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29
Skip Graphs
 Proc. of the 14th Annual ACMSIAM Symp. on Discrete Algorithms
, 2003
"... Skip graphs are a novel distributed data structure, based on skip lists, that provide the full functionality of a balanced tree in a distributed system where resources are stored in separate nodes that may fail at any time. They are designed for use in searching peertopeer systems, and by providin ..."
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Cited by 311 (9 self)
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Skip graphs are a novel distributed data structure, based on skip lists, that provide the full functionality of a balanced tree in a distributed system where resources are stored in separate nodes that may fail at any time. They are designed for use in searching peertopeer systems, and by providing the ability to perform queries based on key ordering, they improve on existing search tools that provide only hash table functionality. Unlike skip lists or other tree data structures, skip graphs are highly resilient, tolerating a large fraction of failed nodes without losing connectivity. In addition, constructing, inserting new nodes into, searching a skip graph, and detecting and repairing errors in the data structure introduced by node failures can be done using simple and straightforward algorithms. 1
Indexing DataOriented Overlay Networks
 In VLDB
, 2005
"... The application of structured overlay networks to implement index structures for dataoriented applications such as peertopeer databases or peertopeer information retrieval, requires highly efficient approaches for overlay construction, as changing application requirements frequently lead ..."
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Cited by 42 (13 self)
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The application of structured overlay networks to implement index structures for dataoriented applications such as peertopeer databases or peertopeer information retrieval, requires highly efficient approaches for overlay construction, as changing application requirements frequently lead to reindexing of the data and hence (re )construction of overlay networks. This problem has so far not been addressed in the literature and thus we describe an approach for the efficient construction of dataoriented, structured overlay networks from scratch in a selforganized way. Standard maintenance algorithms for overlay networks cannot accomplish this efficiently, as they are inherently sequential. Our proposed algorithm is completely decentralized, parallel, and can construct a new overlay network with short latency. At the same time it ensures good loadbalancing for skewed data key distributions which result from preserving key order relationships as necessitated by dataoriented applications. We provide both a theoretical analysis of the basic algorithms and a complete system implementation that has been tested on PlanetLab. We use this implementation to support peertopeer information retrieval and database applications.
Selfstabilizing structured ring topology p2p systems
"... We propose a selfstabilizing and modeless peertopeer(P2P) network construction and maintenance protocol, called the Ring Network(RN) protocol. The RN protocol, when started on a network of peers that are in an arbitrary state, will cause the network to converge to a structured P2P system with a di ..."
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Cited by 39 (0 self)
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We propose a selfstabilizing and modeless peertopeer(P2P) network construction and maintenance protocol, called the Ring Network(RN) protocol. The RN protocol, when started on a network of peers that are in an arbitrary state, will cause the network to converge to a structured P2P system with a directed ring topology, where peers are ordered according to their identifiers. Furthermore, the RN protocol maintains this structure in the face of peer joins and departures. The RN protocol is a distributed and asynchronous messagepassing protocol, which fits well the autonomous behavior of peers in a P2P system. The RN protocol requires only the existence of a bootstrapping system which is weakly connected. Peers do not need to be informed of any global network state, nor do they need to assist in repairing the network topology when they leave. We provide a proof of the selfstabilizing nature of the protocol, and experimentally measure the average cost (in time and number of messages) to achieve convergence. 1.
Chord on demand
 In Proceedings of the 5th International Conference on PeertoPeer Computing (P2P 2005
, 2005
"... Structured peertopeer overlay networks are now an established paradigm for implementing a wide range of distributed services. While the problem of maintaining these networks in the presence of churn and other failures is the subject of intensive research, the problem of building them from scratch ..."
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Cited by 37 (8 self)
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Structured peertopeer overlay networks are now an established paradigm for implementing a wide range of distributed services. While the problem of maintaining these networks in the presence of churn and other failures is the subject of intensive research, the problem of building them from scratch has not been addressed (apart from individual nodes joining an already functioning overlay). In this paper we address the problem of jumpstarting a popular structured overlay, Chord, from scratch. This problem is of crucial importance in scenarios where one is assigned a limited time interval in a distributed environment such as PlanetLab, or a Grid, and the overlay infrastructure needs to be set up from the ground up as quickly and efficiently as possible, or when a temporary overlay has to be generated to solve a specific task on demand. We introduce TCHORD, that can build a Chord network efficiently starting from a random unstructured overlay. After jumpstarting, the structured overlay can be handed over to the Chord protocol for further maintenance. We demonstrate through extensive simulation experiments that the proposed protocol can create a perfect Chord topology in a logarithmic number of steps. Furthermore, using a simple extension of the protocol, we can optimize the network from the point of view of message latency. 1.
Linearization: Locally selfstabilizing sorting in graphs
 University of Madrid
, 2007
"... We consider the problem of designing a distributed algorithm that, given an arbitrary connected graph G of nodes with unique labels, converts G into a sorted list of nodes. This algorithm should be as simple as possible and, for scalability, should guarantee a polylogarithmic runtime as well as at m ..."
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Cited by 18 (12 self)
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We consider the problem of designing a distributed algorithm that, given an arbitrary connected graph G of nodes with unique labels, converts G into a sorted list of nodes. This algorithm should be as simple as possible and, for scalability, should guarantee a polylogarithmic runtime as well as at most a polylogarithmic increase in the degree of each node during its execution. Furthermore, it should be selfstabilizing, that is, it should be able to eventually construct a sorted list from any state in which the graph is connected. It turns out that satisfying all of these demands at the same time is not easy. Our basic approach towards this goal is the socalled linearization technique: each node v repeatedly does the following with its neighbors: • for its left (i.e., smaller) neighbors u1,..., uk in the order of decreasing labels, v replaces {v, u1},..., {v, uk} by {v, u1}, {u1, u2},..., {uk−1, uk}, and • for its right (i.e., larger) neighbors w1,..., wℓ in the order of increasing labels, v replaces {v, w1},..., {v, wℓ} by {v, w1}, {w1, w2},..., {wℓ−1, wℓ}. As shown in this paper, this technique transforms any connected graph into a sorted list, but there are graphs for which this can take a long time. Hence, we propose several extensions of the linearization technique and experimentally evaluate their performance. Our results indicate that some of these have a polylogarithmic performance, so there is hope that there are distributed algorithms that can achieve all of our goals above. 1
A Distributed Polylogarithmic Time Algorithm for SelfStabilizing Skip Graphs
, 2009
"... Peertopeer systems rely on scalable overlay networks that enable efficient routing between its members. Hypercubic topologies facilitate such operations while each node only needs to connect to a small number of other nodes. In contrast to static communication networks, peertopeer networks allow ..."
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Cited by 15 (10 self)
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Peertopeer systems rely on scalable overlay networks that enable efficient routing between its members. Hypercubic topologies facilitate such operations while each node only needs to connect to a small number of other nodes. In contrast to static communication networks, peertopeer networks allow nodes to adapt their neighbor set over time in order to react to join and leave events and failures. This paper shows how to maintain such networks in a robust manner. Concretely, we present a distributed and selfstabilizing algorithm that constructs a (variant of the) skip graph in polylogarithmic time from any initial state in which the overlay network is still weakly connected. This is an exponential improvement compared to previously known selfstabilizing algorithms for overlay networks. In addition, individual joins and leaves are handled locally and require little work.
Clustering wavelets to speedup data dissemination in structured MANETs
"... This paper introduces a fast data dissemination method for structured peertopeer networks. The work is motivated on one side by the increase in nonvolatile memory available on mobile devices and, on the other side, by observed behavioral patterns of the users. We envision a scenario where users c ..."
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Cited by 4 (3 self)
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This paper introduces a fast data dissemination method for structured peertopeer networks. The work is motivated on one side by the increase in nonvolatile memory available on mobile devices and, on the other side, by observed behavioral patterns of the users. We envision a scenario where users come together for short periods of time (e.g. public transport, conference sessions) and wish to be able to share large collections of data. With hundreds and even thousands of data items stored on small devices, content publication is simply too energy and time consuming. By indexing summary information obtained by a combination of multiresolution analysis and kmeans, our method (HyperM) is able to cut down the overall construction time of an overlay network such as CAN by an order of magnitude, as well as provide fast approximate similarity search on such a network. The results of our extensive experimental studies confirm that HyperM is both energy and time efficient, and provides good precision and recall. 1.
Oscar: SmallWorld Overlay For Realistic Key Distributions
"... The research on P2P systems which support skewed key distributions has rapidly advanced in the recent years. Yet, the assumptions on the skews we are dealing with remained pretty simple: most of the existing literature assumes simple monotonous key distribution skews. However, this is not always t ..."
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Cited by 4 (4 self)
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The research on P2P systems which support skewed key distributions has rapidly advanced in the recent years. Yet, the assumptions on the skews we are dealing with remained pretty simple: most of the existing literature assumes simple monotonous key distribution skews. However, this is not always the case. For example, Gnutella filename traces show that complex keydistributions rather than monotonous skews occur in practice. We show that one of the seminal P2P systems which support skewed keys Mercury [7], performs poorly given such complex distributions generated from the trace of Gnutella filenames. We discuss the shortcomings of such stateoftheart techniques. We present an overlay network Oscar, based on a novel overlay construction mechanism, which does not depend on the keydistribution complexity. We demonstrate through simulations that our technique performs well and significantly surpasses Mercury for such realistic workloads.
Gossip Protocols for Renaming and Sorting
 DISC 27TH INTERNATIONAL SYMPOSIUM ON DISTRIBUTED COMPUTING
, 2013
"... We devise efficient gossipbased protocols for some fundamental distributed tasks. The protocols assume an nnode network supporting pointtopoint communication, and in every round, each node exchanges information of size O(log n) bits with (at most) one other node. We first consider the renaming ..."
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Cited by 3 (1 self)
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We devise efficient gossipbased protocols for some fundamental distributed tasks. The protocols assume an nnode network supporting pointtopoint communication, and in every round, each node exchanges information of size O(log n) bits with (at most) one other node. We first consider the renaming problem, that is, to assign distinct IDs from a small ID space to all nodes of the network. We propose a renaming protocol that divides the ID space among nodes using a natural push or pull approach, achieving logarithmic round complexity with ID space {1,..., (1 + ɛ)n}, for any fixed ɛ> 0. A variant of this protocol solves the tight renaming problem, where each node obtains a unique ID in {1,..., n}, in O(log² n) rounds. Next we study the following sorting problem. Nodes have consecutive IDs 1 up to n, and they receive numerical values as inputs. They then have to exchange those inputs so that in the end the input of rank k is located at the node with ID k. Jelasity and Kermarrec [20] suggested a simple and natural protocol, where nodes exchange values with peers chosen uniformly at random, but it is not hard to see that this protocol requires Ω(n) rounds. We prove that the same protocol works in O(log² n) rounds if peers are chosen according to a nonuniform power law distribution.
Labeling Schemes with Queries
, 2006
"... We study the question of “how robust are the known lower bounds of labeling schemes when one increases the number of consulted labels”. Let f be a function on pairs of vertices. An flabeling scheme for a family of graphs F labels the vertices of all graphs in F such that for every graph G ∈ F and e ..."
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Cited by 3 (0 self)
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We study the question of “how robust are the known lower bounds of labeling schemes when one increases the number of consulted labels”. Let f be a function on pairs of vertices. An flabeling scheme for a family of graphs F labels the vertices of all graphs in F such that for every graph G ∈ F and every two vertices u, v ∈ G, the value f(u, v) can be inferred by merely inspecting the labels of u and v. This paper introduces a natural generalization: the notion of flabeling schemes with queries, in which the value f(u, v) can be inferred by inspecting not only the labels of u and v but possibly the labels of some additional vertices. We show that inspecting the label of a single additional vertex (one query) enables us to reduce the label size of many labeling schemes significantly. In particular, we show that to support the distance function on nnode trees as well as the flow function on nnode general graphs, O(log n + log W)bit labels are sufficient and necessary, where W is the maximum (integral) capacity of an edge. We note that it was shown that any labeling scheme (without queries) supporting either the flow function on general graphs or the distance function on trees, must have label size Ω(log 2 n + log n log W). Using a single query, we also show a routing