Sia Ka Cheung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 85-91). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Problem Statement --- p.1 / Chapter 1.2 --- Contributions --- p.3 / Chapter 1.3 --- Thesis Organization --- p.4 / Chapter 2 --- Background --- p.5 / Chapter 2.1 --- Content-Based Image Retrieval --- p.5 / Chapter 2.1.1 --- Feature Extraction --- p.6 / Chapter 2.1.2 --- Indexing and Retrieval --- p.7 / Chapter 2.2 --- Relevance Feedback --- p.7 / Chapter 2.2.1 --- Weight Updating --- p.9 / Chapter 2.2.2 --- Bayesian Formulation --- p.11 / Chapter 2.2.3 --- Statistical Approaches --- p.12 / Chapter 2.2.4 --- Inter-query Feedback --- p.12 / Chapter 2.3 --- Peer-to-Peer Information Retrieval --- p.14 / Chapter 2.3.1 --- Distributed Hash Table Techniques --- p.16 / Chapter 2.3.2 --- Routing Indices and Shortcuts --- p.17 / Chapter 2.3.3 --- Content-Based Retrieval in P2P Systems --- p.18 / Chapter 3 --- Parameter Estimation-Based Relevance Feedback --- p.21 / Chapter 3.1 --- Parameter Estimation of Target Distribution --- p.21 / Chapter 3.1.1 --- Motivation --- p.21 / Chapter 3.1.2 --- Model --- p.23 / Chapter 3.1.3 --- Relevance Feedback --- p.24 / Chapter 3.1.4 --- Maximum Entropy Display --- p.26 / Chapter 3.2 --- Self-Organizing Map Based Inter-Query Feedback --- p.27 / Chapter 3.2.1 --- Motivation --- p.27 / Chapter 3.2.2 --- Initialization and Replication of SOM --- p.29 / Chapter 3.2.3 --- SOM Training for Inter-query Feedback --- p.31 / Chapter 3.2.4 --- Target Estimation and Display Set Selection for Intra- query Feedback --- p.33 / Chapter 3.3 --- Experiment --- p.35 / Chapter 3.3.1 --- Study of Parameter Estimation Method Using Synthetic Data --- p.35 / Chapter 3.3.2 --- Performance Study in Intra- and Inter- Query Feedback . --- p.40 / Chapter 3.4 --- Conclusion --- p.42 / Chapter 4 --- Distributed COntent-based Visual Information Retrieval --- p.44 / Chapter 4.1 --- Introduction --- p.44 / Chapter 4.2 --- Peer Clustering --- p.45 / Chapter 4.2.1 --- Basic Version --- p.45 / Chapter 4.2.2 --- Single Cluster Version --- p.47 / Chapter 4.2.3 --- Multiple Clusters Version --- p.51 / Chapter 4.3 --- Firework Query Model --- p.53 / Chapter 4.4 --- Implementation and System Architecture --- p.57 / Chapter 4.4.1 --- Gnutella Message Modification --- p.57 / Chapter 4.4.2 --- Architecture of DISCOVIR --- p.59 / Chapter 4.4.3 --- Flow of Operations --- p.60 / Chapter 4.5 --- Experiments --- p.62 / Chapter 4.5.1 --- Simulation Model of the Peer-to-Peer Network --- p.62 / Chapter 4.5.2 --- Number of Peers --- p.66 / Chapter 4.5.3 --- TTL of Query Message --- p.70 / Chapter 4.5.4 --- Effects of Data Resolution on Query Efficiency --- p.73 / Chapter 4.5.5 --- Discussion --- p.74 / Chapter 4.6 --- Conclusion --- p.77 / Chapter 5 --- Future Works and Conclusion --- p.79 / Chapter A --- Derivation of Update Equation --- p.81 / Chapter B --- An Efficient Discovery of Signatures --- p.82 / Bibliography --- p.85

Wang, Yongzhi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (p.68-72). / Abstract also in Chinese. / Abstract --- p.i / Acknowledgement --- p.ii / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Abstract Model --- p.7 / Chapter 2.1 --- Request allocation problem --- p.7 / Chapter 2.2 --- Neighbor selection problem --- p.11 / Chapter 3 --- Simulation Model --- p.14 / Chapter 4 --- Load Balancing Algorithms --- p.18 / Chapter 4.1 --- Request allocation --- p.18 / Chapter 4.2 --- Neighbor selection algorithms --- p.24 / Chapter 4.2.1 --- What to measure? --- p.24 / Chapter 4.2.2 --- Timeout-based neighbor selection algorithms --- p.25 / Chapter 4.2.3 --- Periodic neighbor selection algorithms --- p.33 / Chapter 4.2.4 --- Comparison: Timeout-based versus Periodical neighbor selection algorithms --- p.39 / Chapter 4.3 --- Further experiments --- p.41 / Chapter 4.3.1 --- Request window size --- p.41 / Chapter 4.3.2 --- Impact of K --- p.42 / Chapter 4.3.3 --- Adaptive adjustment of the neighbor selection period --- p.43 / Chapter 4.3.4 --- Performance with adequate bandwidth --- p.45 / Chapter 5 --- Minimizing Server´ةs Load --- p.49 / Chapter 6 --- Background Study --- p.56 / Chapter 6.1 --- P2P content distribution system --- p.56 / Chapter 6.1.1 --- P2P File sharing system --- p.56 / Chapter 6.1.2 --- P2P streaming system --- p.59 / Chapter 6.1.3 --- P2P Video on Demand system --- p.61 / Chapter 6.2 --- Congestion control --- p.62 / Chapter 7 --- Conclusion --- p.67 / Bibliography --- p.68

Lin, Minghong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 49-51). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.v / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- A Stochastic Framework --- p.5 / Chapter 2.1 --- Model Description --- p.5 / Chapter 2.2 --- Altruistic File Sharing System with Download Con- straint --- p.7 / Chapter 2.2.1 --- Model Formulation --- p.8 / Chapter 2.2.2 --- Steady State Analysis --- p.9 / Chapter 2.3 --- Altruistic File Sharing System with Download and Upload Constraints --- p.14 / Chapter 2.3.1 --- Model Formulation --- p.14 / Chapter 2.3.2 --- Steady State Analysis --- p.15 / Chapter 2.4 --- Incentive File Sharing via Coordinated Matching --- p.18 / Chapter 2.4.1 --- Without Incentive Mechanism --- p.18 / Chapter 2.4.2 --- With Incentive Mechanism --- p.19 / Chapter 2.5 --- Simulation --- p.23 / Chapter 3 --- An ISP-friendly Protocol --- p.28 / Chapter 3.1 --- Simple Mathematical Models --- p.28 / Chapter 3.1.1 --- Assumptions --- p.29 / Chapter 3.1.2 --- Homogeneous Case Analysis --- p.30 / Chapter 3.1.3 --- Heterogeneous Case Analysis --- p.31 / Chapter 3.1.4 --- Flash Crowd Analysis --- p.32 / Chapter 3.2 --- An ISP-friendly BitTorrent Protocol --- p.33 / Chapter 3.3 --- Performance Evaluation & Measurements --- p.36 / Chapter 3.3.1 --- Choice of the BitTorrent Client --- p.37 / Chapter 3.3.2 --- Experimental Setup --- p.37 / Chapter 3.3.3 --- Regular Peer Arrival --- p.38 / Chapter 3.3.4 --- Flash Crowd --- p.41 / Chapter 3.4 --- Black Hole Security Attack --- p.42 / Chapter 4 --- Related Work --- p.46 / Chapter 5 --- Conclusion --- p.48 / Bibliography --- p.49 / Appendix --- p.52

Lu, Mengwei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (p. 52-54). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Introduction of P2P-VoD Systems --- p.5 / Chapter 2.1 --- Major Components of the System --- p.5 / Chapter 2.2 --- Peer Join and Content Discovery --- p.6 / Chapter 2.3 --- Segment Sizes and Replication Strategy --- p.7 / Chapter 2.4 --- Piece Selection --- p.8 / Chapter 2.5 --- Transmission Strategy --- p.9 / Chapter 3 --- Detection Methodology --- p.10 / Chapter 3.1 --- Capturing Technique --- p.11 / Chapter 3.2 --- Analytical Framework --- p.15 / Chapter 3.3 --- Results of our Detection Methodology --- p.24 / Chapter 4 --- Protective Architecture --- p.25 / Chapter 4.1 --- Architecture Overview --- p.25 / Chapter 4.2 --- Content Servers --- p.27 / Chapter 4.3 --- Shield Nodes --- p.28 / Chapter 4.4 --- Tracker --- p.29 / Chapter 4.5 --- A Randomized Assignment Algorithm --- p.30 / Chapter 4.6 --- Seeding Algorithm --- p.31 / Chapter 4.7 --- Connection Management Algorithm --- p.33 / Chapter 4.8 --- Advantages of the Shield Nodes Architecture --- p.33 / Chapter 4.9 --- Markov Model for Shield Nodes Architecture Against Single Track Anonymity Attack --- p.35 / Chapter 5 --- Experiment Result --- p.40 / Chapter 5.1 --- Shield Node architecture against anonymity attack --- p.40 / Chapter 5.1.1 --- Performance Analysis for Single Track Anonymity Attack --- p.41 / Chapter 5.1.2 --- Experiment Result on PlanetLab for Single Track Anonymity Attack --- p.42 / Chapter 5.1.3 --- Parallel Anonymity Attack --- p.44 / Chapter 5.2 --- Shield Nodes architecture-against DoS attack --- p.45 / Chapter 6 --- Related Work --- p.48 / Chapter 7 --- Future Work --- p.49 / Chapter 8 --- Conclusion --- p.50

Abstract not available

One of the activities of most successful intruders of a computer system is to modify data on the victim,either to hide his/her presence and to destroy the evidence of the break-in, or to subvert the system completely and make it accessible for further abuse without triggering alarms.File integrity checking is one common method to mitigate the effects of successful intrusions by detecting the changes an intruder makes to files on a computer system. Historically file integrity checking has been implemented using tools that operate locally on a single system, which imposes quite some restrictions regardingmaintenance and scalability. Recent improvements for large scale environments have introduced trusted central servers which provide secure fingerprint storage and logging facilities, but such centralism presents some new shortcomings.This thesis describes an alternative, decentralised approach where peer-to-peer mechanisms are used to provide fingerprint storage for file integrity checking with more flexibility and scalability than offered by currently available systems. A research implementation has been developed to verify the approach as viable and practical, and experimental results obtained with that prototype are discussed.

With the extremely rapid development of the Internet in recent years, emerging peer-to-peer network overlays are meeting the requirements of a more sophisticated communications environment, providing a useful substrate for applications such as scalable file sharing, data storage, large-scale multicast, web-cache, and publish-subscribe services. Due to its design flexibility, peer-to-peer networks can offer features including self-organization, fault-tolerance, scalability, load-balancing, locality and anonymity. As the Internet grows, there is an urgent requirement to understand real-time network performance degradation. Measurement tools currently used are ping, traceroute and variations of these. SNMP (Simple Network Management Protocol) is also used by network administrators to monitor local networks. However, ping and traceroute can only be used temporarily, SNMP can only be deployed at certain points in networks and these tools are incapable of sharing network measurements among end-users. Due to the distributed nature of networking performance data, peer-to-peer overlay networks present an attractive platform to distribute this information among Internet users. This thesis aims at investigating the desirable locality property of peer-to-peer overlays to create an application to share Internet measurement performance. When measurement data are distributed amongst users, it needs to be localized in the network allowing users to retrieve it when external Internet links fail. Thus, network locality and robustness are the most desirable properties. Although some unstructured overlays also integrate locality in design, they fail to reach rarely located data items. Consequently, structured overlays are chosen because they can locate a rare data item deterministically and they can perform well during network failures. In structured peer-to-peer overlays, Tapestry, Pastry and Chord with proximity neighbour selection, were studied due to their explicit notion of locality. To differentiate the level of locality and resiliency in these protocols, P2Psim simulations were performed. The results show that Tapestry is the more suitable peer-to-peer substrate to build such an application due to its superior localizing data performance. Furthermore, due to the routing similarity between Tapestry and Pastry, an implementation that shares network measurement information was developed on freepastry, verifying the application feasibility. This project also contributes to the extension of P2Psim to integrate with GT-ITM and link failures.

University of Technology, Sydney. Faculty of Information Technology. / Over the last few years Peer-to-Peer (P2P) systems have emerged as highly attractive systems supporting many useful large-scale applications and services. They allow the exploitation of enormous untapped resources (such as idle processing cycles, storage, and bandwidth) available at Internet-connected devices, which were previously considered incapable of providing services to others. Participating nodes (peers) form an overlay network and communicate with each other without being controlled by a central authority. The structures and routing decisions of the most current P2P networks often do not correlate with the Internet infrastructure. In doing so, the tasks of overlay construction and routing become less complicated however, this results in high end-to-end delay for the P2P applications. As a consequence, the P2P networks may not be able to provide stringent Quality of Service (QoS) requirements for a new generation of P2P applications, and thus limit their benefits for the end users. Moreover, the infrastructure ignorance means P2P systems waste Internet resources by adding more than they should to the Internet traffic. This leads to the increase in Internet access costs substantially, and in turn the P2P systems do not scale well. The thesis presents a novel architecture for developing efficient P2P systems, and new schemes for constructing infrastructure-aware overlay networks. The main objective is first, to overcome the disparity between the overlay and Internet structures in order to maximize the use of network resources and reduce the overlay delay to the P2P applications; second, to provide efficient communication for P2P systems enabling deployment of any P2P applications while preserving decentralized, self-organizing and self-maintaining characteristics for the systems. To achieve these goals, we firstly developed Geographically Longest Prefix Matching (Geo-LPM) and Geographical Partitioning (Geo-Partitioning) schemes to cluster nodes that are close to each other in terms of network latency and network membership, and to determine links between neighboring clusters respectively. The developed schemes are efficient, generate low overhead, and help to produce excellent physically/infrastructure-aware overlay networks. Their distinctive features are self-organization, self-maintenance, and decentralization, which make them suitable to work in a P2P environment. Secondly we propose a novel architecture, called a physically-aware reference model (PARM) that captures desirable features for P2P systems by resolving major functional P2P system problems efficiently in a layered structure. For example, the application routing layer of PARM deals with routing inefficiency, meanwhile the infrastructure unawareness is resolved at the overlay network layer. We develop a useful P2P application, called a Peer Name Service (PNS) that interprets node names into their current IP addresses for any Internet-connected devices. Using the overlay networks, the PNS can support devices, which could be unreachable via the Domain Name Server (DNS), and mobile devices on-the-move without prior setup requirement in a distributed and timely fashion. Finally, to validate the whole concept of PARM, we simulate the PNS and a file transfer to a mobile node at the top layer of PARM, the P2P application layer. Since the PNS is sensitive to delay, it would be useful to evaluate the impacts of overlay delay factor and PARM on the performance of P2P applications. The simulation results show that the performance of the PARM-based applications is significantly improved while achieving decentralized and self-organizing features. The results also indicate that PARM can be a recommended reference model for developing scalable and efficient P2P systems.

This thesis investigates an innovative framework and process coordination technologies for peer-to-peer based decentralised workflow systems. The aim of this work is to address some of the unsolved problems in the contemporary workflow research rudimentally from an architectural viewpoint. The problems addressed in this thesis, i.e., bad performance, vulnerability to failures, poor scalability, user restrictions, unsatisfactory system openness, and lack of support for incompletely specified processes, have become major obstacles for wide deployment of workflow in real-world. After an in-depth analysis of the above problems, this thesis reveals that most of these problems are mainly caused by the mismatch between application nature, i.e., distributed, and system design, i.e., centralised management. Thus, the old-fashioned client-server paradigm which is conventionally used in most of today�s workflow systems should be replaced with a peer-to-peer based, open,collaborative and decentralised framework which can reflect workflow�s distributed feature more naturally. Combining workflow technology and peer-to-peer computing technology, SwinDeW which is a genuinely decentralised workflow approach is proposed in this thesis. The distinguished design of SwinDeW removes both the centralised data repository and the centralised workflow engine from the system. Hence, workflow participants are facilitated by automated peers which are able to communicate and collaborate with one another directly to fulfil both build-time and run-time workflow functions. To achieve this goal, an innovative data storage approach, known as �know what you should know�, is proposed, which divides a process model into individual task partitions and distributes each partition to relevant peers properly according to the capability match. Based on such a data storage approach, the novel mechanisms for decentralised process instantiation, instance execution and execution monitoring are explored. Moreover, SwinDeW is further extended to support incompletely-specified processes in the decentralised environment. New technologies for handling incompletely-specified processes at run-time are presented. The major contributions of this research are an innovative, decentralised workflow system framework and corresponding process coordination technologies for system functionality. Issues regarding system performance, reliability, scalability,user support, system openness, and incompletely-specified process support are discussed deeply. Moreover, this thesis also contributes the SwinDeW prototype which implements and demonstrates this design and functionality for proof-of concept purposes. With these outcomes, performance bottlenecks in workflow systems are likely to be eliminated whilst increased resilience to failure, enhanced scalability, better user support and improved system openness are likely to be achieved with support for both completely- and incompletely-specified processes. As a consequence, workflow systems will be expected to be widely deployable to real world applications to support processes, which was infeasible before.

As computers become pervasive and better connected, the popularity of peer-to-peer computing has grown immensely. The sharing of unused resources at peers is desirable and practically important because they can collectively comprise a powerful system. The potential benefit, however, can be undermined by uncooperative behavior of some peers because they are managed individually and hence may not follow the expected protocols. To build robust systems, we must incorporate proper trust and incentive mechanisms so that peers would rather cooperate. In this dissertation, we demonstrate that building robust peer-to-peer information dissemination systems is important and viable, using four concrete cases. First, we investigate the incentive mechanism of BitTorrent, an exchange-based file distribution protocol. Our framework based on iterated prisoner's dilemma provides an insight into users' tension between eagerness to download and unwillingness to upload. By using both analytical and experimental approaches, we show that the current incentive mechanism of BitTorrent is susceptible to free riding. We propose an improved mechanism that punishes free riders effectively. Second, we present a trust-aware overlay multicast system that performs well in the presence of uncooperative nodes, which may block, delay, fabricate, or forge the messages they forward. We develop (1) a set of protocols that detect uncooperative behavior, (2) a scheme of trust value assignment according to the behavior of nodes, and (3) an algorithm that adapts the multicast tree based on trust values, all of which allows the system to remain stable and responsive over time. Third, we propose an alternative news feed dissemination system, called FeedEx, in which feed subscribers mesh into a network and exchange news feeds with neighbors. The collaborative exchange in FeedEx, with the help of the incentive-compatible design using the pair-wise fairness principle, reduces the server load and hence increases the scalability. Fourth, we introduce a new concept of peer-to-peer computing, that is, continual service using ephemeral servers. To this end, we develop a system model for the concept and implement a discrete-time simulator to find the conditions and the system support for eliciting cooperation. All four cases are substantiated by experimental results.