Sponsored by NASA 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 le 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 satis es 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 modi es 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 e ciency 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 NCC and partially sponsored by Hughes Network Systems under contract No on Wireless Networks and Direct Broadcast Satellite Systems