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2007 Euro American Conference on Telematics and Information Systems, EATIS 2007

作者： Garofalakis, John Giannakou, John Giannakoudi, Theodoula Sakkopoulos, Evangelos Research Academic Computer Technology Institute N. Kazantzaki str. 26500 Greece University of Patras Computer Engineering Informatics Dept 26500 Patras Greece

ISBN: (纸本)9781595935984

In this work, we introduce metrics and a proposed procedure to measure the popularity of a website. We present two novel metrics, Promo and Promo(2) that take advantage of the internal link structure of a website, in order to gain important navigation information. This is indicative of the difficulty the user encounters to access a particular link and can be combined with statistics gained from the log files as a metric of popularity. The two metrics propose a different definition of the popularity of a web object in order to generate a sorted list of promotion values for a website's links. We have delivered a web tool that implements the proposed procedure in order to facilitate a site designer to manipulate his/her web server log data, receive recommendations and popularity results and finally proceed with changes in the structure or position of links. Overall, the experimental study using user-based accesses log data, has been encouraging and it has verified the effectiveness of the Promo metrics.

关键词： Websites

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Enhancing Ns-2 with diffserv QoS features

Enhancing Ns-2 with diffserv QoS features

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10th Communications and Networking Simulation Symposium, CNS 2007, Part of the 2007 Spring Simulation Multiconference, SpringSim 2007

作者： Bouras, Ch. Primpas, D. Stamos, K. Research Academic Computer Technology Institute PO Box 1122 Patras Greece Computer Engineering and Informatics Dept. Univ. of Patras GR-26500 Patras Greece

ISBN: (纸本)1565553128

In this paper, we present work that we have carried out in extending the ns-2 simulator in order to study and validate Quality of Service issues and related architectures. In the case of the DiffServ framework, simulation is valuable since an analytical approach of mechanisms and services is infeasible due to the aggregation and multiplexing of flows. This paper covers work in extending ns-2 functionality towards the direction of realistic traffic generation and a series of mechanisms defined by the DiffServ architecture. We have also extended ns-2 with the functionality of Bandwidth Brokers, which are entities for managing the resources and negotiating end to end resource reservations between domains. The Bandwidth Broker ns-2 implementation is useful for studying the related architectures and admission control procedures.

关键词： Quality of service

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MBMS Power Planning in Macro and Micro Cell Environments

MBMS Power Planning in Macro and Micro Cell Environments

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IEEE Symposium on computers and Communications (ISCC)

作者： Antonios Alexiou Christos Bouras Vasileios Kokkinos Evangelos Rekkas Computer Engineering and Informatics Department University of Patras Greece Research Academic Computer Technology Institute Greece Research Academic Computer Technology Institute Greece and Computer Engineering and Informatics Department University of Patras Greece

Multimedia Broadcast Multicast Services (MBMS), introduced in Third Generation Partnership Project (3GPP) Release 6, is a point-to-multipoint downlink bearer service that addresses the need for the efficient usage of the expensive radio resources. Power control is one of the most important aspects in MBMS due to the fact that Node B's transmission power is a limited resource and must be shared among all MBMS users in a cell. Consequently, the analysis of transmitted power plays a fundamental role in the planning and optimization process of Universal Mobile Telecommunications System (UMTS) radio access networks. This paper investigates several factors affecting Node B's transmission power levels such as, cell deployment, propagation models, Quality of Service (QoS) requirements, users' distributions and mobility issues. Finally, different transport channels for the transmission of the multicast data over the UTRAN interfaces are considered.

关键词： Quality of service Digital multimedia broadcasting Multimedia communication Radio broadcasting Downlink Power control Power system planning Process planning 3G mobile communication Radio access networks

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Searchius: A Collaborative Search Engine

Searchius: A Collaborative Search Engine

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Current Trends in computer Science (ENC), Mexican International Conference on

作者： Athanasios Papagelis Christos Zaroliagis Department of Computer Engineering and Informatics Patras Greece Department of Computer Engineering and Informatics Research Academic Computer Technology Institute Patras Greece

Searchius is a collaborative search engine that produces search results based solely on user provided web-related data. We discuss the architecture of this system and how it compares to current state-of-the-art search engines. We show that the global users' preference over pages can be efficiently used as a metric of page quality, and that the inherent organization of the collected data can be used to discover related URLs. We also conduct an extensive experimental study, based on the web related data of 36483 users, to analyze the qualitative and quantitative characteristics of user collected URL collections, to investigate how well the users URL collections cover the web and discover the characteristics that affect the quality of the search results under the proposed setting.

关键词： Search engines Uniform resource locators informatics History Web pages Catalogs computer science International collaboration Data engineering computer architecture

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Load Distribution Fairness in P2P Data Management Systems

Load Distribution Fairness in P2P Data Management Systems

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International Conference on Data engineering

作者： Theoni Pitoura Peter Triantafillou Research Academic Computer Technology Institute and Computer Engineering and Informatics Department University of Patras Greece

ISBN: (纸本)1424408024

We address the issue of measuring storage, or query load distribution fairness in peer-to-peer data management systems. Existing metrics may look promising from the point of view of specific peers, while in reality being far from optimal from a global perspective. Thus, first we define the requirements and study the appropriateness of various statistical metrics for measuring load distribution fairness towards these requirements. The metric proposed as most appropriate is the Gini coefficient (G). Second, we develop novel distributed sampling algorithms to compute G on-line, with high precision, efficiently, and scalably. Third, we show how G can readily be utilized on-line by higher-level algorithms which can now know when to best intervene to correct load imbalances. Our analysis and experiments testify for the efficiency and accuracy of these algorithms, permitting the online use of a rich and reliable metric, conveying a global perspective of the distribution.

关键词： Peer to peer computing Distributed computing Load management Sampling methods technology management engineering management Testing Data engineering informatics Algorithm design and analysis

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X3D Multi-user Virtual Environment Platform for Collaborative Spatial Design

X3D Multi-user Virtual Environment Platform for Collaborativ...

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International Conference on Distributed Computing Systems Workshop

作者： Ch. Bouras Ch. Tegos V. Triglianos Th. Tsiatsos Computer Engineering and Informatics Department(CEID) University of Patras Greece Research Academic Computer Technology Institute Greece Department of Informatics Research Academic Computer Technology Institute (CTI) Aristotle University of Thessaloniki Greece

It is well known that both space and the spatial organization play an important role in our work and learning environments as well as in everyday life. There is a definite need for many persons to design their space along with an expert and to preview it in order to test its functionality. Many times there is a need for the inhabitants and workers to collaborate in order to co-design their space from distance. Multi-user 3D virtual environments are a powerful form of collaborative telecommunication applications, enabling the users to share a common three dimensional space and interact with each other as well as with the environment surrounding them, in order to collaboratively solve problems or aid learning processes. This paper presents the work done for extending a multi-user virtual environments platform, to support collaborative spatial design applications. Furthermore, a usage scenario is presented concerning the collaborative design of a classroom for educational purposes.

关键词： Virtual environment Collaboration Collaborative work informatics Design engineering Space technology Application software Testing Internet research and development

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Burstification effect on the TCP synchronization and congestion window mechanism

Burstification effect on the TCP synchronization and congest...

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International Conference on Broadband Networks (BroadNets)

作者： Kyriakos G. Vlachos Computer Engineering and Informatics Department & Research Academic Computer Technology Institute University of Patras Rio Greece

ISBN: (纸本)9781424414321

In this paper, we study the burstification effect on the TCP synchronization and TCP congestion window mechanism. It is shown that short assembly times are optimal for flows with similar characteristics, while large assembly time provide a higher notion of fairness. In addition, this paper analyzes the synchronization of multiple TCP flows when aggregated together over the same optical bursts. It is shown that there is a strong TCP synchronization effect upon burst losses, in the sense that flows’ windows increase/decrease simultaneously, resulting to a significant variation of outgoing traffic. These deficiencies may be dealt with employing a multi-queue burst assembly scheme with different timers and taking into account the TCP dynamics.

关键词： Assembly Delay Transport protocols Throughput Performance analysis informatics Image motion analysis Optical sensors Optical losses Traffic control

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A Power Control Scheme for Efficient Radio Bearer Selection in MBMS

A Power Control Scheme for Efficient Radio Bearer Selection ...

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IEEE International Symposium on World of Wireless Mobile and Multimedia Networks (WoWMoM)

作者： Antonios Alexiou Christos Bouras Evangelos Rekkas Research Academic Computer Technology Institute Greece and Computer Engineering and Informatics Department University of Patras Greece

This paper proposes a power control scheme for the efficient radio bearer selection in the Multimedia Broadcast/Multicast Service (MBMS) framework of Universal Mobile Telecommunications System (UMTS). The choice of the most efficient transport channel in terms ofpower consumption is a key point for the MBMS since a wrong transport channel selection for the transmission of the MBMS data could result to a significant decrease in the total capacity of the system. Diferent UMTS transport channels are examined and an algorithm that defines the switching point between dedicated and common radio bearers is proposed The proposed MBMSpower control scheme selects the transport channel that reduces the Node B's transmission power in every cell of the network with multicast users.

关键词： Power control 3G mobile communication Energy consumption Broadcasting Power engineering computing Multimedia communication Broadcast technology Multicast algorithms Videoconference Power engineering and energy

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Multiple-Input and Shared Buffer Architectures for Asynchronous Optical Burst Switching Networks

Multiple-Input and Shared Buffer Architectures for Asynchron...

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IEEE International Conference on Communications (ICC)

作者： K. Yiannopoulos E. Varvarigos K. Vlachos Computer Engineering and Informatics Department and Research Academic Computer Technology Institute University of Patras Rio Greece

In this paper, we present the architectural design of optical burst-buffers that can truly emulate input queuing and accommodate asynchronous burst operation. The architectural design uses wavelength converters and fixed feed-forward delay lines that are combined to form either a multiple-input buffer or a shared buffer. Both schemes are modular, allowing the logarithmic expansion of buffer size with the number of switching elements (wavelength converters).

关键词： Optical buffering Optical burst switching Optical wavelength conversion Delay lines Buffer storage Optical design Optical feedback Optical fiber networks Propagation delay Feedforward systems

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Deterministic optical quantum computer using photonic modules

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Physical Review A 2008年第3期78卷 032318-032318页

作者： Ashley M. Stephens Zachary W. E. Evans Simon J. Devitt Andrew D. Greentree Austin G. Fowler William J. Munro Jeremy L. O’Brien Kae Nemoto Lloyd C. L. Hollenberg Centre for Quantum Computer Technology The University of Melbourne Victoria 3010 Australia National Institute for Informatics 2-1-2 Hitotsubashi Chiyoda-ku Tokyo 101-8430 Japan Institute for Quantum Computing University of Waterloo Waterloo Ontario Canada N2L 3G1 Hewlett-Packard Laboratories Filton Road Stoke Gifford Bristol BS34 8QZ United Kingdom Centre for Quantum Photonics H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering University of Bristol Merchant Venturers Building Woodland Road Bristol BS8 1UB United Kingdom

The optical quantum computer is one of the few experimental systems to have demonstrated small scale quantum information processing. Making use of cavity quantum electrodynamics approaches to operator measurements, we detail an optical network for the deterministic preparation of arbitrarily large two-dimensional cluster states. We show that this network can form the basis of a large scale deterministic optical quantum computer that can be fabricated entirely on chip.

关键词： Quantum optics

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