Probabilistic quorum systems in wireless ad hoc networks

Abstract

Quorums are a basic construct in solving many fundamental distributed computing problems. One of the known ways of making quorums scalable and efficient is by weakening their intersection guarantee to being probabilistic. This paper explores several access strategies for implementing probabilistic quorums in ad hoc networks. In particular, we present the first detailed study of asymmetric probabilistic bi-quorum systems, that allow to mix different access strategies and different quorums sizes, while guaranteeing the desired intersection probability. We show the advantages of asymmetric probabilistic bi-quorum systems in ad hoc networks. Such an asymmetric construction is also useful for other types of networks with non uniform access costs (e.g, peer-to-peer networks). The paper includes both a formal analysis of these approaches backed up by an extensive simulation based study. In particular, we show that one of the strategies that uses Random Walks, exhibits the smallest communication overhead, thus being very attractive for ad hoc networks.

Accessing probabilistic quorums in dynamic networks

“…In [8], the authors studied combinations of the above access schemes for probabilistic quorums. The network topology is modeled by a random geometric graph.…”

“…The main schemes of accessing probabilistic quorums are through direct sampling, view-based or by flooding [8].…”

“…In [8], it was shown that random walk is an efficient scheme to access probabilistic quorums for static networks. The random walk makes a necessary number of steps to reach a uniform distribution (i.e., there is an equal probability of being at any particular vertex), and then returns a sample to a client wishing to access a quorum.…”

“…In particular, probabilistic quorums have shown to be scalable, efficient, and suitable for dynamic environments [12]. Unfortunately, most existent analytic results for accessing probabilistic quorums are tailored to static networks [8]. However, we believe that the correct functioning of such systems must be assured in a much wider range of scenarios.…”

Relaxing data consistency along different dimensions for increasing operation availabilities

“…Merideth and Reiter introduced probabilistic opaque quorum systems [17] to tolerate more Byzantine failures than the classical PQSs. Another type of PQSs is introduced by Friedman et al for tolerating dynamic failures in ad hoc networks and managing replicated data without any geographical information [6].…”