Cost efficient broadcast based cache invalidation for mobile environments

To improve the performance of mobile computers, a number of broadcast based cache invalidation schemes have been proposed in the past to support object locality. However most of these schemes have focused on providing support for client disconnection and reducing query delay. The size of invalidation reports and the effect of invalidating items cached by many clients are also important issues that must be addressed in order to provide cost-efficient cache invalidation in a mobile environment. In this paper, we propose two techniques, Validation-Invalidation Reports (VIR) and the Delayed Requests Scheme (DRS) to address these issues. VIR uses a combination of validation and invalidation reports, allowing the server to construct and broadcast smaller reports at each interval, thus improving downlink channel utilization. DRS addresses the problem where multiple clients request for the same data items. It introduces a "cool down" period after an invalidation, to reduce the number of uplink requests sent by clients. Simulation results show that compared to the original TS approach [1], the proposed schemes lower transmission cost associated with cache invalidation by between 5%-25% in the downlink channel and between 10%-40% in the uplink channel.