Global optimization of file availability through replication for efficient file sharing in MANETs

File sharing applications in mobile ad hoc networks (MANETs) have attracted more and more attention in recent years. The efficiency of file querying suffers from the distinctive properties of MANETs including node mobility and limited communication range and resource. An intuitive method to alleviate this problem is to create file replicas in the network. However, despite the efforts on file replication, no research has focused on the global optimal replica sharing with minimum average querying delay. Specifically, current file replication protocols in MANETs have two shortcomings. First, they lack a rule to allocate limited resource to different files in order to minimize the average querying delay. Second, they simply consider storage as resource for replicas, but neglect the fact that the file holders' frequency of meeting other nodes also plays an important role in determining file availability. A node having a higher meeting frequency with others provides higher availability to its files. In this paper, we introduce a new concept of resource for file replication, which considers both node storage and meeting frequency. We theoretically study the influence of resource allocation on the average querying delay and derive a resource allocation rule to minimize the average querying delay. We further propose a distributed file replication protocol that follows the rule. The trace-driven experiments on both the real-world GENI testbed and NS-2 show that our protocol can achieve shorter average querying delay at lower cost than current replication protocols, which justifies the correctness of our theoretical analysis and the effectiveness of the proposed protocol.