Open Topics

Vol. 60, n° 9-10, September-October 2005
Content available on Springerlink

The structure of international Internet hyperlinks and bilateral bandwidth

George A. BARNETT*, Han Woo PARK**

* Department of Communication, School of Informatics, State University of New York at Buffalo – Buffalo, NY 14260-1060, USA
** Department of Communication & Information, YeungNam University – Gyeong San, South Korea

Abstract Using network analysis, this article examines the structure of the international Internet as a global communication system. The number of inter-domain hyperlinks embedded in web-sites for 47 nations were gathered using Alta Vista. Data were also obtained on the bandwidth connections among 63 nations. The results indicate that the U.S. is most central nation in the hyperlink network, followed by the Australia, U.K., China and Japan. Most peripheral are Uruguay, Luxemburg, UAE., and Thailand. A cluster analysis found a single group centered about the U.S. The analysis of the bandwidth network revealed that the U.S. is the most central nation, followed by the U.K., Germany, Hong Kong, Singapore and Japan. Most peripheral are Iceland, Lithuania, and Morocco. This network had three groupings, 1) the English-speaking countries with Scandinavia, Belgium, The Netherlands, and East Asia, 2) South America, and 3) Franco-German Europe. The correlation between the two networks indicates that the physical infrastructure is an important determinant of hyperlink communication. However, it is not the only determinant, others may be cultural or linguistic. The results are discussed in terms of world system theory, the evolution of Internet and globalization.

Keywords Internet, Internationalization, International network, Hypermedia, World Wide Web, Statistical analysis, Social aspect.

Reactive congestion control algorithm in an ATM node

Abdelmalek DADA*, Abdelhak BENNIA**

* Direction des transmissions nationales, BP 250 Constantine RP, 25 000 Constantine, Algérie
** Département d’électronique, Faculté des sciences de l’ingénieur, Campus de Zerzarra, Université de Constantine, 25 000 Constantine, Algérie.

Abstract This paper discusses the congestion phenomenon on an ATM node and presents an analytical approach to follow the cumulated delays on the network. It proposes an adaptation algorithm of the sources rate with the evolving congestion state of a node by a reactive approach.

Keywords: ATM, Congestion control, Resource management, Telecommunication network, Adaptive method.

A tabu heuristic for routing and wavelength assignment with failure scenarios

Christiane DZONGANG*, Philippe GALINIER*, Samuel PIERRE*

* Département de génie informatique – École Polytechnique de Montréal, C.P. 6079, succ. Centre-ville, Montréal, Québec, Canada H3C 3A7

Abstract This paper proposes a heuristic approach to solve the optical routing problem with wavelength continuity constraint. For each single link failure in the network and for a number of wavelengths available on each optical link, the goal is to maximize the number of routed connections. The routing is based on the search for the shortest paths whereas the wavelength assignment is based on a graph coloring method using tabu search. Two versions of this approach have been implemented and extensive experiments have been carried out for performance evaluation purposes, by focusing on the blocking rate and the execution times. As a result, it has been observed that the fact of raising the number of wavelengths decreases the blocking rate.

Key words: Optical telecommunication, Network routing, Wavelength division multiplexing, Heuristic method, Graph coloration, Blocking, Failure, Graph path.

Tunable optical coupler


* École Nationale Supérieure Polytechnique, Université Marien Ngouabi – B. P. 69 Brazzaville, Congo

Abstract Two prototypes of 1 x 2 tunable couplers were produced starting from polymeric fibres (of diameter 1 mm) and of silica fibres (200/300 mm). They have an input and two output ports, all located in the same bisecting plan. An optics with mobile prism makes it possible to tune the power splitting ratios between the two output ports. The performances of these couplers in terms of power splitting ratios between the two output ports were evaluated with the wavelengths of 633 nm and 850 nm. Experiments show large tuning ranges. Such couplers are needed to optimize ON-OFF ratios in interferometric devices.

Keywords Optical coupler, Tunable circuit, Power divider, Optical fiber.

Characterization of electromagnetic emission due to power line communication (PLC) networks

Lamine KONÉ*, Richard RAZAFFERSON*, Bernard DÉMOULIN*, Fabienne MOULIN**, Frédéric GAUTHIER**, Ahmed ZEDDAM**

* IEMN-DHS – Groupe TELICE, USTL, Université des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq Cedex, France.
** France Telecom R&D, 2, avenue P. Marzin 22307 Lannion Cedex, France.

Abstract Use of Power Lines Communication for purpose such as Internet access or in-home applications seems to be a very attractive way, however, the problem of conducted and radia- ted electromagnetic emissions due to these new systems is quite set. The risk of disturbing the Radio communications is, at all, critical in the so-called Short Waves band, from 1 MHz to 30 MHz, allowed to PLC. This paper is aimed in analysing the phenomena that rise to these radiated electromagnetic emissions. We focus especially the analysis to the characterisation of magnetic field by means of simple physical concepts. The experimental and theoretical investigations involve usual power lines owning different dimension and complexity. A large part of this paper is devoted to physical interpretations of the measurement results, underlining the correlation between the magnetic field emission and the common and differential modes currents driven through the line, as well as the connection with the geometrical parameters of the line and with the connected loads. Finally, we present an approach that allows the assessment of the power deliverable by PLC. devices in accordance with the requirements of the harmonised standard EN55022 dealing with conducted emission on the power network.

Keywords Electric distribution network, Power line communication, Electromagnetic disturbance, Common mode, Differential mode, Magnetic field, Monopole antenna, Electromagnetic compatibility, High rate, Standards.

Iterative correction of phase noise and nonlinear distortion in orthogonal frequency division multiplexing (OFDM) systems

François MARX*, Joumana FARAH**, Clovis FRANCIS***

* France Telecom, Research and Development – 28, chemin du Vieux Chêne, 38240 Meylan, France.
** Faculty of Sciences & Computer Engineering, Holy-Spirit University of Kaslik, P.O. Box 446 Jounieh, Lebanon.
*** Faculty of Engineering, Lebanese University, Beirut, Lebanon.

Abstract In this paper, we present an iterative approach for the cancellation of phase errors induced by local oscillators in an OFDM receiver as well as the distortion resulting from nonlinear amplifiers. We investigate the influence of several parameters on the system performances, such as the modulation scheme, the number of carriers and the clipping ratio. Simulation results prove the effectiveness of the proposed algorithm for the cancellation of phase errors and non-linear distortion. We show that an error floor occurs for high values of the phase noise or the clipping ratio. This effect can be alleviated using an appropriate channel coding scheme, in conjunction with our iterative algorithm, for the correction of residual errors. We also show that the proposed algorithm complexity is nearly a linear function of the number of sub-carriers.

Keywords OFDM, Phase modulation noise, Non linear distortion, Iteration, Algorithm complexity, Error correction, Error correcting code.

A simple computer program for microwave radio link performance analysis

Memduh CAN*,**, A. Hamit SERBEST*

* Dept. of Electrical and Electronics Eng., Çukurova Univ., 01330 Balcali, Adana, Turkey.
** Telsim Mobile Telecommunications, Medyapark, No: 118, Yuregir, Adana, Turkey.

Abstract A simple computer program is developed for system power budget analysis of microwave radio links. As known, such an analysis is very important in radio link network planning and optimization of the existing transmission networks. The performance of the program developed in this study is tested by applying it to Adana region and by comparing with measurement results.

Keywords Radiocommunication, Microwave, System performance, Numerical simulation, Power budget, Computer program.

Indoor environments propagation simulation using a hybrid MoM and UTD electromagnetic method

Stelios A. MITILINEOS, Stylianos C. PANAGIOTOU, Pantelis K. VARLAMOS, Christos N. CAPSALIS

National Technical University of Athens-NTUA, School of Electrical and Computer Engineering, Division of Information Transmission Systems and Material Technology – Iroon Polytechniou, 9, 157 73 Athens, Greece

Abstract Radio channel observation and characterization is indispensable in mobile communications systems development. Efficient propagation prediction is crucial for rapid and costeffective systems deployment. On-site measurements, statistical models, propagation prediction and deterministic modeling are widely used for the qualification of radio channels. In this paper, a simulation tool for deterministic channel modeling in indoor environments is evolved. A hybrid combination of the Method-Of-Moments (MoM) and the Uniform Theory of Diffraction (UTD) is used. Statistical characteristics of a simple office room are calculated and the results are in excellent agreement with corresponding results of relative research on the field.

Keywords Electromagnetic wave propagation, Radio wave, Indoor radiocommunication, Numerical simulation, Moment method, Wave diffraction, Deterministic model, Hybrid model.

Modelisation and time-frequency analysis of reflected signals obtained for a guided transmission line in a stratified medium

Jamal BELKADID*, Saad Dosse BENNANI**, Mounir RIFI***

* LASSI, École Nationale des Sciences Appliquées, BP.33/S, Agadir – Maroc
** LT, École Nationale des Sciences Appliquées, BP 696, Oujda – Maroc
*** École Supérieure de Technologie, BP. 8012 Oasis, Rte d’El Jadida Casablanca – Maroc

Abstract We present in this paper a discrete temporal approach leading us to model the propagation of a signal ultra high frequency in a laminated medium. This stage will lead to a digital model calculating, starting from the equations of the lines of transmission whose parameters are adapted according to the propagation medium, the temporal shape of the reflected signal such as it is recorded by a reflectometer. A time-frequency analysis of the reflected signal allows, by varying the value of a threshold on the scallogramme of the signal, to detect a lossy thin zone which do not appear in the first results. the value of the threshold depends on the degree of attenuation of this zone.

Keywords Geophysical prospecting, Radar, Transmission line, Wave reflection, Ground, Frequency time representation, Electrical characteristic, Electromagnetic wave propagation, Guided wave, Humidity, Microwave reflectometer, Time domain method, Stratified medium, Waveguide, Wavelets.

Service Level Agreement in optical networks

Michel DU-POND1,4, Olivier AUDOUIN3, Bela BERDE3, Belkacem DAHEB1,4, Wissam FAWAZ2,4, Guy PUJOLLE1, Martin VIGOUREUX3

(1) LIP6, Université Pierre et Marie Curie, 8 rue du Capitaine Scott, 75015 Paris, France.
(2) Université Paris 13, L2TI – 99 av. Jean-Baptiste Clément, 93 430 Villetaneuse, France.
(3) Alcatel CIT, route de Nozay, 91 460 Marcoussis, France.
(4) Institut Supérieur d’Electronique de Paris (ISEP) – 28, rue Notre-Dame des Champs, 75006 Paris, France

Abstract This article proposes a Service Level Agreement applied to the optical domain (O-SLA), which is expected to be the near and long term network technology thanks, among other things, to the great bandwidth capacity offered by optical devices. After an exposition of the rationale behind an optical SLA, parameters which could enter in this O-SLA, as well as their values for four classes of services, are proposed. Different client (wavelength or sub-wavelength) and services types (from leased wavelength to bandwidth on demand) are distinguished when necessary.

Keywords Telecommunication network, Optical telecommunication, Traffic contract, Quality of Service, Technical specification.