Weathering the Storm: Managing Redundancy and Security in Ad Hoc Networks

Many ad hoc routing algorithms rely on broadcast flooding for location discovery or more generally for secure routing applications, particularly when dealing with Byzantine threats. 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 a broadcast storm in which the number of collisions is so large that we get system failure. Further reducing unnecessary transmissions greatly improves energy efficiency of such networks. Several variants have been proposed to reduce the relay overhead either deterministically or probabilistically. Gossip is a probabilistic algorithm, in which packet relaying is based on the outcome of coin tosses. The relay probability can be fixed, dynamic or adaptive. With dynamic Gossip, local information (local connectivity) is used. 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 gossiping is to minimize the number of relays, while retaining the main benefits of flooding, i.e., effective distance. In this paper we consider ways to reduce the number of redundant transmissions in broadcast flooding while guaranteeing security. We present several gossip type protocols, which exploit local connectivity and adaptively correct local relay failures. These use a (geodesic) cell based approach and preserve cell-distance. Our last two protocols are non probabilistic and guarantee delivery, the first such protocols to the best of our knowledge.