Metaheuristic based Peer Rewiring for Semantic Overlay Networks

A Peer-to-Peer (P2P) platform is considered for collaborative Information Retrieval (IR). Each peer hosts a collection of text documents with subjects related to its owner's interests. Without a global indexing mechanism, peers locally index their documents, and provide the service to answer queries. A decentralized protocol is designed, enabling the peers to collaboratively forward queries from the initiator to the peers with relevant documents. Semantic Overlay Network (SON) is one of the state-of-the-art solutions, where peers with semantically similar resources are clustered. IR can then be efficiently performed by forwarding queries to the relevant peer clusters in an informed way. SONs are built and maintained mainly via peer rewiring. Specifically, each peer periodically sends walkers to its neighborhood. The walkers walk along peer connections, aiming at discovering more similar peers to replace less similar neighbors of its initiator. The P2P network hence gradually evolves from a random overlay network to a SON. Random and greedy walk can be applied individually or integrated in peer rewiring as a constant strategy during the progress of network evolution. However, the evolution of the network topology may affect their performance. For example, when peers are randomly connected with each other, random walk performs better than greedy walk for exploring similar peers. But as peer clusters gradually emerge in the network, a walker can explore more similar peers by following a greedy strategy. This thesis proposes an evolving walking strategy based on Simulated Annealing (SA), which evolves from a random walk to a greedy walk along the progress of network evolution. According to the simulation results, SA-based strategy outperforms current approaches, both in the efficiency to build a SON and the effectiveness of the subsequent IR. This thesis contains several advancements with respect to the state-of-the-art in this field. First of all, we identify a generic peer rewiring pattern and formalize it as a three-step procedure. Our technique provides a consistent framework for peer rewiring, while allowing enough flexibility for the users/designers to specify its properties. Secondly, we formalize SON construction as a combinatorial optimization problem, with peer rewiring as its decentralized local search solution. Based on this model, we propose a novel SA-based approach to peer rewiring. Our approach is validated via an extensive experimental study on the effect of network rewiring on (i) SON building and (ii) IR in SONs

Faster Random Walks By Rewiring Online Social Networks On-The-Fly

Many online social networks feature restrictive web interfaces which only allow the query of a user's local neighborhood through the interface. To enable analytics over such an online social network through its restrictive web interface, many recent efforts reuse the existing Markov Chain Monte Carlo methods such as random walks to sample the social network and support analytics based on the samples. The problem with such an approach, however, is the large amount of queries often required (i.e., a long "mixing time") for a random walk to reach a desired (stationary) sampling distribution. In this paper, we consider a novel problem of enabling a faster random walk over online social networks by "rewiring" the social network on-the-fly. Specifically, we develop Modified TOpology (MTO)-Sampler which, by using only information exposed by the restrictive web interface, constructs a "virtual" overlay topology of the social network while performing a random walk, and ensures that the random walk follows the modified overlay topology rather than the original one. We show that MTO-Sampler not only provably enhances the efficiency of sampling, but also achieves significant savings on query cost over real-world online social networks such as Google Plus, Epinion etc.Comment: 15 pages, 14 figure, technical report for ICDE2013 paper. Appendix has all the theorems' proofs; ICDE'201

Socially-Aware Distributed Hash Tables for Decentralized Online Social Networks

Many decentralized online social networks (DOSNs) have been proposed due to an increase in awareness related to privacy and scalability issues in centralized social networks. Such decentralized networks transfer processing and storage functionalities from the service providers towards the end users. DOSNs require individualistic implementation for services, (i.e., search, information dissemination, storage, and publish/subscribe). However, many of these services mostly perform social queries, where OSN users are interested in accessing information of their friends. In our work, we design a socially-aware distributed hash table (DHTs) for efficient implementation of DOSNs. In particular, we propose a gossip-based algorithm to place users in a DHT, while maximizing the social awareness among them. Through a set of experiments, we show that our approach reduces the lookup latency by almost 30% and improves the reliability of the communication by nearly 10% via trusted contacts.Comment: 10 pages, p2p 2015 conferenc

Strategies for cooperation emergence in distributed service discovery

This is an Accepted Manuscript of an article published by Taylor & Francis in Cybernetics and Systems on APR 3 2014], available online:http://www.tandfonline.com/10.1080/01969722.2014.894848[EN] In distributed environments where entities only have a partial view of the system, cooperation plays a key issue. In the case of decentralized service discovery in open agent societies, agents only know about the services they provide and who are their direct neighbors. Therefore, they need the cooperation of their neighbors in order to locate the required services. However, cooperation is not always present in open systems. Non-cooperative agents pursuing their own goals could refuse to forward queries from other agents to avoid the cost of this action; therefore, the efficiency of the decentralized service discovery could be seriously damaged. In this paper, we propose the ombination of incentives and local structural changes in order to promote cooperation in the service discovery process. The results show that, even in scenarios where the predominant behavior is not collaborative cooperation emerges.The work was partially supported by the Spanish Ministry of Science and Innovation through grants TIN2009-13839-C03-01, TIN2012-36586-C03-01, CSD2007-0022 (CONSOLIDER-INGENIO 2010).Del Val Noguera, E.; Rebollo Pedruelo, M.; Botti, V. (2014). Strategies for cooperation emergence in distributed service discovery. Cybernetics and Systems. 45(3):220-240. https://doi.org/10.1080/01969722.2014.894848S220240453Blanc , A. , Y.K. Liu , and A. Vahdat . “Designing Incentives for Peer-to-Peer Routing.” InProceedings of the 24th Annual Joint Conference of the IEEE Computer and Communications Societies, Vol. 1, pp. 374–385, 2005 .del Val , E. “Semantic Service Management in Service-Oriented Multi-Agent Systems.” Ph.D. thesis, Departament de Sistemes Informàtics i Computació, Universitat Politècnica de València, 2013 .Del Val, E., Rebollo, M., & Botti, V. (2012). Enhancing decentralized service discovery in open service-oriented multi-agent systems. Autonomous Agents and Multi-Agent Systems, 28(1), 1-30. doi:10.1007/s10458-012-9210-0DORAN, J. E., FRANKLIN, S., JENNINGS, N. R., & NORMAN, T. J. (1997). On cooperation in multi-agent systems. The Knowledge Engineering Review, 12(3), 309-314. doi:10.1017/s0269888997003111Eguíluz, V. M., Zimmermann, M. G., Cela‐Conde, C. J., & Miguel, M. S. (2005). Cooperation and the Emergence of Role Differentiation in the Dynamics of Social Networks. American Journal of Sociology, 110(4), 977-1008. doi:10.1086/428716Griffiths , N. and M. Luck . “Changing Neighbours: Improving Tag-Based Cooperation.” InProceedings of the 9th International Conference on Autonomous Agents and Multiagent Systems: volume 1.(AAMAS'10), 249–256. Richland, SC: International Foundation for Autonomous Agents and Multiagent Systems, 2010 .Gu , B. and S. Jarvenpaa . “Are Contributions to p2p Technical Forums Private or Public Goods? An Empirical Investigation.” Paper presented at the 1st Workshop on Economics of Peer-to-Peer Systems, June 4–5, 2004, Harvard University .Hauert, C., Traulsen, A., Brandt, H., Nowak, M. A., & Sigmund, K. (2007). Via Freedom to Coercion: The Emergence of Costly Punishment. Science, 316(5833), 1905-1907. doi:10.1126/science.1141588Hofmann , L.M. , N. Chakraborty , and K. Sycara . “The Evolution of Cooperation in Self-Interested Agent Societies: A Critical Study.” InProceedings of the 10th International Conference on Autonomous Agents and Multiagent Systems, Volume 2 , edited by K. Tumer , P. Yolum , L. Sonenberg , and P. Stone , 685–692. IFAAMAS, 2011 .Lin, W. S., Zhao, H. V., & Liu, K. J. R. (2009). Incentive Cooperation Strategies for Peer-to-Peer Live Multimedia Streaming Social Networks. IEEE Transactions on Multimedia, 11(3), 396-412. doi:10.1109/tmm.2009.2012915Nowak, M. A. (2006). Five Rules for the Evolution of Cooperation. Science, 314(5805), 1560-1563. doi:10.1126/science.1133755Nowak, M. A., & Sigmund, K. (1998). Evolution of indirect reciprocity by image scoring. Nature, 393(6685), 573-577. doi:10.1038/31225Ohtsuki, H., Hauert, C., Lieberman, E., & Nowak, M. A. (2006). A simple rule for the evolution of cooperation on graphs and social networks. Nature, 441(7092), 502-505. doi:10.1038/nature04605Santos, F. C., Santos, M. D., & Pacheco, J. M. (2008). Social diversity promotes the emergence of cooperation in public goods games. Nature, 454(7201), 213-216. doi:10.1038/nature06940Shneidman , J. and D. C. Parkes . “Rationality and Self-Interest in Peer to Peer Networks.” Paper presented at the 2nd Int. Workshop on Peer-to-Peer Systems (IPTPS’03), February 20–21, 2003, Berkeley, CA .Sigmund, K. (2007). Punish or perish? Retaliation and collaboration among humans. Trends in Ecology & Evolution, 22(11), 593-600. doi:10.1016/j.tree.2007.06.012Sigmund, K. (2009). 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DONUT: Building Shortcuts in Large-Scale Decentralized Systems with Heterogeneous Peer Distributions

Large-scale distributed systems gather thousands of peers spread all over the world. Such systems need to offer good routing performances regardless of their size and despite high churn rates. To achieve that requirement, the system must add appro- priate shortcuts to its logical graph (overlay). However, to choose efficient shortcuts, peers need to obtain information about the overlay topology. In case of heterogeneous peer distributions, retrieving such information is not straightforward. Moreover, due to churn, the topology rapidly evolves, making gathered information obsolete. State-of- the-art systems either avoid the problem by enforcing peers to adopt a uniform distri- bution or only partially fulfill these requirements. To cope with this problem, we propose DONUT, a mechanism to build a local map that approximates the peer distribution, allowing the peer to accurately estimate graph distance to other peers with a local algorithm. The evaluation performed with real latency and churn traces shows that our map increases the routing process efficiency by at least 20% compared to the state-of-the-art techniques. It points out that each map is lightweight and can be efficiently propagated through the network by consuming less than 10 bps on each peer.Les systèmes distribués à grande échelle rassemblent des milliers de noeuds répartis dans le monde. Ces systèmes doivent offrir de bonnes performances de routage indépendamment de leur taille et malgré le taux élevé de connexion\slash déconnexion. Pour cela, le système doit ajouter des raccourcis à son graphe logique (\emph{overlay} en anglais). Cependant, pour construire raccourcis efficaces, les pair ont besoin d'avoir des informations sur la topologie de l'overlay. En cas de distributions de pairs hétérogènes, la récupération de ces informations n'est pas simple. En outre, en raison du fort taux de connexion/déconnexion, la topologie évolue rapidement, ce qui rend vite les informations recueillies obsolètes. Les systèmes de l'état de l'art, soit évitent le problème en forçant les pairs à adopter une distribution uniforme, soit ne satisfont que partiellement les exigences de performances de routage. Pour faire face à ce problème, nous proposons DONUT, un mécanisme de construction d'une carte locale qui se rapproche de la distribution des pairs. Cette carte permet d'estimer localement, avec précision, la distance graphique avec les autres pairs. L'évaluation réalisée avec une matrice de latences réelles et des traces de connexion/déconnexion montre que notre carte augmente l'efficacité du routage d'au moins 20%, comparativement aux techniques de l'état de l'art. Elle montre également que chaque carte est petite et peut être propagé efficacement à travers le réseau en consommant moins de 10 bps sur chaque pair

A Secure and User Privacy-Preserving Searching Protocol for Peer-to-Peer Networks

File sharing peer-to-peer networks have become quite popular of late as a new paradigm for information exchange among large number of users in the Internet. However, these networks suffer from several problems such as fake content distribution, free riding, whitewashing, poor search scalability, lack of a robust trust model and absence of user privacy protection mechanism. In this paper, a secure and efficient searching scheme for peer-to-peer networks has been proposed that utilizes topology adaptation by constructing an overlay of trusted peers where the neighbors are selected based on their trust ratings and content similarities. While increasing the search efficiency by intelligently exploiting the formation of semantic community structures among the trustworthy peers, the scheme provides a highly reliable module for protecting the privacy of the users and data in the network. Simulation results have demonstrated that the proposed scheme provides efficient searching to good peers while penalizing the malicious peers by increasing their search times

Combination of self-organization mechanisms to enhance service discovery in open systems

Decentralized systems have emerged as an alternative to centralized approaches for dealing with dynamic requirements in new business models. These systems should provide mechanisms that contribute to flexibility and facilitate adaptation to changes in the environment. In this paper, we present two self-organization mechanisms for a decentralized service discovery system in order to improve its performance. These mechanisms are based on local actions of agents that only consider local information about queries they forward during the discovery process. The self-organization actions are chosen by each agent individually when the agent considers them to be appropriate. The actions are: remaining in the system, leaving the system, cloning, and changing structural relations with other agents. We have evaluated each self-organization mechanism separately but also the combination of the two as the environmental conditions in the service demand change. The results show that the proposed self-organization mechanisms considerably improve the performance of the service discovery systemDel Val Noguera, E.; Rebollo Pedruelo, M.; Botti Navarro, VJ. (2014). Combination of self-organization mechanisms to enhance service discovery in open systems. Information Sciences. 279:138-162. doi:10.1016/j.ins.2014.03.109S13816227