K-directory community: Reliable service discovery in MANET

Ensuring service availability is a key fault tolerance issue in service discovery for mobile ad hoc networks (MANET). Availability can be affected by sudden failure of service providers or directory nodes or even by network disconnection due to node mobility. So, to ensure network-wide service availability, services must be replicated cautiously, so that, the storage, update and discovery costs can be minimized. Achieving service availability in a resource efficient manner is both desirable and challenging in MANET. Existing works have not addressed these issues adequately. In this paper, we propose a distributed directory-based service discovery protocol (SDP) for MANET which works by electing the top KK directory nodes considering rich resources. Resource-based election ensures high reliability for the directory nodes. The community of directory nodes then divides itself into multiple quorums. Services registered with a directory are replicated among its quorum members. This approach, while controlling replication and update costs, can guarantee network-wide service availability by the quorum intersection property. To further reduce the service discovery cost, we divide the entire network into one or more tree-structured domains. Since, the KK-directory community is the heart of our approach, to keep the directory community intact, we consider substituting failed directories using an incremental election policy. Our protocol can also cope with dynamic and frequent topological changes caused by network partitioning as well as partition merges. To evaluate the performance of our proposed protocol, we have conducted extensive simulations and developed a prototype system. The results show that, compared with similar works, our protocol significantly reduces message cost and discovery delay, while improving system robustness.