Disseminating Updates to Mobile Clients

In this paper, we address the problem of propagating data updates to a large number of mobile clients. Typically, mobile clients operate autonomously, i.e., disconnected from data servers, for prolonged periods of time relying on locally replicated corporate data (e.g., database views, file systems). From time to time, they need to refresh their replicas with data changes registered at a central data repository. We propose a hybrid approach for delivering these updates to the clients. We use a broadcast channel to “cache on the air” fresh updates for as long as they are high on demand. At the same time, any requests for older updates are individually serviced by the server through a separate channel. The air-caching satisfies the bulk of clients’ needs, increasing data throughput many-fold compared to traditional data delivery mechanisms. We describe a hierarchical air-cache structure, and analyze the performance of broadcasting a log of committed updates. Based on that, we propose a technique that dynamically modifies the contents and the structure of the air-cache according to the number and the (dis)connection habits of the clients. Through extensive simulations, we demonstrate the adaptiveness, efficiency, and practicality of the proposed system even for very large client populations. ∗This work was supported by the Center for Satellite and Hybrid Communication Networks, under NASA cooperative agreement NCC3-528