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100
Improving random walk estimation accuracy with uniform restarts
 In Algorithms and Models for the WebGraph
, 2010
"... HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte p ..."
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Cited by 36 (11 self)
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HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. appor t de r ech er ch e
Information spreading in stationary markovian evolving graphs
 In Proc. of the 23rd IEEE International Parallel and Distributed Processing Symposium (IPDPS
, 2009
"... Markovian evolving graphs [2] are dynamicgraph models where the links among a fixed set of nodes change during time according to an arbitrary Markovian rule. They are extremely general and they can well describe important dynamicnetwork scenarios. We study the speed of information spreading in the ..."
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Cited by 34 (9 self)
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Markovian evolving graphs [2] are dynamicgraph models where the links among a fixed set of nodes change during time according to an arbitrary Markovian rule. They are extremely general and they can well describe important dynamicnetwork scenarios. We study the speed of information spreading in the stationary phase by analyzing the completion time of the flooding mechanism. We prove a general theorem that establishes an upper bound on flooding time in any stationary Markovian evolving graph in terms of its nodeexpansion properties. We apply our theorem in two natural and relevant cases of such dynamic graphs: edgeMarkovian evolving graphs [24, 7] where the probability of existence of any edge at time t depends on the existence (or not) of the same edge at time t − 1; geometric Markovian evolving graphs [4, 10, 9] where the Markovian behaviour is yielded by n mobile radio stations, with fixed transmission radius, that perform n independent random walks over a square region of the plane. In both cases, the obtained upper bounds are shown to be nearly tight and, in fact, they turn out to be tight for a large range of the values of the input parameters. 1
DESENT: Decentralized and distributed semantic overlay generation in P2P networks
 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS (JSAC
, 2007
"... The current approach in web searching, i.e., centralized search engines, rises issues that question their future applicability: 1) coverage and scalability, 2) freshness, and 3) information monopoly. Performing web search using a P2P architecture that consists of the actual web servers has the pot ..."
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Cited by 27 (13 self)
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The current approach in web searching, i.e., centralized search engines, rises issues that question their future applicability: 1) coverage and scalability, 2) freshness, and 3) information monopoly. Performing web search using a P2P architecture that consists of the actual web servers has the potential to tackle those issues above. In order to achieve the desired performance and scalability, as well as enhancing search quality relative to centralized search engines, semantic overlay networks (SONs) connecting peers storing semantically related information can be employed. The lack of global content/topology knowledge in a P2P system is the key challenge in forming SONs, and this paper describes an unsupervised approach for decentralized and distributed generation of SONs (DESENT). Through simulations and analytical cost modeling we verify our claims regarding performance, scalability, and quality.
Greedy Forwarding in Dynamic ScaleFree Networks Embedded in Hyperbolic Metric Spaces
"... Abstract—We show that complex (scalefree) network topologies naturally emerge from hyperbolic metric spaces. Hyperbolic geometry facilitates maximally efficient greedy forwarding in these networks. Greedy forwarding is topologyoblivious. Nevertheless, greedy packets find their destinations with 10 ..."
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Abstract—We show that complex (scalefree) network topologies naturally emerge from hyperbolic metric spaces. Hyperbolic geometry facilitates maximally efficient greedy forwarding in these networks. Greedy forwarding is topologyoblivious. Nevertheless, greedy packets find their destinations with 100 % probability following almost optimal shortest paths. This remarkable efficiency sustains even in highly dynamic networks. Our findings suggest that forwarding information through complex networks, such as the Internet, is possible without the overhead of existing routing protocols, and may also find practical applications in overlay networks for tasks such as applicationlevel routing, information sharing, and data distribution. I.
Assisted PeertoPeer Search with Partial Indexing
, 2007
"... In the past few years, peertopeer (P2P) networks have become a promising paradigm for building a wide variety of distributed systems and applications. The most popular P2P application till today is file sharing, e.g., Gnutella, Kazza, etc. These systems are usually referred to as unstructured, an ..."
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Cited by 22 (1 self)
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In the past few years, peertopeer (P2P) networks have become a promising paradigm for building a wide variety of distributed systems and applications. The most popular P2P application till today is file sharing, e.g., Gnutella, Kazza, etc. These systems are usually referred to as unstructured, and search in unstructured P2P networks usually involves flooding or random walking. On the other hand, in structured P2P networks (DHTs), search is usually performed by looking up a distributed inverted index. The efficiency of the search mechanism is the key to the scalability of a P2P content sharing system. So far, neither unstructured nor structured P2P networks alone can solve the search problem in a satisfactory way. In this paper, we propose to combine the strengths of both unstructured and structured P2P networks to achieve more efficient search. Specifically, we propose to enhance search in unstructured P2P overlay networks by building a partial index of shared data using a structured P2P network. The index maintains two types of information: the top interests of peers and globally unpopular data, both characterized by data properties. The proposed search protocol, assisted search with partial indexing, makes use of the index to improve search in three ways: First, the index assists peers to find other peers with similar interests and the unstructured search overlay is formed to reflect peer interests. Second, the index also provides search hints for those data difficult to locate by exploring peer interest locality, and these hints can be used for secondchance search. Third, the index helps to locate unpopular data items. Experiments based on a P2P file sharing trace show that the assisted search with a lightweight partial indexing service can significantly improve the success rate in locating data than Gnutella and a hitratebased protocol in unstructured P2P systems, while incurring low search latency and overheads.
Exploiting Dynamic Querying like Flooding Techniques in Unstructured PeerToPeer Networks
, 2005
"... In unstructured peertopeer networks, controlled flooding aims at locating an item at the minimum message cost. Dynamic querying is a new controlled flooding technique. While it is implemented in some peertopeer networks, little is known about its undesirable behavior and little is known about it ..."
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Cited by 21 (4 self)
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In unstructured peertopeer networks, controlled flooding aims at locating an item at the minimum message cost. Dynamic querying is a new controlled flooding technique. While it is implemented in some peertopeer networks, little is known about its undesirable behavior and little is known about its general usefulness in unstructured peerto peer networks. This paper describes the first evaluation and analysis of such techniques, and proposes novel techniques to improve them. We make three contributions. First, we find the current dynamic querying design is flawed. Although it is advantageous over the expanding ring algorithm in terms of search cost, it is much less attractive in terms of peer perceived latency, and its strict constraints on network connectivity prevent it from being widely adopted. Second, we propose an enhanced flooding technique which requires the search cost close to the minimum, reduces the search latency by more than four times, and loosens the constraints on the network connectivity. Thus, we make such techniques useful for the general unstructured peertopeer networks. Third, we show that our proposal requires only minor modifications to the existing search mechanisms and can be incrementally deployed in peertopeer networks.
Fast distributed random walks
 In PODC
, 2009
"... Performing random walks in networks is a fundamental primitive that has found applications in many areas of computer science, including distributed computing. In this paper, we focus on the problem of performing random walks efficiently in a distributed network. Given bandwidth constraints, the goal ..."
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Performing random walks in networks is a fundamental primitive that has found applications in many areas of computer science, including distributed computing. In this paper, we focus on the problem of performing random walks efficiently in a distributed network. Given bandwidth constraints, the goal is to minimize the number of rounds required to obtain a random walk sample. All previous algorithms that compute a random walk sample of length ℓ as a subroutine always do so naively, i.e., in O(ℓ) rounds. The main contribution of this paper is a fast distributed algorithm for performing random walks. We show that a random walk sample of length ℓ can be computed in Õ(ℓ2/3D 1/3) rounds on an undirected unweighted network, where D is the diameter of the network. 1 When ℓ = Ω(D log n), this is an improvement over the naive O(ℓ) bound. (We show that Ω(min{D, ℓ}) is a lower bound and hence in general we cannot have a running time faster than the diameter of the graph.) We also show that our algorithm can be applied to speedup the more general MetropolisHastings sampling. We extend our algorithms to perform a large number, k, of random walks efficiently. We show how k destinations can be sampled in Õ((kℓ)2/3 D 1/3) rounds if k ≤ ℓ 2 and Õ((kℓ)1/2) rounds otherwise. We also present faster algorithms for performing random walks of length larger than (or equal to) the mixing time of the underlying graph. Our techniques can be useful in speeding up distributed algorithms for a variety of applications that use random walks as a subroutine.
Performance Analysis of Probabilistic Flooding Using Random Graphs
"... Probabilistic flooding (parameterized by a forwarding probability) has frequently been considered in the past, as a means of limiting the large message overhead associated with traditional (full) flooding approaches that are used to disseminate globally information in unstructured peertopeer and ot ..."
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Cited by 14 (7 self)
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Probabilistic flooding (parameterized by a forwarding probability) has frequently been considered in the past, as a means of limiting the large message overhead associated with traditional (full) flooding approaches that are used to disseminate globally information in unstructured peertopeer and other networks. A key challenge in using probabilistic flooding is the determination of the forwarding probability so that global network outreach is achieved while keeping the message overhead as low as possible. By showing that a probabilistic flooding network generated by applying probabilistic flooding to a connected random graph network can be bounded by properly parameterized random graph networks and invoking random graph theory results, bounds on the value of the forwarding probability are derived guaranteeing global network outreach with high probability, while significantly reducing the message overhead. Bounds on the average number of messages – as well as asymptotic expressions and on the average time required to complete network outreach are also derived, illustrating the benefits of the properly parameterized probabilistic flooding scheme. 1.
Limited ScaleFree Overlay Topologies for Unstructured PeertoPeer Networks
 also in IEEE ICDCS 2007
, 2009
"... Abstract—In unstructured peertopeer (P2P) networks, the overlay topology (or connectivity graph) among peers is a crucial component in addition to the peer/data organization and search. Topological characteristics have profound impact on the efficiency of a search on such unstructured P2P networks ..."
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Cited by 10 (2 self)
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Abstract—In unstructured peertopeer (P2P) networks, the overlay topology (or connectivity graph) among peers is a crucial component in addition to the peer/data organization and search. Topological characteristics have profound impact on the efficiency of a search on such unstructured P2P networks, as well as other networks. A key limitation of scalefree (powerlaw) topologies is the high load (i.e., high degree) on a very few number of hub nodes. In a typical unstructured P2P network, peers are not willing to maintain high degrees/loads as they may not want to store a large number of entries for construction of the overlay topology. Therefore, to achieve fairness and practicality among all peers, hard cutoffs on the number of entries are imposed by the individual peers, which limits scalefreeness of the overall topology, hence limited scalefree networks. Thus, it is expected that the efficiency of the flooding search reduces as the size of the hard cutoff does. We investigate the construction of scalefree topologies with hard cutoffs (i.e., there are not any major hubs) and the effect of these hard cutoffs on the search efficiency. Interestingly, we observe that the efficiency of normalized flooding and random walk search algorithms increases as the hard cutoff decreases. Index Terms—Unstructured peertopeer networks, scalefree networks, powerlaw networks, search efficiency, cutoff. Ç 1