Probabilistic Discovery of Semantically Diverse Content in MANETs

Mobile ad hoc networks rely on the opportunistic interaction of autonomous nodes to form networks without the use of infrastructure. Given the radically decentralized nature of such networks, their potential for autonomous communication is significantly improved when the need for a priori consensus among the nodes is kept to a minimum. This paper addresses an issue within the domain of semantic content discovery, namely, its current reliance on the preexisting agreement between the schema of content providers and consumers. We present OntoMobil, a semantic discovery model for ad hoc networks that removes the assumption of a globally known schema and allows nodes to publish information autonomously. The model relies on the randomized dissemination and replication of metadata through a gossip protocol. Given schemas with partial similarities, the randomized metadata dissemination mechanism facilitates eventual semantic agreement and provides a substrate for the scalable discovery of content. A discovery protocol can then utilize the replicated metadata to identify content within a predictable number of hops using semantic queries. A stochastic analysis of the gossip protocol presents the different trade-offs between discoverability and replication. We evaluate the proposed model by comparing OntoMobil against a broadcast-based protocol and demonstrate that semantic discovery with proactive replication provides good scalability properties, resulting in a high discovery ratio with less overhead than a reactive nonreplicated discovery approach.