Hybrid cache invalidation schemes in mobile environments

To make cached data consistent, the server periodically broadcasts an invalidation report to all mobile clients in its cell so that each can invalidate obsolete data items from its local cache. We present two hybrid cache invalidation schemes: Hybrid cache invalidation with simple broadcasting (HSB), and hybrid cache invalidation with attribute bit sequence broadcasting (HABSB). In these schemes the server is stateful as it stores the caching information of each mobile client in its cell to allow for long disconnections. However, the server periodically broadcasts an invalidation report similar to a stateless server. In HABSB, attribute bit sequences are added in each broadcasted invalidation report to maximize the cache-hit ratio and to reduce the data transmission of queried data items. The simulation results show that HSB and HABSB can significantly reduce the bandwidth requirement, and HABSB is very efficient in improving mobile caching.