies and overhead when buffer resource is not enough. In addition, a fragmentation method based on erasure-coding is proposed to solve the disorder problem of fragments, and further improve the performance of the data dissemination.There is no central node or central node will not be achieved due to network disconnection, so an absolute distributed secure data dissemination mechanism for delay and disruption tolerant networks is proposed. The mechanism adopts a distributed identity-based authenticated method, which is no need for a central Private Key Generator. Besides, depending on threshold cryptography and the mapping from category name to category key, the node only needs to communicate with random neighbor nodes whose number is no less than a certain threshold, and then it can acquire the data category key. Analytical and simulation results show this mechanism can guarantee the security requirements and greatly improve the efficiency of obtaining keys. Compared to method based on mobile key server, the efficiency of obtaining keys can be improved 88.6% at best and the delay can be reduced 92.1% at most,so it suits DTN very well.