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International Conference on Broadband Networks (BroadNets)

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

The efficient transmission of TCP traffic over OBS networks is a challenging problem, due to the high sensitivity of TCP congestion control mechanism to losses. In this work, we propose solutions to this problem, through the burst assembly and scheduling mechanism of OBS. We investigate and propose algorithms to achieve performance enhancements for TCP traffic by taking into account TCP state information. We prove our claims with references to well-established TCP models, and validate the proposed algorithms through simulations.

关键词： Assembly Scheduling algorithm Communication system traffic control Delay Protocols Throughput Traffic control Optical sensors computer networks Propagation losses

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Cross layer RWA in WDM networks: Is the added complexity useful or a burden?

Cross layer RWA in WDM networks: Is the added complexity use...

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International Conference on Transparent Optical Networks

作者： K. Christodoulopoulos P. Kokkinos K. Manousakis E. A. Varvarigos Computer Engineering and Informatics Department University of Patras Greece Research Academic Computer Technology Institute Patra Greece

ISBN: (纸本)9781424448258

In transparent wavelength routed optical networks, the signal quality degrades due to physical layer impairments. Certain physical effects make routing decisions made for one lightpath affect and be affected by the decisions for other lightpaths. To safely establish a lightpath for a new connection two main approaches can be used. The most common approach is to select a lightpath that has acceptable transmission quality under the worst case interference assumption. This ensures that the selected lightpath will not become infeasible due to the possible establishment of future interfering connections, but it sacrifices candidate path space for a quick and stable lightpath selection process. The second approach is to consider the actual current network utilization and account for the interference among lightpaths so as to perform a cross layer optimization between the network and physical layers. In the latter approach, the algorithm has to evaluate and check if the establishment of the new lightpath turns infeasible some of the already established connections. The question that arises is whether the performance benefits obtained through the second approach are worth the added complexity introduced by the cross-layer optimization required.

关键词： Cross layer design WDM networks Physical layer Interference computer networks Optical computing Physics computing Wavelength routing Optical fiber networks Degradation

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An Efficient Mechanism for Power Control Optimization in MBMS Enabled UTRAN

An Efficient Mechanism for Power Control Optimization in MBM...

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IEEE Conference on Wireless Communications and Networking

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

This paper proposes a power control mechanism for the efficient radio bearer selection in the multimedia broadcast/multicast service (MBMS) framework of Universal Mobile Telecommunications System (UMTS). The selection of the most efficient transport channel in terms of power consumption is a key point for MBMS enabled UMTS networks, 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 network. Different UMTS transport channels and power saving techniques are examined and an algorithm that selects the most efficient combination of the above parameters is proposed. The proposed MBMS power control mechanism selects the transport channel that minimizes the base station's transmission power in every cell of the network that serves multicast users.

关键词： Power control 3G mobile communication Multimedia communication Power engineering computing Telecommunication computing Digital multimedia broadcasting Broadcast technology Resource management Radio access networks Speech analysis

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Multi-Parametric Online RWA Based on Impairment Generating Sources

Multi-Parametric Online RWA Based on Impairment Generating S...

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GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference

作者： P. Kokkinos K. Christodoulopoulos K. Manousakis E. A. Varvarigos Computer Engineering and Informatics Department University of Patras Greece Research Academic Computer Technology Institute Patra Greece

We propose and evaluate an impairment-aware multi-parametric routing and wavelength assignment algorithm for online traffic in transparent optical networks. In such networks the signal quality of transmission degrades due to physical layer impairments. In the multi-parametric approach, a vector of cost parameters is assigned to each link, from which the cost vectors of candidate lightpaths are calculated. In the proposed scheme the cost vector includes impairment generating source parameters, such as the path length, the number of hops, the number of crosstalk sources and other inter-lightpath interfering parameters, so as to indirectly account for the physical layer effects. For a requested connection the algorithm calculates a set of candidate lightpaths, whose quality of transmission is validated using a function that combines the impairment generating parameters. For selecting the lightpath we propose and evaluate various optimization functions that correspond to different IA-RWA algorithms. Our performance results indicate that the proposed algorithms utilize efficiently the available resources and minimize the total accumulated signal degradation on the selected lightpaths, while having low execution times.

关键词： Costs Optical fiber networks Physical layer Degradation Repeaters Optical receivers computer networks Optical computing Wavelength routing Wavelength assignment

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Ontology engineering

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Nature Biotechnology 2010年第2期28卷 128-130页

作者： Alterovitz, Gil Xiang, Michael Hill, David P. Lomax, Jane Liu, Jonathan Cherkassky, Michael Dreyfuss, Jonathan Mungall, Chris Harris, Midori A. Dolan, Mary E. Blake, Judith A. Ramoni, Marco F. Children's Hospital Informatics Program Harvard-MIT Division of Health Sciences and Technology Harvard Medical School Boston MA United States Partners Healthcare Center for Personalized Genetic Medicine Boston MA United States Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA United States Jackson Laboratory Bar Harbor ME United States EMBL-EBI Wellcome Trust Genome Campus Hinxton United Kingdom Department of Biology Massachusetts Institute of Technology Cambridge MA United States Lawrence Berkeley National Laboratory Berkeley CA United States

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Experimental Evaluation of Duplicate Insensitive Counting Algorithms

Experimental Evaluation of Duplicate Insensitive Counting Al...

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Panhellenic Conference on informatics (PCI)

作者： Michael Resvanis Ioannis Chatzigiannakis Department of Computer Engineering and Informatics University of Patras Patras Greece Research Academic Computer Technology Institute and Department of Computer Engineering and Informatics University of Patras Patras Greece

Online and realtime counting and estimating the cardinality of sets is highly desirable for a large variety of applications, representing a foundational block for the efficient deployment and access of emerging Internet scale information systems. In this work we implement three well known duplicate insensitive counting algorithms and evaluate their performance in a testbed of resource-limited commercial off-the-shelf hardware devices. We focus on devices that can be used in wireless mobile and sensor applications and evaluate the memory complexity, time complexity and absolute error of the algorithms under different realistic scenario. Our findings indicate the suitability of each algorithm depending on the application characteristics.

关键词： informatics Frequency estimation Hardware Peer to peer computing Sensor systems Aggregates Statistics Application software Internet Information systems

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Cross layer optimization of static lightpath demands in transparent WDM optical networks

Cross layer optimization of static lightpath demands in tran...

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IEEE (first ITW conference of the year) Information Theory Workshop (ITW)

作者： K. Christodoulopoulos K. Manousakis E. A. Varvarigos Department of Computer Engineering and Informatics Research Academic Computer Technology Institute University슠of슠Patras Patra Greece

We consider the offline version of the impairment-aware routing and wavelength assignment (IA-RWA) problem in transparent all-optical networks as a cross layer optimization problem. In optical networks and in the absence of regenerators, optical signal quality degrades due to physical layer impairments. We initially present an algorithm for solving the RWA problem based on an LP relaxation formulation that has acceptable integrality performance. To account for signal degradation due to physical layer impairments we extend our RWA formulation and constrain the interference among lightpaths using noise variance related parameters. The objective of the resulting optimization problem is not only to serve the connection requests by minimizing the number of utilized wavelengths, but also to select lightpaths that have acceptable physical layer performance.

关键词： Cross layer design Wavelength division multiplexing WDM networks Optical fiber networks Physical layer Repeaters Degradation Wavelength routing Wavelength assignment All-optical networks

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Personalized News Search in WWW: Adapting on user's behavior

Personalized News Search in WWW: Adapting on user's behavior

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International Conference on Internet and Web Applications and Services (ICIW)

作者： Christos Bouras Vassilis Poulopoulos Panagiotis Silintziris Research Academic Computer Technology Institute Rio-Patras Greece Computer Engineering and Informatics Department Rio-Patras Greece

Personalized Web Search becomes nowadays a promising option in the field of Information Retrieval and search engines design by improving both output quality and user experience. In this paper, we present and evaluate the subsystem, which conducts the Advanced and Personalized search of PeRSSonal, a web-based mechanism for the retrieval, processing and presentation of articles and RSS feeds collected from major news portals of the Internet. The proposed technique uses information explicitly provided by the user in his profile as well as information that the mechanism can learn from the user's behavior during his search and browsing sessions in the system. As this behavior dynamically evolves, the same happens to the user's interests under the prism of the search engine. By adopting this user-centric approach, we manage to present the user with better-refined and more focused results, incorporating his personal preferences to the output. The algorithm operates not in a stand-alone manner but it co-operates and binds with the rest of modules of PeRSSonal in order to accomplish maximum integration with the system. Furthermore, we introduce an enhancement in the search function, based on cached results from past search sessions of each user individually.

关键词： Article search engine Personalized search PeRSSonal

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Capturing User Session Orientation Based on Semantic Analysis and Concept Taxonomy

Capturing User Session Orientation Based on Semantic Analysi...

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Balkan Conference in informatics (BCI)

作者： John Garofalakis Theodoula Giannakoudi Danai Vergeti Computer Engineering & Informatics Department University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

In this work, we propose a Web personalization methodology by detecting the user navigation's orientation. To this goal, we track user's hits and define whether a user specializes or generalizes his navigation through semantics analysis of the pages in his session window. An algorithm of capturing user session orientation based on a concept taxonomy is proposed. Finally, a method is presented which proposes useful recommendation to the user to improve his Web search. The experimental outcomes satisfied the prospective results. We believe that our technique could become a useful tool for navigation refinement. Furthermore, this work bridges search engine query refinement and browsing reformulation techniques.

关键词： Taxonomy Search engines Navigation Web search Web pages informatics Semantic Web Information retrieval Ontologies Bridges

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Simulcast transmission for video applications: Performance evaluation with an integrated simulation environment

Simulcast transmission for video applications: Performance e...

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International Symposium on Performance Evaluation of computer & Telecommunication Systems SPECTS

作者： Christos Bouras Georgios Kioumourtzis Apostolos Gkamas Computer Engineering and Informatics Department University of Patras Rion Greece Research Academic Computer Technology Institute Rion Greece

This paper presents the performance evaluation of a multi-rate multicast protocol named adaptive smooth simulcast protocol (ASSP) for simulcast video transmission. ASSP implements a single rate TCP-friendly protocol as the underlying congestion control mechanism for each simulcast stream. ASSP is built on top of the RTP/RTCP protocol and exploits the RTCP sender and receiver reports for the dissemination of feedback information. The key attributes of ASSP are: a) TCP-friendly behavior, b) adaptive per-stream transmission rates, c) adaptive scalability to large sets of receivers and finally d) smooth transmission rates that are suitable for multimedia applications. We evaluate the performance of ASSP under an integrated simulation environment, which extends ns-2 and Evalvid-RA into the multicast domain with the use of RTP/RTCP protocols. Simulations conducted under this environment combine the measurements of network metrics along with objective evaluation criteria on the perceived video quality by the end user.

关键词： Streaming media Multicast protocols Computational modeling Proposals Transport protocols computer simulation Scalability Bandwidth Application software informatics

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