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International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP

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

We design and implement an algorithm for solving the static RWA problem based on an LP relaxation formulation. This formulation is capable of providing integer optimal solutions despite the absence of integrality constraints for a large subset of RWA input instances. In static RWA there is no a-priori knowledge of the channels usage and the interference among them cannot be avoided once the solution has been found. To take into consideration adjacent channel interference, we extend our formulation and model the interference by a set of analytical formulas as additional constraints on RWA.

关键词： Interference Optical fiber networks Interchannel interference Routing Wavelength assignment Wavelength division multiplexing Modulation

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Comparison of Routing and Wavelength Assignment Algorithms in WDM Networks

Comparison of Routing and Wavelength Assignment Algorithms i...

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IEEE GLOBECOM 2008 - 2008 IEEE Global Telecommunications Conference

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

We design and implement various algorithms for solving the static RWA problem with the objective of minimizing the maximum number of requested wavelengths based on LP relaxation formulations. We present a link formulation, a path formulation and a heuristic that breaks the problem in the two constituent subproblems and solves them individually and sequentially. The flow cost functions that are used in these formulations result in providing integer optimal solutions despite the absence of integrality constraints for a large subset of RWA input instances, while also minimizing the total number of used wavelengths. We present a random perturbation technique that is shown to increase the number of instances for which we find integer solutions, and we also present appropriate iterative fixing and rounding methods to be used when the algorithms do not yield integer solutions. We comment on the number of variables and constraints these formulations require and perform extensive simulations to compare their performance to that of a typical min-max congestion formulation.

关键词： Wavelength routing Wavelength assignment WDM networks Telecommunication traffic Wavelength division multiplexing Optical fiber networks Optical fiber communication computer networks Algorithm design and analysis Cost function

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Routing and scheduling in grids

Routing and scheduling in grids

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International Conference on Transparent Optical Networks

作者： Konstantinos Christodoulopoulos Emmanouel Varvarigos Computer Engineering and Informatics Department University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

We propose QoS-aware scheduling algorithms for grid networks that are capable of optimally or near-optimally assigning computation and communication tasks to grid resources. The routing and scheduling algorithms to be presented take as input the resource utilization profiles and the task characteristics and QoS requirements, and co-allocate resources while accounting for the dependencies between communication and computation tasks.

关键词： Availability Processor scheduling Clustering algorithms Routing Heuristic algorithms Quality of service Delay

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A trusted architectural model for interconnecting testbeds of wireless sensor networks

A trusted architectural model for interconnecting testbeds o...

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International Symposium on Electronics in Marine (ELMAR)

作者： Ioannis Chatzigiannakis Vasiliki Liagkou Paul G. Spirakis Department of Computer Engineering and Informatics University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

ISBN: (纸本)9781424433643

Designing wireless sensor networks is inherently complex; many aspects such as energy efficiency, limited resources, decentralized collaboration, fault tolerance have to be tackled. To be effective and to produce applicable results, fundamental research has to be tested, at least as a proof-of-concept, in large scale environments, so as to assess the feasibility of the new concepts, verb their large scale effects (not only at technological level, but also as for their foreseeable implications on users, society and economy) and derive further requirements, orientations and inputs for the research. In this paper we focus on the problems of interconnecting existing testbed environments via the Internet and providing a virtual unifying laboratory that will support academia, research centers and industry in their research on networks and services. In such a facility important issues of trust, security, confidentiality and integrity of data may arise especially for commercial (or not) organizations. In this paper we investigate such issues and present the design of a secure and robust architectural model for interconnecting testbeds of wireless sensor networks.

关键词： Testing Wireless sensor networks Large-scale systems Energy efficiency Collaboration Fault tolerance IP networks Web and internet services Data security Robustness

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Smooth Multicast Congestion Control for Adaptive Multimedia Transmission

Smooth Multicast Congestion Control for Adaptive Multimedia ...

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Conference on Next Generation Internet Networks, NGI

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

In this paper we introduce an equation-based smooth multicast congestion control for adaptive multimedia transmission over best-effort wired networks. Target of the proposed schema is (a) smooth transmission rate, in order to minimize the audio-video (AV) encoding and decoding distortion and (b) TCP friendly transmission. The "smoothness" lays in the way the TCP-friendly transmission rate is filtered. We integrate the congestion control functions in the RTP protocol and use the RTCP sender and receiver reports to provide the necessary feedback information for the sender's adaptive transmission rate. The performance evaluation of the smooth adaptation and TCP-friendliness is conducted through a number of simulations with the network simulator software (ns2). Our intention is to use this congestion control in the context of a proposed framework for multimedia transmission over wired and wireless networks.

关键词： Programmable control Adaptive control Bandwidth Feedback Multicast protocols Delay Decoding Equations Data communication Wireless application protocol

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Correction to “Statistical Approach to Color Quality of Solid-State Lamps”

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IEEE Journal of Selected Topics in Quantum Electronics 2009年第5期15卷 1542-1542页

作者： Arturas Zukauskas Rimantas Vaicekauskas Feliksas Ivanauskas Henrikas Vaitkevicius Pranciskus Vitta Michael S. Shur Institute of Materials Science and Applied Research Vilnius University Vilnius Lithuania Faculty of Mathematics Informatics Vilnius University Vilnius Lithuania Department of Electrical Computer and Systems Engineering Rensselaer Polytechnic Institute Troy NY USA

In the above-named work [ibid., vol. 15, no. 4, pp. 1189-1198, Jul.-Aug. 2009], the biographical information for Dr. Michael S. Shur was incorrect. The corrected biographical information is printed here.

关键词： Color Biographies Electron devices Conferences Patents High-speed electronics Technological innovation

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A novel power counting mechanism for enhanced MBMS performance in UMTS networks

IFIP Advances in Information and Communication Technology

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IFIP Advances in Information and Communication technology 2008年 284卷 57-68页

作者： Alexiou, Antonios Bouras, Christos Rekkas, Evangelos Computer Engineering and Informatics Department University of Patras Greece Research Academic Computer Technology Institute 26500 Rio Patras Greece

ISBN: (纸本)9780387848389

One of the key objectives of Universal Mobile Telecommunications System (UMTS) is the realization of enhanced end-user experience through the provision of rich multimedia services, ensuring in parallel an economical delivery cost for service providers. Multimedia Broadcast/Multicast Services (MBMS) framework of UMTS epitomizes the increasing popularity of such applications by efficiently delivering multimedia traffic to a large number of users and optimizing the radio interface of UMTS networks. For exploiting resource efficiency, MBMS specifications consider the Counting Mechanism which decides whether it is more economic to deliver MBMS multicast traffic over point-to-point (PTP) or point-to multipoint (PTM) bearers. However, the necessity to further improve MBMS resource efficiency and integrate new technologies such as High Speed Downlink Packet Access (HSDPA) stresses the need for an advanced Counting Mechanism. To this direction, in this paper we propose a novel Power Counting Mechanism which performs optimal power resource utilization and incorporates the HSDPA broadband extension of UMTS for enhanced performance. © 2008, IFIP International Federation for Information Processing. All rights reserved.

关键词： Universal Mobile Telecommunications System

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System's Design and Implementation for Easy Creation of Mobile Commerce Systems

System's Design and Implementation for Easy Creation of Mobi...

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

作者： John Garofalakis Flora Oikonomou Vasilios Stefanis Computer Engineering and Informatics Department University of Patras Greece Academic Computer Technology Institute Patras Greece

Mobile commerce (m-commerce) is a rather new field in the business world. It depends on wireless networks for accessing the Internet from mobile devices and for exchanging data between such devices. Wireless technologies on the one hand evolve rapidly and are met in many different applications. On the other hand a plethora of factors encourage market to make advances towards the m-commerce market. New ideas about m-commerce services and applications find acceptance by the business world and by users. Unfortunately not all users know how to create m-commerce services and applications. Thus a system which can easily create mobile commerce systems can be proved very helpful. In this paper we present a system which can create other m-commerce systems in a user friendly way. The system is meant to be used in the m-commerce market as a mean of developing hotel Websites and mobile sites. It uses a simple form which guides the user to create fully functional websites and mobile sites. We focus on implementation issues and evaluate our system after testing it. Finally, conclusions are extracted and future work is proposed.

关键词： Business Mobile computing IP networks Web and internet services Companies computer networks Consumer electronics Mobile handsets Bandwidth Cellular phones

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Routing and scheduling connections in networks that support advance reservations

Routing and scheduling connections in networks that support ...

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International Conference on Broadband Networks (BroadNets)

作者： Emmanouel Varvarigos Vasileios Sourlas Konstantinos Christodoulopoulos Department of Computer Engineering and Informatics University of Patras Greece Research Academic Computer Technology Institute Patras Greece Department of Computer and Communication Engineering University of Thessally Greece

A key problem in networks that support advance reservations is the routing and time scheduling of connections with flexible starting time. In this paper we present a multicost routing and scheduling algorithm for selecting the path to be followed by such a connection and the time the data should start so as to minimize the reception time at the destination, or some other QoS requirement. The utilization profiles of the network links, the link propagation delays, and the parameters of the connection to be scheduled form the inputs to the algorithm. We initially present a scheme of non-polynomial complexity to compute a set of so-called non-dominated candidate paths, from which the optimal path can be found. By appropriately pruning the set of candidate paths using path pseudo-domination relationships, we also find multicost routing and scheduling algorithms of polynomial complexity. We examine the performance of the algorithms in the special case of an Optical Burst Switched network. Our results indicate that the proposed polynomial time algorithms have performance that it is very close to that of the optimal algorithm.

关键词： Routing Polynomials Scheduling algorithm Quality of service Processor scheduling computer networks Propagation delay Optical fiber networks informatics Protocols

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Adaptive smooth multicast protocol for multimedia data transmission

Adaptive smooth multicast protocol for multimedia data trans...

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International Symposium on Performance Evaluation of computer & Telecommunication Systems SPECTS

作者： Christos Bouras Apostolos Gkamas Georgios Kioumourtzis Research Academic Computer Technology Institute University of Patras Rion Greece Research Unit 6 Research Academic Computer Technology Institute Patras Greece Department of Telecommunications Science and Technology of Peloponnesus University of Greece Rion Greece Computer Engineering and Informatics Department University of Patras Rion Greece

ISBN: (纸本)9781424434497

We introduce Adaptive Smooth Multicast Protocol (ASMP), for multimedia transmission over best-effort networks. The smoothness lays in the calculation and adaptation of the transmission rate, which is based on dynamic estimation of protocol parameters and dynamic adjustment of the ldquosmoothness factorrdquo. ASMP key attributes are: (a) adaptive scalability to large sets of receivers, (b) TCP-friendly behavior, (c) high bandwidth utilization, and finally (d) smooth transmission rates, which are suitable for multimedia applications. We evaluate the performance of ASMP and investigate its behavior under various network conditions through extensive simulations, conducted with the network simulator software (ns2).

关键词： Multicast protocols Data communication Bandwidth Scalability Transport protocols Telecommunication computing Application software informatics Paper technology Streaming media

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