An analytical framework for the performance evaluation of proximity-aware structured overlays

In this paper, we present an analytical study of proximity-aware structured peer-to-peer networks under churn. We use a master-equation-based approach, which is used traditionally in non-equilibrium statistical mechanics to describe steady-state or transient phenomena. In earlier work we have demonstrated that this methodology is in fact also well suited to describing structured overlay networks under churn, by showing how we can accurately predict the average number of hops taken by a lookup, for any value of churn, for the Chord system. In this paper, we extend the analysis so as to also be able to predict lookup latency, given an average latency for the links in the network. Our results show that there exists a region in the parameter space of the model, depending on churn, the number of nodes, the maintenance rates and the delays in the network, when the network cannot function as a small world graph anymore, due to the farthest connections of a node always being wrong or dead. We also demonstrate how it is possible to analyse proximity neighbour selection or proximity route selection within this formalism

A Content-Addressable Network for Similarity Search in Metric Spaces

Because of the ongoing digital data explosion, more advanced search paradigms than the traditional exact match are needed for contentbased retrieval in huge and ever growing collections of data produced in application areas such as multimedia, molecular biology, marketing, computer-aided design and purchasing assistance. As the variety of data types is fast going towards creating a database utilized by people, the computer systems must be able to model human fundamental reasoning paradigms, which are naturally based on similarity. The ability to perceive similarities is crucial for recognition, classification, and learning, and it plays an important role in scientific discovery and creativity. Recently, the mathematical notion of metric space has become a useful abstraction of similarity and many similarity search indexes have been developed. In this thesis, we accept the metric space similarity paradigm and concentrate on the scalability issues. By exploiting computer networks and applying the Peer-to-Peer communication paradigms, we build a structured network of computers able to process similarity queries in parallel. Since no centralized entities are used, such architectures are fully scalable. Specifically, we propose a Peer-to-Peer system for similarity search in metric spaces called Metric Content-Addressable Network (MCAN) which is an extension of the well known Content-Addressable Network (CAN) used for hash lookup. A prototype implementation of MCAN was tested on real-life datasets of image features, protein symbols, and text — observed results are reported. We also compared the performance of MCAN with three other, recently proposed, distributed data structures for similarity search in metric spaces

Enhancing reliability with Latin Square redundancy on desktop grids.

Computational grids are some of the largest computer systems in existence today. Unfortunately they are also, in many cases, the least reliable. This research examines the use of redundancy with permutation as a method of improving reliability in computational grid applications. Three primary avenues are explored - development of a new redundancy model, the Replication and Permutation Paradigm (RPP) for computational grids, development of grid simulation software for testing RPP against other redundancy methods and, finally, running a program on a live grid using RPP. An important part of RPP involves distributing data and tasks across the grid in Latin Square fashion. Two theorems and subsequent proofs regarding Latin Squares are developed. The theorems describe the changing position of symbols between the rows of a standard Latin Square. When a symbol is missing because a column is removed the theorems provide a basis for determining the next row and column where the missing symbol can be found. Interesting in their own right, the theorems have implications for redundancy. In terms of the redundancy model, the theorems allow one to state the maximum makespan in the face of missing computational hosts when using Latin Square redundancy. The simulator software was developed and used to compare different data and task distribution schemes on a simulated grid. The software clearly showed the advantage of running RPP, which resulted in faster completion times in the face of computational host failures. The Latin Square method also fails gracefully in that jobs complete with massive node failure while increasing makespan. Finally an Inductive Logic Program (ILP) for pharmacophore search was executed, using a Latin Square redundancy methodology, on a Condor grid in the Dahlem Lab at the University of Louisville Speed School of Engineering. All jobs completed, even in the face of large numbers of randomly generated computational host failures

Das Potential von Peer-to-Peer-Netzen und -Systemen : Architekturen, Robustheit und rechtliche Verortung

Um das Potential von P2P-Netzen und -Systemen für die Entwicklung und den Betrieb zukünftiger verteilter Systeme zu analysieren, erfolgt in der Arbeit zunächst eine umfassende Darlegung des aktuellen Entwicklungsstandes. Daraus leiten sich wesentliche Fragestellungen hinsichtlich Architektur, Robustheit und Telekommunikationsrecht ab. In der Folge werden diese untersucht, indem vorhandene Mechanismen bewertet sowie durch neuartige Verfahren ergänzt werden, um bestehende Defizite auszugleichen

Interdomain User Authentication and Privacy

This thesis looks at the issue of interdomain user authentication, i.e. user authentication in systems that extend over more than one administrative domain. It is divided into three parts. After a brief overview of related literature, the first part provides a taxonomy of current approaches to the problem. The taxonomy is first used to identify the relative strengths and weaknesses of each approach, and then employed as the basis for putting into context four concrete and novel schemes that are subsequently proposed in this part of the thesis. Three of these schemes build on existing technology; the first on 2nd and 3rd-generation cellular (mobile) telephony, the second on credit/debit smartcards, and the third on Trusted Computing. The fourth scheme is, in certain ways, different from the others. Most notably, unlike the other three schemes, it does not require the user to possess tamper-resistant hardware, and it is suitable for use from an untrusted access device. An implementation of the latter scheme (which works as a web proxy) is also described in this part of the thesis. As the need to preserve one’s privacy continues to gain importance in the digital world, it is important to enhance user authentication schemes with properties that enable users to remain anonymous (yet authenticated). In the second part of the thesis, anonymous credential systems are identified as a tool that can be used to achieve this goal. A formal model that captures relevant security and privacy notions for such systems is proposed. From this model, it is evident that there exist certain inherent limits to the privacy that such systems can offer. These are examined in more detail, and a scheme is proposed that mitigates the exposure to certain attacks that exploit these limits in order to compromise user privacy. The second part of the thesis also shows how to use an anonymous credential system in order to facilitate what we call ‘privacy-aware single sign-on’ in an open environment. The scheme enables the user to authenticate himself to service providers under separate identifier, where these identifiers cannot be linked to each other, even if all service providers collude. It is demonstrated that the anonymity enhancement scheme proposed earlier is particularly suited in this special application of anonymous credential systems. Finally, the third part of the thesis concludes with some open research questions

Security in Distributed, Grid, Mobile, and Pervasive Computing

This book addresses the increasing demand to guarantee privacy, integrity, and availability of resources in networks and distributed systems. It first reviews security issues and challenges in content distribution networks, describes key agreement protocols based on the Diffie-Hellman key exchange and key management protocols for complex distributed systems like the Internet, and discusses securing design patterns for distributed systems. The next section focuses on security in mobile computing and wireless networks. After a section on grid computing security, the book presents an overview of security solutions for pervasive healthcare systems and surveys wireless sensor network security

Netzwerke und verteilte Operation: Der Preis der Anarchie in nicht-atomarem Routing und Netzwerkformierung

The price of anarchy is a measure for performance loss due to individuals operating in a distributed manner, i.e., without or with only limited central control or without or with only limited cooperation. In the first part, a network is given and used in a distributed manner, namely for multicast routing, i.e., each sender wishes to transmit a message to multiple receivers simultaneously. We prove almost tight upper and lower bounds on the price of anarchy and conduct an experimental study. In the second part, a network is formed. Each vertex of the (to-be-built) network may invest in the building of links. The formation takes place under the knowledge that an adversary will later delete exactly one link. Vertices wish to maintain good connectivity. We prove tight upper and lower bounds on the price of anarchy for two different adversaries.Der Preis der Anarchie ist ein Maß für den Leistungsverlust dadurch, dass Individuen in verteilter Weise operieren, d.h. dass sie nicht oder nur eingeschränkt koordiniert werden oder nicht oder nur eingeschränkt kooperieren. Im ersten Teil wird ein gegebenes Netzwerk in verteilter Weise genutzt, und zwar für Multicast-Routing, d.h. es möchte jeder Sender eine Mehrzahl Empfänger gleichzeitig erreichen. Wir beweisen nahezu scharfe obere und untere Schranken für den Preis der Anarchie und führen eine experimentelle Studie durch. Im zweiten Teil geht es um die Formierung von Netzwerken. Jeder Knoten des (zu formierenden) Netzwerkes hat die Wahl, in Verbindungen zu investieren. Bei uns findet die Netzwerkformierung unter dem Wissen statt, dass später genau eine Verbindung durch einen Gegner zerstört werden wird. Die Knoten streben an, trotzdem gut verbunden zu bleiben. Wir beweisen scharfe obere und obere Schranken für den Preis der Anarchie für zwei verschiedene Formen von Gegnern

Computer science: the hardware software and heart of IT

1st edition, 201