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Many Random Walks Are Faster Than One
"... We pose a new and intriguing question motivated by distributed computing regarding random walks on graphs: How long does it take for several independent random walks, starting from the same vertex, to cover an entire graph? We study the cover time–the expected time required to visit every node in a ..."
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Cited by 45 (3 self)
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We pose a new and intriguing question motivated by distributed computing regarding random walks on graphs: How long does it take for several independent random walks, starting from the same vertex, to cover an entire graph? We study the cover time–the expected time required to visit every node in a graph at least once–and we show that for a large collection of interesting graphs, running many random walks in parallel yields a speedup in the cover time that is linear in the number of parallel walks. We demonstrate that an exponential speedup is sometimes possible, but that some natural graphs allow only a logarithmic speedup. A problem related to ours (in which the walks start from some probabilistic distribution on vertices) was previously studied in the context of space efficient algorithms for undirected stconnectivity and our results yield, in certain cases, an improvement upon some of the earlier bounds.
Brahms: Byzantine Resilient Random Membership Sampling
, 2008
"... We present Brahms, an algorithm for sampling random nodes in a large dynamic system prone to malicious behavior. Brahms stores small membership views at each node, and yet overcomes Byzantine attacks by a linear portion of the system. Brahms is composed of two components. The first one is a resilien ..."
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Cited by 45 (2 self)
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We present Brahms, an algorithm for sampling random nodes in a large dynamic system prone to malicious behavior. Brahms stores small membership views at each node, and yet overcomes Byzantine attacks by a linear portion of the system. Brahms is composed of two components. The first one is a resilient gossipbased membership protocol. The second one uses a novel memoryefficient approach for uniform sampling from a possibly biased stream of ids that traverse the node. We evaluate Brahms using rigorous analysis, backed by simulations, which show that our theoretical model captures the protocol’s essentials. We study two representative attacks, and show that with high probability, an attacker cannot create a partition between correct nodes. We further prove that each node’s sample converges to a uniform one over time. To our knowledge, no such properties were proven for gossip protocols in the past.
Gossiping in Distributed Systems
"... Gossipbased algorithms were first introduced for reliably disseminating data in largescale distributed systems. However, their simplicity, robustness, and flexibility make them attractive for more than just pure data dissemination alone. In particular, gossiping has been applied to data aggregatio ..."
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Cited by 40 (0 self)
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Gossipbased algorithms were first introduced for reliably disseminating data in largescale distributed systems. However, their simplicity, robustness, and flexibility make them attractive for more than just pure data dissemination alone. In particular, gossiping has been applied to data aggregation, overlay maintenance, and resource allocation. Gossiping applications more or less fit the same framework, with often subtle differences in algorithmic details determining divergent emergent behavior. This divergence is often difficult to understand, as formal models have yet to be developed that can capture the full design space of gossiping solutions. In this paper, we present a brief introduction to the field of gossiping in distributed systems, by providing a simple framework and using that framework to describe solutions for various application domains.
RAPID: Reliable Probabilistic Dissemination in wireless adhoc networks
 In Proceedings of the 26th IEEE International Symposium on Reliable Distributed Systems (SRDS
, 2007
"... Reliable broadcast is a basic service for many collaborative applications as it provides reliable dissemination of the same information to many recipients. In this paper we propose a novel ReliAble ProbabIlistic Dissemination protocol, called RAPID, for mobile wireless adhoc networks that tolerates ..."
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Cited by 24 (4 self)
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Reliable broadcast is a basic service for many collaborative applications as it provides reliable dissemination of the same information to many recipients. In this paper we propose a novel ReliAble ProbabIlistic Dissemination protocol, called RAPID, for mobile wireless adhoc networks that tolerates message omissions, node crashes, and selfish behavior. The protocol employs a combination of probabilistic forwarding with deterministic corrective measures. The forwarding probability is set based on the observed number of nodes in each onehop neighborhood, while the deterministic corrective measures include deterministic gossiping as well as timer based corrections of the probabilistic process. These aspects of the protocol are motivated by a theoretical analysis that is also presented in the paper, which explains why this unique protocol design is inherent to adhoc networks environments. Since the protocol only relies on local computations and probability, it is highly resilient to mobility and failures. By adding authentication, it can even be made malicious tolerant. Additionally, the paper includes a detailed performance evaluation by simulation. We compare the performance and the overhead of RAPID with the performance of other probabilistic approaches. Our results show that RAPID achieves a significantly higher node coverage with a smaller overhead.
Gossiping on MANETs: The Beauty and the Beast
 ACM Operating Systems Review
"... Gossip protocols have emerged as a powerful technique for implementing highly scalable and robust services, such as information dissemination and aggregation. The fact that gossip protocols require very little or no structure to operate makes them particularly appealing to apply in dynamic systems, ..."
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Cited by 18 (2 self)
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Gossip protocols have emerged as a powerful technique for implementing highly scalable and robust services, such as information dissemination and aggregation. The fact that gossip protocols require very little or no structure to operate makes them particularly appealing to apply in dynamic systems, where topology changes are common (for instance, due to frequent faults or high churn rates). Therefore, gossip protocols seem particularly well fit to operate in wireless selforganizing networks. Unfortunately, these networks have a number of characteristics that impede the deployment of gossip protocols designed for wired networks. In this work we identify the inherent differences in communication between wired and wireless networks and their impact on the design and implementation of gossip protocols. In particular, our comparison includes drawing a distinction between the gossiping primitives suitable for each of these environments. In the context of this analysis, we conclude by presenting a list of open research questions. 1.
Formal Analysis Techniques for Gossiping Protocols
 ACM SIGOPS Oper. Syst. Rev.
, 2007
"... We give a survey of formal verification techniques that can be used to corroborate existing experimental results for gossiping protocols in a rigorous manner. We present properties of interest for gossiping protocols and discuss how various formal evaluation techniques can be employed to predict the ..."
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Cited by 14 (4 self)
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We give a survey of formal verification techniques that can be used to corroborate existing experimental results for gossiping protocols in a rigorous manner. We present properties of interest for gossiping protocols and discuss how various formal evaluation techniques can be employed to predict them.
A Partitiontolerant Manycast Algorithm for Disaster Area Networks
"... Abstract—Information dissemination in disaster scenarios requires timely and energyefficient communication in intermittently connected networks. When the existing infrastructure is damaged or overloaded, we suggest the use of a manycast algorithm that runs over a wireless mobile ad hoc network, and ..."
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Cited by 14 (9 self)
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Abstract—Information dissemination in disaster scenarios requires timely and energyefficient communication in intermittently connected networks. When the existing infrastructure is damaged or overloaded, we suggest the use of a manycast algorithm that runs over a wireless mobile ad hoc network, and overcomes partitions using a storeandforward mechanism. This paper presents a random walk gossip protocol that uses an efficient data structure to keep track of already informed nodes with minimal signalling. Avoiding unnecessary transmissions also makes it less prone to overloads. Experimental evaluation shows higher delivery ratio, lower latency, and lower overhead compared to a recently published algorithm. I.
A Survey of Distributed Data Aggregation Algorithms,” University of Minho
, 2011
"... Distributed data aggregation is an important task, allowing the decentralized determination of meaningful global properties, that can then be used to direct the execution of other applications. The resulting values result from the distributed computation of functions like count, sum and average. S ..."
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Cited by 10 (1 self)
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Distributed data aggregation is an important task, allowing the decentralized determination of meaningful global properties, that can then be used to direct the execution of other applications. The resulting values result from the distributed computation of functions like count, sum and average. Some application examples can found to determine the network size, total storage capacity, average load, majorities and many others. In the last decade, many different approaches have been proposed, with different tradeoffs in terms of accuracy, reliability, message and time complexity. Due to the considerable amount and variety of aggregation algorithms, it can be difficult and time consuming to determine which techniques will be more appropriate to use in specific settings, justifying the existence of a survey to aid in this task. This work reviews the state of the art on distributed data aggregation algorithms, providing three main contributions. First, it formally defines the concept of aggregation, characterizing the different types of aggregation functions. Second, it succinctly describes the main aggregation techniques, organizing them in a taxonomy. Finally, it provides some guidelines toward the selection and use of the most relevant techniques, summarizing their principal characteristics. 1
Probabilistic quorum systems in wireless ad hoc networks
 In Proceedings of the 38th IEEE International Conference on Dependable Systems and Networks (DSNDCCS
, 2008
"... 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 q ..."
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Cited by 9 (4 self)
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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 biquorum 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 biquorum systems in ad hoc networks. Such an asymmetric construction is also useful for other types of networks with non uniform access costs (e.g, peertopeer 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. Categories and Subject Descriptors: C.2.1 [Comp.Communication Networks]: Network Architecture and Design—Wireless communication;
Correctness of GossipBased Membership under Message Loss
"... Due to their simplicity and effectiveness, gossipbased membership protocols have become the method of choice for maintaining partial membership in large P2P systems. A variety of gossipbased membership protocols were proposed. Some were shown to be effective empirically, lacking analytic understan ..."
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Cited by 8 (2 self)
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Due to their simplicity and effectiveness, gossipbased membership protocols have become the method of choice for maintaining partial membership in large P2P systems. A variety of gossipbased membership protocols were proposed. Some were shown to be effective empirically, lacking analytic understanding of their properties. Others were analyzed under simplifying assumptions, such as lossless and delayless network. It is not clear whether the analysis results hold in dynamic networks where both nodes and network links can fail. In this paper we try to bridge this gap. We first enumerate the desirable properties of a gossipbased membership protocol, such as view uniformity, independence, and load balance. We then propose a simple Send & Forget protocol, and show that even in the presence of message loss, it achieves the desirable properties.