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Evaluation of teleteaching services over ATM and IP networks

Telematics and informatics 2003年第1期20卷 1-18页

作者： Bouras, Ch. Gkamas, A. Kapoulas, V. Tsiatsos, Th. Computer Technology Institute Riga Feraiou 61 GR-26221 Patras Greece Computer Engineering and Informatics Department University of Patras Riga Feraiou 61 GR-26221 Patras Greece

This paper presents the components of a synchronous teleteaching application, their underlying technology and their interaction with network services. In addition, it presents the architecture and design of a synchronous teleteaching application used over the public ATM network in Greece. This paper presents various teleteaching scenarios over an ATM network infrastructure with the use of native ATM and IP over ATM. In each scenario we present the standards used, the logical components, the resource demands (network and equipment) and its special characteristics. For each scenario we give detailed information about the transmission and frame rates and the video delay. The main result of our experiments is that broadband networks offer many capabilities for high quality teleteaching, and generally speaking, high quality telematic services. © 2002 Elsevier Science Ltd. All rights reserved.

关键词： computer aided instruction

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Multi-user layer in the EVE distributed virtual reality platform

Multi-user layer in the EVE distributed virtual reality plat...

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International Conference on Distributed Computing Systems Workshop

作者： C. Bouras D. Psaltoulis C. Psaroudis T. Tsiatsos Computer Engineering and Informatics Department University of Patras Greece Research Academic Computer Technology Institute Greece

In this paper, we present the design and implementation of a VRML97 multi-user layer, which is introduced in the EVE distributed virtual reality platform. Main consideration of our multi-user extension is the ease of transforming single-user virtual worlds to multi-user virtual worlds, as well as the conformity with any standard VRML97 browser. Furthermore, we present the EVE's communication platform, which can be used in order to support Collaborative Virtual Environments (CVEs). Main issues regarding the effective network communication as well as the initialization of the 3D scene are discussed in this paper.

关键词： Virtual reality Distributed computing informatics Virtual environment Design engineering Layout Space technology Collaboration User interfaces Web sites

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Issues for the performance monitoring on networked virtual environments: the case of EVE

Issues for the performance monitoring on networked virtual e...

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International Conference on Telecommunications (ConTEL)

作者： C. Bouras E. Giannaka Th. Tsiatsos Research Academic Computer Technology Institute Computer Engineering and Informatics Department University of Patras Patras Greece

The wide expansion and increasing demand for networked virtual environments resulted in efforts for the optimization of these environments with the enhancement of advanced features, which offered extended functionality and created an improved sense of realism. However, the added functionality often creates resource overhead both in the system as well as in the network host, which results in performance reduction. This paper presents such a networked virtual environment and based on the system's architecture tries to trace down with the time and recourse consuming parameters and proposes models on which a networked virtual environment, like the one presented, could achieve optimization of its performance.

关键词： computer aided software engineering Virtual environment computer networks Condition monitoring Virtual reality computerized monitoring informatics Computational modeling computer simulation System performance

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Competitive video on demand schedulers for popular movies

Competitive video on demand schedulers for popular movies

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作者： Bouras, Christos Kapoulas, Vaggelis Pantziou, Grammati Spirakis, Paul Research Academic Computer Technology Institute 2 Riga Feraiou 61 262 21 Patras Greece Department of Computer Engineering and Informatics University of Patras 265 00 Rion-Patras Greece Department of Informatics Technological Education Institute of Athens Ag. Spyridonos Str. 122 10 Egaleo-Athens Greece

In this paper we investigate the online video on demand problem, namely having to accept or reject a request for a movie without knowing the future requests. We present online movie-scheduling schemes that implement the principles of refusal by choice and delayed notification. A novel way to schedule movies that exploits the knowledge of the distribution of the preference of requests for movies, is shown to have a competitive ratio that outperforms all the previously known schemes in practical situations. In fact, our scheduler has a competitive ratio bounded above by a constant, independent of the number of the users, channels, or movies, in the case that a large fraction of the requests tends to concentrate in a small number of movies. We extend our approach by presenting an "adaptive" randomized scheduler which initially is not aware of the movie popularities but it adapts to it, and achieves the same asymptotic competitive ratio. © 2002 Elsevier Science B.V. All rights reserved.

关键词： Competitive ratio Online scheduling algorithm Probability distribution Video on demand

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Building e-learning communities: the case of VirRAD

Building e-learning communities: the case of VirRAD

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International Conference on Advanced Learning Technologies (ICALT)

作者： Ch. Bouras El. Giannaka V. Kapoulas M. Nani Th. Tsiatsos Computer Engineering and Informatics Department (CEID) University of Patras Greece Research Academic Computer Technology Institute Greece

We discuss the development of virtual communities and especially e-learning communities. In particular, we are inspired by VirRAD European project, and we present the intermediate results that have raised from the def... 详细信息

关键词： Electronic learning computer aided software engineering computer aided instruction Courseware Collaborative work informatics Environmental economics Virtual reality Vocational training Professional communication

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Blind image-adaptive watermarking

Blind image-adaptive watermarking

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IEEE International Conference on Electronics, Circuits and Systems (ICECS)

作者： I. Karybali K. Berberidis Department of Computer Engineering and Informatics and Research Academic Computer Technology Institute / Research and Development University of Patras Rio-Patras Greece

In this paper a new blind image-adaptive watermarking technique is proposed. The main contributions in this work are the following. First, a new spatial mask taking into account the Human Visual System (HVS) properties, is proposed. The mask is constructed based on the local variance of the cover image prediction error sequence. Second, an improved detection scheme has been developed, which is blind, in the sense that no knowledge concerning the cover image is required. The similarity measure used in the detector is the normalized correlation between the reproduced watermark and the prediction error of the watermarked and possibly attacked image (instead of the image itself). Due to the above modifications the proposed technique exhibits superior performance as compared to the conventional HVS-based blind adaptive watermarking. This performance improvement has been justified theoretically and verified through extensive simulations. In particular, the proposed technique is robust to additive white noise, JPEG and Wavelet compression, filtering etc.

关键词： Watermarking Humans Detectors Additive white noise Transform coding Image coding Filtering Image quality Robustness informatics

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From IPv4 to IPv6: the case of OpenH323 library

From IPv4 to IPv6: the case of OpenH323 library

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Workshops on Applications and the Internet (SAINT)

作者： Ch. Bouras A. Gkamas K. Stamos Computer Engineering and Informatics Department University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

We discuss our experience form porting the OpenH323 platform to IPv6. We briefly discuss the structure of the platform, and we present the various problems we faced and choices we made, regarding the easiest approach to the porting procedure, the compatibility with earlier, IPv4-only versions of the platform, the existence of tools that could aid us with the porting task and the verification of results. We believe that the results of our effort can serve as guidelines for other similar projects and we present a general methodology which might be applicable to similar porting projects.

关键词： computer aided software engineering Libraries Protocols Guidelines Operating systems informatics Shape Internet IP networks Costs

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Deployment of a DiffServ-based priority service in a MAN/WAN environment

Deployment of a DiffServ-based priority service in a MAN/WAN...

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International Conference on Advanced Information Networking and Applications (AINA)

作者： C. Bouras A. Sevasti Department of Computer Engineering and Informatics University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

The increased need for quality of service (QoS) in today's networks has concentrated a lot of research and implementation efforts. Particular interest exists for the exploitation of the DiffServ framework towards the provision of qualitative services in MAN and WAN worldwide. Although individual mechanisms have been widely investigated, not many references to studies combining all levels of priority and QoS provisioning exist. This work aims at presenting a thorough and unified approach to the dimensioning and provisioning of a high priority service for high-quality demanding traffic over a MAN/WAN environment. Our approach anticipates for bounds in specific quality metrics and is demonstrated by the experimental case-study of a high-priority service over a MAN topology.

关键词： Wide area networks Quality of service Telecommunication traffic Diffserv networks Traffic control Gold Delay Aggregates computer networks Topology

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Performance analysis for a DiffServ-enabled network: the case of relative service

Performance analysis for a DiffServ-enabled network: the cas...

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IEEE International Symposium on Network Computing and Applications

作者： C. Bouras A. Sevasti Department of Computer Engineering and Informatics University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

A lot of research work has recently focused on the exploitation of the DiffServ framework towards building reliable networking services that provide deterministic quality guarantees. In this work we are attempting to devise a DiffServ-based service model for relative differentiation of traffic in a network serving aggregated traffic. The service model proposed aims at providing a minimum capacity during congestion and a bounded average end-to-end delay to profile-conforming traffic, obtaining thus a relatively better performance when compared to the best-effort service. We provide the framework on which the proposed service model is based and we present results from its deployment in a simulation environment.

关键词： Performance analysis computer aided software engineering Diffserv networks Telecommunication traffic Traffic control computer networks Delay Quality of service Reliability engineering informatics

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A sleep-awake protocol for information propagation in smart dust networks

A sleep-awake protocol for information propagation in smart ...

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International Parallel and Distributed Processing Symposium, IPDPS 2003

作者： Chatzigiannakis, Ioannis Nikoletseas, Sotiris Computer Technology Institute P.O. Box 1122 Patras26221 Greece Computer Engineering and Informatics Department University of Patras Patras26500 Greece

ISBN: (纸本)0769519261

Smart dust is a set of a vast number of ultra-small fully autonomous computing and communication devices, with very restricted energy and computing capabilities, that co-operate to quickly and efficiently accomplish a large sensing task. Smart dust can be very useful in practice i.e. in the local detection of a remote crucial event and the propagation of data reporting its realization. In this work we continue our effort towards the research on smart dust from a basic algorithmic point of view. Under a simple but realistic model for smart dust we present an interesting problem, which is how to propagate efficiently information on an event detected locally. Then we present anew smart dust protocol, which we call the "Sleep-Awake" protocol, for information propagation that explicitly uses the energy saving features (i.e. the alteration of sleeping and awake time periods) of the smart dust particles. By using both some simple probabilistic analysis and extensive experiments, we provide some first concrete results for the success probability and the time and energy efficiency of the protocol, in terms of parameters of the smart dust network. We note that the study of the interplay of these parameters allows us to program the smart dust network characteristics accordingly. © 2003 IEEE.

关键词： Energy efficiency

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