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Computer Networks. 01/2010; 54:811-825.
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Proceedings of the 2009 International Conference on Grid Computing & Applications, GCA 2009, July 13-16, 2009, Las Vegas, Nevada, USA; 01/2009
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J. Parallel Distrib. Comput. 01/2009; 69:737-747.
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Security and Communication Networks. 01/2009; 2:654-668.
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MSN 2008, The 4th International Conference on Mobile Ad-hoc and Sensor Networks, Wuhan, China, December 10-12, 2008; 01/2008
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Proceedings of the International Conference on Parallel and Distributed Processing Techniques and Applications, PDPTA 2008, Las Vegas, Nevada, USA, July 14-17, 2008, 2 Volumes; 01/2008
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Computer Networks. 01/2008; 52:3017-3027.
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ABSTRACT: Scheduling strategies for on-demand data in broadcast systems typically consider how to minimize the wait time of the requests. When users' requests for data in a broadcast system have real-time constraints, scheduling strategies for such requests typically only consider how to minimize the number of deadlines missed. There are many applications with both real-time and non-real-time requests that would benefit from a broadcast scheduling strategy that considers both the timing constraints and the wait times of requests. We refer to such a broadcast environment as a mixed-type request broadcast environment. In this paper, we present an on-demand broadcast cost model for mixed-type broadcast environments that considers both the response time and number of deadlines missed. We propose a scheduling strategy for mixed-type broadcast systems, called the maximum paid cost first (MPCF) that is based on this cost model. The simulation results show that our MPCF strategy always achieves the best result for varying request arrival rates, ratio of non-real-time requests and real-time requests, and a weighted missed deadline value, when compared to existing broadcast strategies.
Global Telecommunications Conference, 2007. GLOBECOM '07. IEEE; 12/2007
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21th International Parallel and Distributed Processing Symposium (IPDPS 2007), Proceedings, 26-30 March 2007, Long Beach, California, USA; 01/2007
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Proceedings of the Global Communications Conference, 2007. GLOBECOM '07, Washington, DC, USA, 26-30 November 2007; 01/2007
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Proceedings of the 2006 International Conference on Grid Computing & Applications, GCA 2006, Las Vegas, Nevada, USA, June 26-29, 2006; 01/2006
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ABSTRACT: Data is typically replicated in a Data Grid to improve the job response time and data availability. Strategies for data replication in a Data Grid have previously been proposed, but they typically assume unlimited storage for replicas. In this paper, we address the system-wide data availability problem assuming limited replica storage. We describe two new metrics to evaluate the reliability of the system, and propose an on-line optimizer algorithm that can Minimize the Data Missing Rate (MinDmr) in order to maximize the data availability. Based on MinDmr, we develop four optimizers associated with four different file access prediction functions. Simulation results utilizing the OptorSim show our MinDmr strategies achieve better performance overall than other strategies in terms of the goal of data availability using the two new metrics.
Future Generation Computer Systems.
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ABSTRACT: Real-time database systems can have security constraints in addition to timing constraints. Such real-time systems are typically contained in environments that exhibit hierarchical propagation of information, where mandatory access control for security is required. Conventional multilevel secure (MLS) database models that implement mandatory access control are inadequate for time-critical applications and conventional real-time database models do not address security constraints. The objective of this work is to incorporate security constraints in real-time database systems in such a way that not only is security achieved, but achieving security does not degrade real-time performance significantly in terms of deadlines missed. We present two concurrency control algorithms for secure real-time databases: the Secure two-phase locking high priority (2PLHP) algorithm is based on a two-phase locking protocol and the Secure optimistic concurrency control (OPT) algorithm uses the properties of an optimistic concurrency protocol. We implement the two algorithms and study their performance using a real-time database system simulation model. Our study covers both soft and firm real-time databases. Results show that both the algorithms perform fairly well in terms of security and timeliness compared to non-secure algorithms. We show that achieving increased security does not necessarily mean an increased sacrifice in real-time performance.
Journal of Systems and Software.
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ABSTRACT: In addition to timing constraints, a real-time database has temporal consistency constraints for its temporal data. The temporal consistency constraints require the data to represent a state of the real-world that is up-to-date and also require data to represent past states of the real-world with values that are close in time. Factors, such as concurrency control, can cause transactions to miss their deadlines and data to become temporally inconsistent. Approximate query processing (AQP) has been proposed as a strategy to satisfy the timing constraints of real-time databases. Approximate answers are provided by AQP if it is not possible to produce an exact answer by a specified deadline. In this paper, we examine the temporal consistency of the data during traditional and AQP. Four metrics of temporal consistency are utilized to compare the age and dispersion of the data during traditional query processing (TQP) versus approximate query processing. Simulation results identify factors, such as the concurrency control algorithm, the number of transactions and the percentage of query transactions, that affect the temporal inconsistency of the data.
Journal of Systems and Software.
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ABSTRACT: People enjoy the convenience of on-line services, Automated Teller Machines (ATMs), and pervasive computing, but online environments, ATMs, and pervasive computing may bring many risks. In this paper, we discuss how to prevent users’ passwords from being stolen by adversaries. We propose a virtual password concept involving a small amount of human computing to secure users’ passwords in on-line environments, ATMs, and pervasive computing. We adopt user-determined randomized linear generation functions to secure users’ passwords based on the fact that a server has more information than any adversary does. We analyze how the proposed schemes defend against phishing, key logger, and shoulder-surfing attacks. To the best of our knowledge, our virtual password mechanism is the first one which is able to defend against all three attacks together.
Computer Communications.
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ABSTRACT: Approximate is a query processor that makes approximate answers available if part of the data base is unavailable or there is not enough time to produce an exact answer. The accuracy of the approximate answers produced improves monotonicaIly with the amount of data retrieved to produce the result. We describe the approximation semantics of Approximate that serves as the basis for meaningful approximations of both set- and single-valued queries. We show how APPROXIMATE is implemented to make effective use of semantic information, such as a distance function, to define and compare the accuracies of approximate answers with the exact answer.
Journal of Systems and Software.
