8229875
A Reputation-based Trust Management in Peer-to-Peer Network Systems
Peer-to-peer networks have gained a lot of attention over the last couple of years, mainly due to the popularity of the free multimedia file-sharing program Napster and a legal battle around it. Being open by nature P2P systems represent an ideal environment for various types of malicious intrusions. The problem of securing hosts on P2P network while keeping the openness of the system has been studied extensively over last couple of years but still remains open. Existing solutions based on reputation management either employ centralized algorithms or rely on peers' cooperation on the network. We describe a fully decentralized approach that allows computing peers' reputation based on the traffic between a node and its peers, independently of these peers willingness to cooperate in calculation of their reputation. 1 INTRODUCTION Peer-to-peer (P2P) network systems are increasingly gaining popularity on the Internet. These networks allow individual hosts (peers) to share and distribute various types of information over the Internet. By their nature, P2P networks are structured in a way that allows an open and unsupervised communication between peers. Therefore, these systems are vulnerable to various types of attacks, among which are denial-of-service attacks (DoS) and distribution of viruses. To protect themselves from malicious intentions, hosts should be able to identify reliable peers for communication. Identifying these peers is a challenging task in highly dynamic network environments like P2P networks. In this paper we suggest a solution to this problem based on the notion of trust. We propose a policy for managing traffic in peer-to-peer network based on peers' reputation. We also describe a model for computing this reputation using the trust score based on the peers' interaction with each other. Unlike most existing reputation-based models, our approach does not employ a centralized storage and only produces reputation scores on demand. The proposed solution is fully distributed and does not require any cooperation from the rest of the network. Our model aims to help users to select the most reliable peers whose past behavior shows willingness to participate in a proper functioning of the P2P system and at the same time to anticipate possible attacks from malicious peers by limiting their access to the victim peer's resources. In this paper we focus on a particular type of P2P systems, called Gnutella, which proved to be one of the most popular P2P systems. Furthermore, unlike other popular P2P applications such as KaZaa, the source …
2308501
A framework for parsing colonoscopy videos for semantic units
Colonoscopy is an important screening procedure for colorectal cancer. During this procedure, the endoscopist visually inspects the colon. Currently, there is no content-based analysis and retrieval system that automatically analyzes videos captured from colonoscopic procedures and provides a user-friendly and efficient access to important content. Such a system will be valuable for endoscopic research and education. The first necessary step for the analysis is parsing for semantic units. Since the characteristics of colonoscopy videos differ from those of videos studied in the literature, we introduce a new video parsing framework that includes: (i) a new scene definition and a new video parsing paradigm; (ii) a novel scene segmentation algorithm using audio analysis and finite state automata to recognize scenes and associated boundaries. Our experimental results show average precision and recall of 95% and 81%, respectively, for parsing scenes. The framework is extensible to videos captured from other endoscopic procedures such as upper gastrointestinal endoscopy, enteroscopy, cystoscopy, and laparoscopy.
14407932
Automatic measurement of quality metrics for colonoscopy videos
Colonoscopy is the accepted screening method for detection of colorectal cancer or its precursor lesions, colorectal polyps. Indeed, colonoscopy has contributed to a decline in the number of colorectal cancer related deaths. However, not all cancers or large polyps are detected at the time of colonoscopy, and methods to investigate why this occurs are needed. We present a new computer-based method that allows automated measurement of a number of metrics that likely reflect the quality of the colonoscopic procedure. The method is based on analysis of a digitized video file created during colonoscopy, and produces information regarding insertion time, withdrawal time, images at the time of maximal intubation, the time and ratio of clear versus blurred or non-informative images, and a first estimate of effort performed by the endoscopist. As these metrics can be obtained automatically, our method allows future quality control in the day-to-day medical practice setting on a large scale. In addition, our method can be adapted to other healthcare procedures. Last but not least, our method may be useful to assess progress during colonoscopy training, or as part of endoscopic skills assessment evaluations.
14348286
A Visual Model Approach for Parsing Colonoscopy Videos
Colonoscopy is an important screening procedure for colorectal cancer. During this procedure, the endoscopist visually inspects the colon. Currently, there is no content-based analysis and retrieval system that automatically analyzes videos captured from colonoscopic procedures and provides a user-friendly and efficient access to important content. Such a system will be valuable as an educational resource for endoscopic research, a platform to assess procedural skills for endoscopists, and a platform for mining for unknown abnormality patterns that may lead to colorectal cancer. The first necessary step for the analysis is parsing for semantic units. In this paper, we propose a new visual model approach that employs visual features extracted directly from compressed videos together with audio analysis to discover important semantic units called scenes. Our experimental results show average precision and recall of 93% and 85%, respectively.
14591533
Leveraging broadband access for true on-demand delivery of Internet videos
We consider in this paper how the increasingly popular broadband access can be leveraged for scalable and cost-effective video service. Although much work has been done for such service, the existing techniques either are not designed for on-demand video delivery, or do not take into account the vastly improved client receiving capability. In this paper, we address this problem and develop three novel video delivery techniques with two ultimate goals: minimizing service latency and maximize data sharing. With the new techniques, a client can be served as soon as server resource becomes available and meanwhile, all its receiving bandwidth can be used for data receiving. In particular, in the proposed dynamic scheduling algorithm, the efficiency of data sharing is further improved by also exploring server bandwidth for early delivery of video segments. This innovation is contradicted to the intuition that each video segment should be delivered as late as possible in order to maximize data sharing. We evaluate the performance of our new techniques using simulation and our study convincingly shows that with the new schemes, zero service latency can indeed be achieved with very minimal system resource.
271858
Providing scalable on-demand video services for heterogeneous receivers
To provide scalable video-on-demand services, precious system bandwidth must be shared among video requests. Although many efficient bandwidth-sharing techniques have been proposed, they are all designed for homogeneous receivers, i.e., the clients are assumed to have the same receiving bandwidth. For networks with client heterogeneity, these techniques either cannot work or have to compromise their performance. In this paper, we address this problem and propose an efficient solution allowing each client to use its whole receiving bandwidth to download data. To serve a client, the server first selects a set of serving channels for the client according to its actual receiving bandwidth. The video data needed for this client are then scheduled and dynamically adjusted for delivery over these channels. We evaluate the performance of the new technique using simulation and compare it with an existing scheme. Our study shows that by effectively leveraging client heterogeneity, the new technique achieves significantly smaller service latency
8690187
Distributed Simulation Using a Network of Processors
Abstract Simulation, particulary of networks of queues, is an application with a high degree of inherent parallelism and is of great practical interest. We hope to exploit this parallelism by performing simulations using a network of cheap, but slow, micro-processors. We define a taxonomy by which we classify a number of parameters of a distributed simulation method, and seek solutions to problems of synchronization, deadlock prevention and inter-process communication arising with various methods in each class of the taxonomy. We concentrate in particular on the class (loose, event-driven) which seems to possess the greatest potential parallelism, and on the class (scaled, tight, time-driven) which allows mock-up studies of real systems. We give algorithms for deadlock prevention and detection, and briefly discuss the design of a distributed operating system to support the simulation application. This research forms part of a joint program with the Dept. of Computer Sciences, University of Texas at Austin, directed by Prof. K.M. Chandy.
3873642
On staleness and the delivery of web pages
A popular technique to improve the scalability of a web based system is caching at proxy servers. Caching has the drawback that a cached page becomes stale when the page is updated at the web server. In some cases, staleness may not be completely avoided because the server may not wish to expend the processing and communication resources required to transmit all the updates immediately. In general, if updates are transmitted less frequently, the staleness will tend to increase, but the amount of resources consumed will be reduced. The tradeoff between resource consumption and staleness is investigated. A measure of staleness is defined and optimization problems are formulated. The solutions to these problems allow one to come up with an optimal strategy for transmitting page updates. Numerical examples showing the resource consumption/staleness tradeoff are presented.
3837698
On Staleness and the Delivery of Web Pages
A popular technique to improve the scalability of a web based system is caching at proxy servers. Caching has the drawback that a cached page becomes stale when the page is updated at the web server. In some cases, staleness may not be completely avoided because the server may not wish to expend the processing and communication resources required to transmit all the updates immediately. In general, if updates are transmitted less frequently, the staleness will tend to increase, but the amount of resources consumed will be reduced. The tradeoff between resource consumption and staleness is investigated. A measure of staleness is defined and optimization problems are formulated. The solutions to these problems allow one to come up with an optimal strategy for transmitting page updates. Numerical examples showing the resource consumption/staleness tradeoff are presented.
17359298
Queueing Network Modeling of Computer Communication Networks
The application of queueing network models to the performance analysis of messageswitched (or packet-switched) commumcatmn networks m surveyed. The main topics covered are the analysis of end-to-end delay and the analysis of buffer management schemes. A brief discussmn on flow control is also included. A queueing network model is developed for a simple user-resource network. The mean response time of a host computer m this network is illustrated by a numerical example.
2430654
Watermarking graph partitioning solutions
The authors introduce an Intellectual Property Protection (IPP) technique for graph partitioning which watermarks solutions to the graph partitioning problems so that they carry an author's signature. This technique is completely transparent to the actual computer-aided design tool which does the partitioning and is implemented by preprocessing and postprocessing alone. The authors propose five different schemes for the watermarking of partitioning solutions. The goal is to construct a partitioning solution which not only has a small edge cut, but also encodes the signature of the author. The key idea of all of our schemes is to map the signature into a set of constraints and then satisfy a disproportionate number of these constraints. Four of our schemes are based upon the idea of encouraging groups of vertices to be in the same partition. The fifth is based upon the encouragement of certain edges to be cut by the partitioning. The fifth scheme shows superior performances on all of the cases which we tested, including both two-way and multiway partitioning. The watermarking scheme produces solutions that have very low-quality degradation levels, yet carry signatures that are convincingly unambiguous, extremely unlikely to be present by coincidence and difficult to detect or remove without completely resolving the partitioning problem.