| The proliferation of mobile devices has made mobile data management a hot topic in recent mobile computing research. One of the most challenging objectives of mobile data management is the vision of data access from anywhere at any time. Due to the special characteristics of mobile environment, mainly variable even absent network connection and the frequent unavailability of access to mobile devices, this vision becomes extraordinarily difficult relative to fixed, wired network computing. An optimistic data replication is a generally agreed upon method to alleviate the adverse mobile environment. However, the two currently most popular models, the Client/Server and Peer-to-Peer models, do not meet the need very well for this purpose in many aspects, such as data spectrum, communication mechanisms and simplicity. To address these challenges, in our research, we proposed an application transparent, double middleware-based software architecture. One logical mobile server is first introduced to provide highly available data service, which often cannot be met by mobile devices. Two middlewares, Mobile-Mobile Environment Manager (M-MEM) and Fixed-Mobile Environment Manager (F-MEM), are instrumented into mobile device and the highly available mobile server, respectively. The combination of M-MEM and F-MEM has taken the advantages of both the Client/Server model and the Peer-to-Peer model. In the new architecture, the data spectrum is extended to any file in mobile devices. Data are selected to be under the control of the mobile data service system, according to its activeness from the mobile user's behavior. Active data are transparently and automatically replicated among multiple heterogeneous devices along the mobile user through the highly available F-MEM. Data consistency among multiple replicas is automatically maintained by the system without user intervention. The update propagation is based on a combination of PUSH and PULL models. Data and control communication is through an XML-based protocol to meet the needs of the heterogeneous platforms, from both the hardware and software sense, of mobile devices. The security of communication is ensured by a PGP based public key encryption system. A reliable, asynchronous message computing-based model is used in our architecture to address the issues in the mobile environment, such as the intermittent network connection and low bandwidth. To adapt to the mobile network, two techniques are employed. First, the data and control request are optimized to minimize the potential communication. Second, for the inevitable network traffic, an incremental update-based mobile network traffic adaptor is employed to reduce the communication content. To validate the architecture, both trace driven-based simulation and synthetic user-based testing are employed. Trace-based simulation is used to refine the system and various experiments. Synthetic user simulation is extensively used to test the robustness of the system. |
