A Selective Push Algorithm for Cooperative Cache Consistency Maintenance over MANETs

Cooperative caching is an important technique to support efficient data dissemination and sharing in Mobile Ad hoc Networks (MANETs). In order to ensure valid data access, the cache consistency must be maintained properly. Many existing cache consistency maintenance algorithms are stateless, in which the data source node is unaware of the cache status at each caching node. Even though stateless algorithms do not pay the cost for cache status maintenance, they mainly rely on broadcast mechanisms to propagate the data updates, thus lacking cost-effectiveness and scalability. Besides stateless algorithms, stateful algorithms can significantly reduce the consistency maintenance cost by maintaining status of the cached data and selectively propagating the data updates. Stateful algorithms are more effective in MANETs, mainly due to the bandwidth-constrained, unstable and multi-hop wireless communication. In this paper, we propose a stateful cache consistency maintenance algorithm called Greedy Walk-based Selective Push (GWSP). In GWSP, the data source node maintains the Time-to-Refresh value and the cache query rate associated with each cache copy. Thus, the data source node propagates the source data update only to caching nodes which are in great need of the update. After recipients of the source data update have been decided, GWSP employs a greedy but efficient strategy to propagate the update among the selected caching nodes. Extensive simulations are conducted to evaluate the performance of GWSP. The evaluation results show that, compared with the widely used Pull with Dynamic TTR algorithm, GWSP can save up to 41% traffic overhead and reduce the query latency by up to 85% for cache consistency maintenance in cooperative caching over MANETs.