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28
Page migration in dynamic networks
, 2005
"... In the last couple of decades, network connected systems have gradually replaced centralized parallel computing machines. To provide smooth operation of network applications, the underlying system has to provide socalled basic services. One of the most crucial services is to provide a transparent a ..."
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In the last couple of decades, network connected systems have gradually replaced centralized parallel computing machines. To provide smooth operation of network applications, the underlying system has to provide socalled basic services. One of the most crucial services is to provide a transparent access to data like
Delayed Information and Action in OnLine Algorithms
 39th IEEE symposium on Foundations of Computer Science
, 1998
"... Most online analysis assumes that, at each time step, all relevant information up to that time step is available and a decision has an immediate effect. In many online problems, however, the time relevant information is available and the time a decision has an effect may be decoupled. For example, ..."
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Most online analysis assumes that, at each time step, all relevant information up to that time step is available and a decision has an immediate effect. In many online problems, however, the time relevant information is available and the time a decision has an effect may be decoupled. For example, when making an investment, one might not have completely uptodate information on market prices. Similarly, a buy or sell order might only be executed some time later in the future. We introduce and explore natural delayed models for several wellknown online problems. Our analyses demonstrate the importance of considering timeliness in determining the competitive ratio of an online algorithm. For many problems, we demonstrate that there exist algorithms with small competitive ratios even when large delays affect the timeliness of information and the effect of decisions.
On the Security of a Digital Signature with Message Recovery Using Selfcertified Public Key
 SOFT COMPUTING IN MULTIMEDIA PROCESSING SPECIAL ISSUE OF THE INFORMATICA JOURNAL
, 2005
"... Selfcertified public keys are proposed to eliminate the burden of verifying the public key before using. To alleviate reliance on system authority and strengthen the security of system, Chang et al propose a new digital signature schemes, no redundancy is needed to be embedded in the signed message ..."
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Selfcertified public keys are proposed to eliminate the burden of verifying the public key before using. To alleviate reliance on system authority and strengthen the security of system, Chang et al propose a new digital signature schemes, no redundancy is needed to be embedded in the signed messages in this scheme. Moreover, Chang et al claimed that the schemes are still secure even without the trustworthy system authority, and only the specified recipient can recover the message in his authentication encryption schemes. Unfortunately, In this work, we analyze the security of Chang et al scheme and show that if the system authority is trustless, the scheme is insecure, namely, the system authority can recover the message without the private key of the recipient in Chang ’ authentication encryption schemes. Finally, we propose an improved scheme to overcome the weakness of Chang et al scheme.
On the work function algorithm for two state task systems
, 2007
"... We revisit the known work function online algorithm WFA for metrical task systems in the special case when there are only two states. It is well known that this algorithm is 3 competitive. We offer a slightly modified version of this algorithm, and show that our version exactly mimics the migration ..."
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We revisit the known work function online algorithm WFA for metrical task systems in the special case when there are only two states. It is well known that this algorithm is 3 competitive. We offer a slightly modified version of this algorithm, and show that our version exactly mimics the migration pattern of the best possible offline algorithm, though the timing of the migration events is somewhat different in these two algorithms. We use this to give a refined bound on the cost of WFA in terms of the cost of the optimal offline algorithm. Specifically, we partition the cost of the optimal algorithm to a fixed cost F, inefficiency cost I and migration cost M. The cost of our algorithm is at most F + I + 3M. This implies that our version of WFA does not only have a worst case competitive ratio at most 3 (which is best possible) but additionally enjoys better competitive ratios on “typical” input sequences. The current study was motivated by practical problem. We present preliminary experimental evidence that indicates that the algorithm works well in practice. 1
Aspects of Network Design
, 2007
"... In this dissertation we study two problems from the area of network design. The first part discusses the multicommodity buyatbulk network design problem, a problem that occurs naturally in the design of telecommunication and transportation networks. We are given an underlying graph and associated ..."
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In this dissertation we study two problems from the area of network design. The first part discusses the multicommodity buyatbulk network design problem, a problem that occurs naturally in the design of telecommunication and transportation networks. We are given an underlying graph and associated with each edge of the graph, a cost function that represents the price of routing demand along this edge. We are also given a set of demands between pairs of vertices each of which needs to be satisfied by paying for sufficient capacity along a path connecting the vertices of the pair. In the multicommodity network design problem the objective is to minimize the cost of satisfying all demands. There are often situations where there is an initial fixed cost of utilizing an edge, or there is discounting or economies of scale that give rise to concave cost functions. We have an instance of the buyatbulk network design problem when the cost functions along all edges are concave. Unlike the case of linear cost functions, for which polynomial time algorithms exist, the buyatbulk network design problem is NPhard. We give the first nontrivial approx
Online Algorithms: A Study of GraphTheoretic Concepts
"... . In this paper we survey results on the design and analysis of online algorithms, focusing on problems where graphs and graphtheoretic concepts have proven particularly useful in the formulation or in the solution of the problem. For each of the problems addressed, we also present important ope ..."
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. In this paper we survey results on the design and analysis of online algorithms, focusing on problems where graphs and graphtheoretic concepts have proven particularly useful in the formulation or in the solution of the problem. For each of the problems addressed, we also present important open questions. 1 Introduction The traditional design and analysis of algorithms assumes that an algorithm, which generates output, has complete knowledge of the entire input. However, this assumption is often unrealistic in practical applications. Many of the algorithmic problems that arise in practice are online. In these problems the input is only partially available because some relevant input arrives only in the future and is not accessible at present. An online algorithm must generate output without knowledge of the entire input. Online problems arise in areas such as resource allocation in operating systems, data structuring, robotics, distributed computing and scheduling. We give some...
Object Grouping and Replication Algorithms for Word Wide Web
 INFORMATICA 29:347–356
, 2005
"... This paper presents an algorithm to group correlated objects that are most likely to be requested by a client in a single session. Based on these groups, a centralized algorithm that determines the placements of objects to a cluster of webservers is proposed to minimize latency. Due to the dynamic ..."
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This paper presents an algorithm to group correlated objects that are most likely to be requested by a client in a single session. Based on these groups, a centralized algorithm that determines the placements of objects to a cluster of webservers is proposed to minimize latency. Due to the dynamic nature of the Internet traffic and the rapid changes in the access pattern of the WorldWide Web, we also propose a distributed algorithm where each site relies on some collected information to decide what object should be replicated at that site. The performance of the proposed algorithms is evaluated through a simulation study.
Optimal Algorithms for Page Migration in Dynamic Networks
"... We present an extension of a classical data management subproblem, the page migration. The problem is investigated in dynamic networks, where costs of communication between different nodes may change with time. We construct asymptotically optimal online algorithms for this problem, both in determini ..."
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We present an extension of a classical data management subproblem, the page migration. The problem is investigated in dynamic networks, where costs of communication between different nodes may change with time. We construct asymptotically optimal online algorithms for this problem, both in deterministic and randomized scenarios. Key words: online algorithms, randomized algorithms, page migration, data management, dynamic networks 1