SSUM: Smart Server Update Mechanism for Maintaining Cache Consistency in Mobile Environments

This paper proposes a cache consistency scheme based on a previously proposed architecture for caching database data in MANETs. The original scheme for data caching stores the queries that are submitted by requesting nodes in special nodes, called query directories (QDs), and uses these queries to locate the data (responses) that are stored in the nodes that requested them, called caching nodes (CNs). The consistency scheme is server-based in which control mechanisms are implemented to adapt the process of caching a data item and updating it by the server to its popularity and its data update rate at the server. The system implements methods to handle disconnections of QD and CN nodes from the network and to control how the cache of each node is updated or discarded when it returns to the network. Estimates for the average response time of node requests and the average node bandwidth utilization are derived in order to determine the gains (or costs) of employing our scheme in the MANET. Moreover, ns2 simulations were performed to measure several parameters, like the average data request response time, cache update delay, hit ratio, and bandwidth utilization. The results demonstrate the advantage of the proposed scheme over existing systems.