Mobile Database Application In Ad Hoc Network

The traditional mobile database model mainly includes the server, mobile support node and the mobile computer, which has such characteristics as the location of the mobile node mobility, network communication asymmetry, network disconnection frequently, mobile node storage capacity and processing capacity limitation,and so on. However, networks based on the traditional mobile database model have a large number of base stations, mobile switching center and other basic communication equipment, besides they are usually constructed around the city, so they don’t need to consider mostly the influence of environmental factors. However, Ad hoc network is a multi-hop, no center, self-organizing wireless network. Because of considering many factors such as environment is not conducive to the laying of foundation facilities or infrastructure damage, and so on, Ad hoc network is used. In reality, Ad hoc network is a typical application such as fieldworks of investigative teams, disaster relief, mineral exploration, and so on. In Ad hoc network, we should consider that the energy, storage capacity and bandwidth of mobile computer is limited, and mobile computer is disconnected from network frequently, and other reasons, traditional mobile database model is applied to the Ad hoc network will cause many problems, so traditional mobile database model needs to be improved in order to meet the Ad hoc network.In view of the problems that are traditional mobile database model can not adapt to the actual conditions of Ad hoc network, the main work of this paper includes:(1) we improved the traditional mobile database model with adding a local server as the agent to adapt to the situation of Ad hoc network, forming MDAN(Mobile database in ad hoc network) model which comprises mobile computer, local server and master server. Then, the MDAN model’s characteristics and working mode were described in detail. Then, I propose to the method of data consistency maintenance. Meanwhile, I put forward to the method of selecting the local server and the strategy of replacing cache data of mobile computer. (2) The solutions of two problems in MDAN model are raised. One is to data conflicts when mobile computers apply data from local server, another is to make a decision about transactions using to outdated data whether to make transactions redoing. For the first problem, transactions are classified by priority level in order to decide to the sequence of using data about transactions; and designing the priority queue is to manage transactions which apply data in failure. In addition, in order to avoid deadlock caused by lots of data conflict, I give the concept of transaction application data conflict probability and the method of how to undo the deadlock. For the second problem, firstly, the method about detecting transactions using to outdated data is proposed; Then, in the case of network connection, the problem about transactions using to outdated data whether to make transactions redoing are classified to discuss; Then, in the case of network disconnection, the problem about transactions using to outdated data whether to make transactions redoing are classified to discuss. Finally, by means of specific experimental data of simulation experiments, the feasibility of designing algorithms for MDAN model and mobile database system stability are proved further.