Research And Implementation On Data Fragmentation And Transmission Stra-Tegy In Layered Opportunistic Network

In opportunistic network, the nodes are not always keeping connection, they take advantage of nodes’ mobility to transmit messages. The opportunistic network does not need to complete end-to-end link, so we don’t have to set up communication facilities in advance, it has the advantages of networking simply and cost savings. The traditional communication system cannot meet the requirements in some scenes, for example, the basic communication facilities can’t be set up easily in complex environment or communication services are needed to deploy rapidly. Because of its unique advantages, the opportunistic network can play an important role in the above scenes. Based on existing research on opportunistic network, the improved key technology about data forwarding of opportunistic network is proposed and a set of layered opportunistic network testbed is implemented in this paper.Delivery ratio of large file transmission in opportunistic network is low for the characteristics of opportunistic network. In order to improve the ability of transferring large files, two kinds of data fragmentation strategies are proposed in this paper:fixed size data fragmentation strategy and variable size data fragmentation strategy. Two kinds of data fragmentation strategies have their respective advantages in different scenarios. Fixed size data fragmentation strategy is not only independent of the current networking state of communicating nodes in opportunistic network, but also independent of the encountering probability and connection duration between nodes in opportunistic network. So, fixed size data fragmentation strategy has stronger robustness, and is able to adapt to poorly reliable network scene. For the same size of data fragmentation, fixed size data fragmentation is suitable for copy control. The variable size data fragmentation strategy is based on historical statistic transmission rate and historical statistic connection duration between communicating nodes. The variable size data fragmentation strategy makes full use of current networking connection, minimizing the overhead caused by fragmentation control information. It is suitable for relatively reliable network environment.Hierarchical routing strategy with copy control make full use of community characteristics of opportunistic network. In this strategy, we set up a fixed node in each community which can communicate with each other directly and match data for nodes in community. And to take advantage of large encounter probability and long connection duration between two nodes in the same community, we take different transmission strategy according to if the source node and destination node is in the same community. At the same time, copy control mechanism is introduced in the strategy to reduce network overload.In this paper, a layered opportunistic network testbed is designed and implemented by realizing data fragmentation transmission function module and hierarchical routing function module. The testbed’s function is verified by multi-machine joint testing.