Results 1  10
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75
GeoQuorums: Implementing Atomic Memory in Mobile Ad Hoc Networks
, 2004
"... We present a new approach, the GeoQuorums approach, for implementing atomic read/write shared memory in mobile ad hoc networks. Our approach is based on associating abstract atomic objects with certain geographic locations. We assume the existence of focal points, geographic areas that are normall ..."
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Cited by 56 (13 self)
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We present a new approach, the GeoQuorums approach, for implementing atomic read/write shared memory in mobile ad hoc networks. Our approach is based on associating abstract atomic objects with certain geographic locations. We assume the existence of focal points, geographic areas that are normally "populated" by mobile nodes.
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 46 (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.
On the cover time and mixing time of random geometric graphs
 Theor. Comput. Sci
, 2007
"... The cover time and mixing time of graphs has much relevance to algorithmic applications and has been extensively investigated. Recently, with the advent of adhoc and sensor networks, an interesting class of random graphs, namely random geometric graphs, has gained new relevance and its properties ..."
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Cited by 41 (2 self)
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The cover time and mixing time of graphs has much relevance to algorithmic applications and has been extensively investigated. Recently, with the advent of adhoc and sensor networks, an interesting class of random graphs, namely random geometric graphs, has gained new relevance and its properties have been the subject of much study. A random geometric graph G(n, r) is obtained by placing n points uniformly at random on the unit square and connecting two points iff their Euclidean distance is at most r. The phase transition behavior with respect to the radius r of such graphs has been of special interest. We show that there exists a critical radius ropt such that for any r ≥ ropt G(n, r) has optimal cover time of Θ(n log n) with high probability, and, importantly, ropt = Θ(rcon) where rcon denotes the critical radius guaranteeing asymptotic connectivity. Moreover, since a disconnected graph has infinite cover time, there is a phase transition and the corresponding threshold width is O(rcon). On the other hand, the radius required for rapid mixing rrapid = ω(rcon), and, in particular, rrapid = Θ(1/poly(log n)). We are able to draw our results by giving a tight bound on the electrical resistance and conductance of G(n, r) via certain constructed flows.
Virtual mobile nodes for mobile ad hoc networks
 in DISC04
, 2004
"... Abstract. One of the most significant challenges introduced by mobile networks is coping with the unpredictable motion and the unreliable behavior of mobile nodes. In this paper, we define the Virtual Mobile Node Abstraction, which consists of robust virtual nodes that are both predictable and relia ..."
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Cited by 40 (14 self)
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Abstract. One of the most significant challenges introduced by mobile networks is coping with the unpredictable motion and the unreliable behavior of mobile nodes. In this paper, we define the Virtual Mobile Node Abstraction, which consists of robust virtual nodes that are both predictable and reliable. We present the Mobile Point Emulator, a new algorithm that implements the Virtual Mobile Node Abstraction. This algorithm replicates each virtual node at a constantly changing set of real nodes, modifying the set of replicas as the real nodes move in and out of the path of the virtual node. We show that the Mobile Point Emulator correctly implements a virtual mobile node, and that it is robust as long as the virtual node travels through wellpopulated areas of the network. The Virtual Mobile Node Abstraction significantly simplifies the design of efficient algorithms for highly dynamic mobile ad hoc networks. 1
Pilot: Probabilistic Lightweight Group Communication System for Ad Hoc Networks
 IEEE Transactions on Mobile Computing
, 2004
"... Providing reliable group communication is an ever recurring topic in distributed settings. In mobile ad hoc networks, this problem is even more significant since all nodes act as peers, while it becomes more challenging due to highly dynamic and unpredictable topology changes. In order to overcome ..."
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Cited by 39 (3 self)
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Providing reliable group communication is an ever recurring topic in distributed settings. In mobile ad hoc networks, this problem is even more significant since all nodes act as peers, while it becomes more challenging due to highly dynamic and unpredictable topology changes. In order to overcome these difficulties, we deviate from the conventional point of view, i.e., we "fight fire with fire," by exploiting the nondeterministic nature of ad hoc networks. Inspired by the principles of gossip mechanisms and probabilistic quorum systems, we present in this paper PILOT (ProbabilistIc Lightweight grOup communication sysTem) for ad hoc networks, a twolayer system consisting of a set of protocols for reliable multicasting and data sharing in mobile ad hoc networks. The performance of PILOT is predictable and controllable in terms of both reliability (fault tolerance) and efficiency (overhead). We present an analysis of PILOT's performance, which is used to finetune protocol parameters to obtain the desired trade off between reliability and efficiency. We confirm the predictability and tunability of PILOT through simulations with ns2.
RaWMS  Random Walk based Lightweight Membership Service for Wireless Ad Hoc Networks
, 2006
"... This paper presents RaWMS, a novel lightweight random membership service for ad hoc networks. The service provides each node with a partial uniformly chosen view of network nodes. Such a membership service is useful, e.g., in data dissemination algorithms, lookup and discovery services, peer samplin ..."
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Cited by 38 (8 self)
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This paper presents RaWMS, a novel lightweight random membership service for ad hoc networks. The service provides each node with a partial uniformly chosen view of network nodes. Such a membership service is useful, e.g., in data dissemination algorithms, lookup and discovery services, peer sampling services, and complete membership construction. The design of RaWMS is based on a random walk (RW) sampling technique. The paper includes a formal analysis of both the RW sampling technique and RaWMS and verifies it through a detailed simulation study. In addition, RaWMS is compared both analytically and by simulations with a number of other known methods such as flooding and gossipbased techniques.
The Power of Choice in Random Walks: An Empirical Study
 In MSWiM
, 2006
"... In recent years randomwalkbased algorithms have been proposed for a variety of networking tasks. These proposals include searching, routing, selfstabilization, and query processing in wireless networks, peertopeer networks and other distributed systems. This approach is gaining popularity becau ..."
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Cited by 24 (0 self)
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In recent years randomwalkbased algorithms have been proposed for a variety of networking tasks. These proposals include searching, routing, selfstabilization, and query processing in wireless networks, peertopeer networks and other distributed systems. This approach is gaining popularity because random walks present locality, simplicity, lowoverhead and inherent robustness to structural changes. In this work we propose and investigate an enhanced algorithm that we refer to as random walks with choice. In this algorithm, instead of selecting just one neighbor at each step, the walk moves to the next node after examining a small number of neighbors sampled at random. Our empirical results on random geometric graphs, the model best suited for wireless networks, suggest a significant improvement in important metrics such as the cover time and loadbalancing properties of random walks. We also systematically investigate random walks with choice on networks with a square grid topology. For this case, our simulations indicate that there is an unbounded improvement in cover time even with a choice of only two neighbors. We also observe a large reduction in the variance of the cover time, and a significant improvement in visit load balancing.
A Survey of Dependability Issues in Mobile Wireless Networks
, 2003
"... this article is organized as follows ..."
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On the Cover Time of Random Geometric Graphs
 In: ICALP. (2005
, 2005
"... Abstract. The cover time of graphs has much relevance to algorithmic applications and has been extensively investigated. Recently, with the advent of adhoc and sensor networks, an interesting class of random graphs, namely random geometric graphs, has gained new relevance and its properties have be ..."
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Cited by 22 (3 self)
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Abstract. The cover time of graphs has much relevance to algorithmic applications and has been extensively investigated. Recently, with the advent of adhoc and sensor networks, an interesting class of random graphs, namely random geometric graphs, has gained new relevance and its properties have been the subject of much study. A random geometric graph G(n, r) is obtained by placing n points uniformly at random on the unit square and connecting two points iff their Euclidean distance is at most r. The phase transition behavior with respect to the radius r of such graphs has been of special interest. We show that there exists a critical radius ropt such that for any r ≥ ropt G(n, r) has optimal cover time of Θ(n log n) with high probability, and, importantly, ropt = Θ(rcon) where rcon denotes the critical radius guaranteeing asymptotic connectivity. Moreover, since a disconnected graph has infinite cover time, there is a phase transition and the corresponding threshold width is O(rcon). We are able to draw our results by giving a tight bound on the electrical resistance of G(n, r) via the power of certain constructed flows. 1
Exact analysis of latency of stateless opportunistic forwarding
 In The 28th IEEE Conference on Computer Communications (IEEE INFOCOM
, 2009
"... Abstract—Stateless opportunistic forwarding is a simple faulttolerant distributed approach for data delivery and information querying in wireless ad hoc networks, where packets are forwarded to the next available neighbors in a “random walk” fashion, until they reach the destinations or expire. This ..."
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Cited by 17 (7 self)
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Abstract—Stateless opportunistic forwarding is a simple faulttolerant distributed approach for data delivery and information querying in wireless ad hoc networks, where packets are forwarded to the next available neighbors in a “random walk” fashion, until they reach the destinations or expire. This approach is robust against ad hoc topology changes and is amenable to computation/bandwidth/energyconstrained devices; however, it is generally difficult to predict the endtoend latency suffered by such a random walk in a given network. In this paper, we make several contributions on this topic. First, by using spectral graph theory we derive a general formula for computing the exact hitting and commute times of weighted random walks on a finite graph with heterogeneous sojourn times at relaying nodes. Such sojourn times can model heterogeneous duty cycling rates in sensor networks, or heterogeneous delivery times in delay tolerant networks. Second, we study a common class of distanceregular networks with varying numbers of geographical neighbors, and obtain simple estimateformulas of hitting times by numerical analysis. Third, we study the more sophisticated settings of random geographical locations and distancedependent sojourn times through simulations. Finally, we discuss the implications of this on the optimization of latencyoverhead tradeoff. Index Terms—Opportunistic forwarding, Wireless sensor networks, Delay tolerant networks, Random walks on finite graphs,