Performance study of unstructured peer-to-peer systems

Peer-to-peer (P2P) applications became widely known in 1999 with its first popular representative, the audio file sharing system Napster. Napster was one of the most competitive P2P systems, even if it was characterized as a “centralized P2P” system, because the file exchanging was transparently distributed but the file indexing was strictly centralized. Following Napster, a significant number of “fully decentralized P2P” file sharing applications (e.g. Kazaa and Freenet) were developed and research interest in P2P concepts grew, not only for file sharing purposes but also for uses like distribution of computing power and storage, handling of complex processing jobs and instant messaging. In this thesis, the performance of the content search process of peer-to-peer systems is studied aiming to identify the main factors that vary the search time and the search results. Previously proposed algorithms for performance improvement based on overlay topology adaptation are studied in detail. Based on the outcome of these studies, some modifications to the topology adaptation algorithms are proposed, as well as a new adaptive algorithm that combines certain advantages of the proposed algorithms in order to further improve the performance of unstructured peer-to-peer networks.Οι εφαρμογές των δικτύων ομότιμων οντοτήτων (peer-to-peer) έγιναν ευρέως γνωστές το 1999 με το πρώτο δημοφιλές αντιπρόσωπό τους, το σύστημα διαμοιρασμού μουσικών αρχείων Napster. Το Napster ήταν ένα από τα πιο ανταγωνιστικά συστήματα ομότιμων οντοτήτων, παρότι έχει χαρακτηριστεί από πολλούς ως «κεντροποιημένο» σύστημα, εξαιτίας του γεγονότος ότι η ανταλλαγή αρχείων ήταν διαφανώς κατανεμημένη ενώ το ευρετήριο των αρχείων (file indexing) ήταν αποθηκευμένο σε έναν κεντρικό εξυπηρετητή. Μετά το Napster αναπτύχθηκε ένας αρκετά μεγάλος αριθμός από πλήρως αποκεντρωμένες εφαρμογές ομότιμων οντοτήτων (όπως το Kazaa και το Freenet) και το ερευνητικό ενδιαφέρον για τα δίκτυα ομότιμων οντοτήτων αυξήθηκε, όχι μόνο για εφαρμογές διαμοιρασμού αρχείων αλλά και για χρήσεις όπως είναι η κατανεμημένη επεξεργασία, η κατανεμημένη αποθήκευση, ο χειρισμός πολύπλοκων επεξεργαστικών εργασιών και η απευθείας ανταλλαγή μηνυμάτων (instant messaging). Στην παρούσα διατριβή μελετάται, σε πρώτο στάδιο, η επίδοση της διαδικασίας αναζήτησης περιεχομένου στα δίκτυα ομότιμων οντοτήτων. Ο σκοπός της μελέτης αυτής είναι η εύρεση των παραγόντων που επηρεάζουν τόσο τον χρόνο όσο και τα αποτελέσματα της αναζήτησης. Στη συνέχεια, συγκρίνονται οι σημαντικότεροι προσαρμοστικοί αλγόριθμοι της τοπολογίας των ομότιμων οντοτήτων ως προς την επίδοσή τους κατά τη διαδικασία της αναζήτησης, με τη χρήση προσομοιώσεων. Βάσει των συμπερασμάτων της μελέτης αυτής προτείνονται βελτιώσεις στους τρέχοντες προσαρμοστικούς αλγόριθμους, καθώς και ένας νέος προσαρμοστικός αλγόριθμος που συνδυάζει πλεονεκτήματα των αλγορίθμων αυτών, με σκοπό την περαιτέρω βελτίωση της επίδοσης των μη δομημένων (unstructured) δικτύων ομότιμων οντοτήτων

Leveraging Ontologies upon a Holistic Privacy-Aware Access Control Model

International audienceAccess control is a crucial concept in both ICT security and privacy, providing for the protection of system resources and personal data. The increasing complexity of nowadays systems has led to a vast family of solutions fostering comprehensive access control models, with the ability to capture a variety of parameters and to incorporate them in the decision making process. However, existing approaches are characterised by limitations regarding expressiveness. We present an approach that aims at overcoming such limitations. It is fully based on ontologies and grounded on a rich in semantics information model. The result is a privacy-aware solution that takes into consideration a variety of aspects and parameters, including attributes, context, dependencies between actions and entities participating therein, as well as separation and binding of duty constraints

Facilitating GDPR Compliance: The H2020 BPR4GDPR Approach

Part 2: Trust and Privacy Aspects of Smart Information Environments - TPSIEInternational audienceThis paper outlines the approach followed by the H2020 BPR4GDPR project to facilitate GDPR compliance. Its goal is to provide a holistic framework able to support end-to-end GDPR-compliant intra- and inter-organisational ICT-enabled processes at various scales, while also being generic enough, fulfilling operational requirements covering diverse application domains. To this end, solutions proposed by BPR4GDPR cover the full process lifecycle addressing major challenges and priorities posed by the Regulation

Privacy Regulations, Context aware services,

middleware Recent advances in mobile communications, location/sensing technologies and data processing are boosting the deployment of context-aware services and smart spaces creation. This is reflected in urban environments by the smart-city vision, a city with advanced ICT and surveillance infrastructures offering to citizens a diversity of services. Nevertheless, privacy risks and threats ambush, since collection and process of large amount of personal data occur. Although technology enables the collection of data, its protection against abuse is left to data protection legislation. However, privacy terms to be regarded as legislature issues, should be brought down in the technological reality and carefully accounted for in devising technical solutions. In order to limit the disclosure and misuse of citizens ’ personal data, this report introduces a distributed unit o

Facilitating GDPR compliance: the H2020 BPR4GDPR approach

This paper outlines the approach followed by the H2020 BPR4GDPR project to facilitate GDPR compliance. Its goal is to provide a holistic framework able to support end-to-end GDPR-compliant intra- and inter-organisational ICT-enabled processes at various scales, while also being generic enough, fulfilling operational requirements covering diverse application domains. To this end, solutions proposed by BPR4GDPR cover the full process lifecycle addressing major challenges and priorities posed by the Regulation