Adaptive gossip protocols: Managing security and redundancy in dense ad hoc networks

Many ad hoc routing algorithms rely on broadcast flooding for location discovery or, more generally, for secure routing applications. Flooding is a robust algorithm but because of its extreme redundancy, it is impractical in dense networks. Indeed in large wireless networks, the use of flooding algorithms may lead to broadcast storms where the number of collisions is so large that it causes system failure. To prevent broadcast storms, many mechanisms that reduce redundant transmissions have been proposed that reduce retransmission overhead either deterministically or probabilistically. Gossip is a probabilistic algorithm in which packet retransmission is based on the outcome of coin tosses. The retransmission probability can be fixed, dynamic or adaptive. With dynamic gossip, local information is used to decide on retransmission probability. With adaptive gossip, the decision to relay is adjusted adaptively based on the outcome of coin tosses, the local network structure, and the local response to the flooding call. The goal of gossip is to minimize the number of retransmissions, while retaining the main benefits of flooding, e.g., universal coverage, minimal state retention, and path length preservation. In this paper we consider ways to reduce the number of redundant transmissions in flooding while guaranteeing security. We present several new gossip protocols that exploit local connectivity to adaptively correct propagation failures and protect against Byzantine attacks. A main contribution of this work is that we introduce a cell-grid approach that allows us to analytically prove performance and security protocol properties. The last two gossip protocols that we give are fully adaptive, i.e., they automatically correct all faults and guarantee delivery, the first such protocols to the best of our knowledge.