Revisiting Content Availability in Distributed Online Social Networks

Online Social Networks (OSN) are among the most popular applications in today's Internet. Decentralized online social networks (DOSNs), a special class of OSNs, promise better privacy and autonomy than traditional centralized OSNs. However, ensuring availability of content when the content owner is not online remains a major challenge. In this paper, we rely on the structure of the social graphs underlying DOSN for replication. In particular, we propose that friends, who are anyhow interested in the content, are used to replicate the users content. We study the availability of such natural replication schemes via both theoretical analysis as well as simulations based on data from OSN users. We find that the availability of the content increases drastically when compared to the online time of the user, e. g., by a factor of more than 2 for 90% of the users. Thus, with these simple schemes we provide a baseline for any more complicated content replication scheme.Comment: 11pages, 12 figures; Technical report at TU Berlin, Department of Electrical Engineering and Computer Science (ISSN 1436-9915

PFS: A Productivity Forecasting System For Desktop Computers To Improve Grid Applications Performance In Enterprise Desktop Grid

An Enterprise Desktop Grid (EDG) is a low cost platform that gathers desktop computers spread over different institutions. This platform uses desktop computers idle time to run Grid applications. We argue that computers in these environments have a predictable productivity that affects a Grid application execution time. In this paper, we propose a system called PFS for computer productivity forecasting that improves Grid applications performance. We simulated 157.500 applications and compared the performance achieved by our proposal against two recent strategies. Our experiments show that a Grid scheduler based on PFS runs applications faster than schedulers based on other selection strategies.Fil: Salinas, Sergio Ariel. Universidad Nacional de Cuyo; ArgentinaFil: Garcia Garino, Carlos Gabriel. Universidad Nacional de Cuyo; ArgentinaFil: Zunino Suarez, Alejandro Octavio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil. Instituto Superior de Ingenieria del Software; Argentin

PFS: A Productivity Forecasting System for Desktop Computers to Improve Grid Applications Performance in Enterprise Desktop Grid

An Enterprise Desktop Grid (EDG) is a low cost platform that gathers desktop computers spread over different institutions. This platform uses desktop computers idle time to run Grid applications. We argue that computers in these environments have a predictable productivity that affects a Grid application execution time. In this paper, we propose a system called PFS for computer productivity forecasting that improves Grid applications performance. We simulated 157.500 applications and compared the performance achieved by our proposal against two recent strategies. Our experiments show that a Grid scheduler based on PFS runs applications faster than schedulers based on other selection strategies

Multi-Path Link Embedding for Survivability in Virtual Networks

Internet applications are deployed on the same network infrastructure, yet they have diverse performance and functional requirements. The Internet was not originally designed to support the diversity of current applications. Network Virtualization enables heterogeneous applications and network architectures to coexist without interference on the same infrastructure. Embedding a Virtual Network (VN) into a physical network is a fundamental problem in Network Virtualization. A VN Embedding that aims to survive physical (e.g., link) failures is known as the Survivable Virtual Network Embedding (SVNE). A key challenge in the SVNE problem is to ensure VN survivability with minimal resource redundancy. To address this challenge, we propose SiMPLE. By exploiting path diversity in the physical network, SiMPLE provides guaranteed VN survivability against single link failure while incurring minimal resource redundancy. In case of multiple arbitrary link failures, SiMPLE provides maximal survivability to the VNs. We formulate this problem as an ILP and implement it using GNU Linear Programming Kit (GLPK). We propose a greedy proactive to solve larger instances of the problem in case of single link failures. In presence of more than one link failures, we propose a greedy reactive algorithm as an extension to the previous one, which opportunistically recovers the lost bandwidth in the VNs. Simulation results show that SiMPLE outperforms full backup and shared backup schemes for SVNE, and produces near-optimal results

Privacy in DOSN: un approccio basato su controllo degli accessi

La Tesi tratta lo sviluppo di un sistema distribuito per il social networking, dove il controllo degli accessi e la persistenza dei dati vengono gestiti tramite un framework di Access Control XACML. La valutazione delle performance è effettuata attraverso una simulazione con dataset reali

Privacy in DOSN: un approccio basato su controllo degli accessi

La Tesi tratta lo sviluppo di un sistema distribuito per il social networking, dove il controllo degli accessi e la persistenza dei dati vengono gestiti tramite un framework di Access Control XACML. La valutazione delle performance è effettuata attraverso una simulazione con dataset reali

Availability-based persistence in reti sociali P2P

Le Distributed Online Social Networks (DOSNs) sono una sottoclasse delle OSNs che garantiscono un alto livello di autonomia e privacy. Questa tesi propone un approccio dinamico e totalmente distribuito al problema della persistenza dei dati nelle DOSNs che, basandosi sulla availability dei peer e sul concetto di trust tra utenti, garantisce un alto grado di disponibilità dei dati all’interno della rete. La persistenza dei dati nel sistema viene garantita attraverso l’elezione di un insieme di punti di memorizzazione, detti social cache, per i dati degli utenti. Le social cache, scelte in base alla loro centralità nella rete e alla loro disponibilità nel sistema, memorizzano o sono in grado di accedere ai dati dei propri amici offline, rendendoli disponibili a tutti i propri vicini che hanno diritto ad accedervi. È stata inoltre realizzata un’implementazione del nostro modello in PeerSim, un simulatore scalabile per reti P2P. I risultati raccolti con le nostre simulazioni testimoniano la bontà dell’approccio proposto. Distributed Online Social Networks (DOSNs) are a subset of OSNs that ensure a high level of autonomy and privacy. This thesis proposes a dynamic and fully distributed approach to the problem of data persistence in DOSNs. Our model is based on node availability and on trust between users and ensures a high level of data availability in the network. Data persistence in the system is achieved through the election of a set of points of storage, called social caches, for users’ data. Social caches, which are chosen according to their centrality and their availability in the system, store or are able to access to their offline friends’ data, making them available to all their neighbours who have the right to access them. We also show an implementation of our model in PeerSim, a scalable P2P simulator. The results obtained with our simulations show the validity of our approach