Open Topics

Vol. 60, n° 5-6, May-June 2005
Content available on Springerlink

Anonymous and Secure Electronic Transaction protocol

Srecko BRLEK*, Sardaouna HAMADOU**, John MULLINS***

* Laboratoire LACIM, Dép. d’Informatique, Université du Québec à Montréal
** Laboratoire CRAC, Dép. de Génie Informatique, École Polytechnique de Montréal
*** Laboratoire CRAC, Dép. de Génie Informatique, École Polytechnique de Montréal. B.P 6079, Succ. Centre-ville, Montréal (Québec), Canada, H3C 3A7

Abstract We present a new protocol for electronic transactions which is not only secure but also anonymous, the latter characteristic being obtained by associating an encryption device with a chip card. Security is ensured by the use of encryption, electronic signature and authentication. In order to check the validity of the security properties enforced by the protocol, a model and a specification are provided. The protocol modeling language is a process algebra with value passing extended by an observation mechanism allowing the specification of security levels, by cryptographic primitives, and by a function call feature on private channels allowing the modeling of interactions with the crypto-system. The anonymity is expressed by an information flow property. The verification method, based on cosimulation, is proved consistent and complete and analysis confirms that this approach ensures not only anonymity (thanks to the fact that the client never discloses to the merchant any information permitting his identification), but also the quasi-impossibility of any fraudulent transaction.

Keywords Computing transaction, Internet security, Cryptography, Integrated circuit card, Transmission protocol, e-business, Formal method, Modeling, Privacy.

Distributed mapping of the internet topology

Mickaël HOERDT, Damien MAGONI

Université Louis Pasteur – LSIIT, Boulevard Sébastien Brant, 67400 Illkirch, France

Abstract The study of the Internet topology allows us to discover properties that can be beneficial to the performances of network protocols and applications. Thus, Internet mapping is very useful to simulation software focusing on network protocols. Unfortunately Internet mapping has two major drawbacks. First it takes a lot of time to be carried out and second it is often incomplete. To solve these two problems, we have developed a fast mapping software whose aim is to map the heart of the Internet as fast as possible with the highest attainable precision. In this paper, we describe our software and evaluate its performances compared to an existing and freely available mapping software. We assess the completeness of the router level maps by creating overlays with an autonomous system topology. We also assess its use in IPv6 and the evolution of its performances in IPv4 when increasing the size of the input parameter set. We conclude with a detailed study on the delay of the paths and links in the Internet.

Keywords Internet, Cartography, Topology, Network layer, Experimental method, Comparative study, Internet protocol.

A multi-protocol and multi-service validation platform – experimentation results

Pierre COMBES1,Wei MONIN1, Ana CAVALLI2, Amel MEDERREG2, Fatiha ZAÏDI2, Richard CASTANET3, Marcien MACKAYA3, Patrice LAURENÇOT4

1. France Telecom R&D/MAP, 38-40 rue du Général Leclerc, 92130 Issy-les-Moulineaux, France.
2. GET/Institut National des Télécommunications-CNRS Samovar, 9 rue Charles Fourier, 91011 Evry cedex, France.
3. Université Bordeaux 1, Labri, Domaine Universitaire, 351 cours de la Libération, 33405 Talence cedex, France.
4. Université Blaise Pascal-Clermont II, LIMOS, Complexe scientifique des Céseaux, 63177 Aubière cedex, France.

Abstract This article presents the implementation of a validation platform based on formal methods and the experimental results obtained. This platform allows performing conformance and interoperability tests, analysing the specification and constructing a performance model for the services. It covers all stages of the validation which are : formal specification, test architecture definition, test generation and execution for the defined architecture, and performance evaluation. The test methods and architectures used here make it easier to detect and localise errors. The platform has been constructed within the framework of the RNRT (National Telecommunications Research Network) platform project, PLATONIS. This platform is composed of a network integrating the different sites of the project partners. The principal application domains for the platform are telecommunication systems and mobile telephony. In particular, two different cases study are presented that illustrate the platform’s applicability to the test of mobile 3rd generation protocols and services using WAP, GPRS and UMTS. Nevertheless, the platform is generic and can be used for other types of communication protocols and services.

Keywords Validation, Formal method, Experimental result, Transmission protocol, Telecommunication service, Performance evaluation, Mobile radiocommunication, Cellular network, Object location, Internet, Interoperability, Quality of Service, Prototype test.

IP-based transport of voice traffic in the UMTS radio access network: analytical study and empirical validation

Abedellatif SAMHAT , Tijani CHAHED, Mehdi SABEUR

GET/Institut National des Télécommunications, 9 rue Charles Fourier, 91011 Evry Cedex, France

Abstract In this paper, we investigate the IP protocol as a transport option for the user traffic in the UMTS Terrestrial Radio Access Network (UTRAN), where stringent delay bounds are to be met for both real-time and non real-time traffic. We focus on real-time voice traffic and present an analytical model for the multiplexing and transport of voice channels in the UTRAN using IP. The novelty of our model is that it analytically includes and quantifies the performance of the timer used in multiplexing arriving Frame Protocol (FP) frames into larger IP packets. We then validate our work through empirical results on a test-bed emulating the UTRAN transport functionalities. We show the trade-offs between performance, in terms of delay and link utilization, and quantify optimal values for the timer as well as the number of FP frames per IP packet for a given output link capacity.

Keywords Mobile radiocommunication, Universal Mobile Telecommunication System, Voice overIP, Access network, Analytical method, Validation, Empirical method, Multiplexing, Quality of Service, Emulator.

Expressions of the field diffracted by an inclusion

Jean-Michel L. BERNARD*, Daniel BOUCHE*, Ivan ANDRONOV**, Frédérik GUYON***

* Département de Physique Théorique et Appliquée, CEA/DIF, BP12, 91680 Bruyères le Châtel, France.
** Université de St Petersbourg, Uljanovskaja 1-1, 198904, Russie.
*** Département DEV, CEA-CESTA, 33114 Le Barp, France.

Abstract We consider the problem of the diffraction of an electromagnetic wave by a local perturbation of the characteristics of a substrate (or inclusion). The inclusion induces a diffracted field, that we define as the difference between the fields diffracted with and without it. We show that this diffracted field can be written with integrals on the volume and the surface of the inclusion. We develop in particular volume-surface integral expressions of the field, from which we deduce analytical expressions in case of low contrasts of the perturbation. We validate them by comparisons with the numerical results of a moment method.

Key words Electromagnetic wave propagation, Wave diffraction, Disturbance, Substrate, Integral representation, Theoretical study, Approximation, Numerical method.

Experimental comparison of stochastic MIMO channel models

Jean-François PARDONCHE*, Marion BERBINEAU*, Christophe SEGUINOT**

* INRETS-LEOST – 20 rue Elisée Reclus, BP 317, 59666 Villeneuve d’Ascq cedex, France
** IEMN-DHS – Cité scientifique, avenue Poincaré, BP 69, 59652 Villeneuve d’Ascq cedex, France

Abstract Performances of MIMO systems are dependant on the propagation channel properties. These properties must be correctly introduced in the MIMO channel propagation models. Several model families exist. We will particularly investigate those relying on the use of second order statistic parameters. No comparison of these models was found in a same propagation environment. As a result, this paper deals with a comparison of six different stochastic models in “indoor” and “outdoor” environments. The principle and the mathematical representation of MIMO systems are introduced. Then, we present the different models considered. The statistical parameters used in the models are computed using an experimental characterization of the two environments. The six models are then compared to measurements using the channel coefficient envelope distribution and the channel capacity. The ability of the models to express the correlation level in the channel is analysed and discussed.

Keywords Radiocommunication, Transmission channel, Stochastic model, Spatial correlation, Radio channel, Comparative study, Channel capacity, Correlation matrix, Multichannel transmission.

Robust Time-Frequency Distributions based on the robust Short Time Fourier Transform


* Elektrotehnicki fakultet Podgorica, University of Montenegro, Podgorica, Montenegro
** Nanyang Technology University, School of EEE, Block S2, Nanyang Avenue, Singapore 639798

Abstract Design of time-frequency distributions (TFDs) that are robust to the impulse noise influence is considered. The robust TFDs based on the robust short-time Fourier transform (STFT) are proposed. An efficient procedure to evaluate the robust STFT is given. Robust TFDs based on the robust STFT have better energy concentration around the signal instantaneous frequency (IF) than the robust STFT itself. Also, these TFDs are more resistant to higher impulse noise than the robust TFDs obtained using the local autocorrelation function (LAF) based minimization problem.

Keywords Signal theory, Frequency time representation, Impulsive noise, Fourier transformation, System robustness, Statistical analysis.

Study of the short pulse generation of the three quarter wave shift DFB laser (3QWS-DFB)

Abdelkarim ZATNI*, Mohamed ELHAZITI*, Abdallah RHATTOY*, Ammar SHARAIHA**, Jean LE BIHAN**

* Laboratoire d’optronique, École Supérieure de Technologie d’Agadir – B. P. 33/S, 80000 Agadir, Maroc
** Laboratoire RESO, École Nationale d’Ingénieurs de Brest, CS 73862, 29238 Brest cedex 3, France.

Abstract The purpose of this paper is to study the generation of short pulses of the three quarter wave shift distributed feedback (3QWS-DFB) laser by using switching gain technique. We have used the temporal domain model (TDM) which is a multimode spatio-temporal model that considers simultaneously all the modes of the overall intra-cavity field as well as the two following nonlinear effects, the spectral hole burning (SHB) and the gain saturation. Obtained results showed that a 3QWS-DFB laser can generate short pulses in accordance with Fourier criteria. These results show that 3QWS-DFB lasers are potential candidates as monomode optical sources for long distance high bit rate telecommunications.

Keywords Distributed feedback laser, Phase control, Ultrashort pulse, Time domain method, Non linear effect, Semiconductor laser, Large signal Behavior, Soliton, Optical source.

MPNT: a multi-protocolar broadcasting architecture

Karim SBATA, Rédouane BENAINI, Pierre VINCENT

GET/Institut National des Télécommunications, UMR SAMOVAR, Département LOR – 9 rue Charles Fourier, 91011 Evry, France

Abstract The purpose of this article is to present the MPNT architecture (Multicast Proxies NeTwork), an application level solution we developed for multicast communications. It is based on interconnected broadcasting relays for unicast or multicast standard clients. Originally conceived within the framework of TutTelNet, a distance-learning project of Enic (Télécom Lille 1), its first goal was to provide an access to distant students using any type of Internet connection. The implementation of multimedia protocols such as SIP, RTCP and RTP allowed us to extend its use to real-time applications, like heterogeneous audio-conferencing. Concerning the interconnection, the first approach was based on a spanning tree model, manually managed. Although easy-to-use and flexible, this model is limited by its possible lack of scalability. Indeed, for large-scale systems, it can be difficult to ensure an acceptable QoS. To remedy it, we introduced an alternate model, based on a hypercube topology. The main advantage of hypercube networks is their compactness : the maximal distance between two nodes increases in a logarithmic way with the number of nodes, whereas it can increase linearly (in the worst case) for spanning trees. Nevertheless, as this linear case is rare, a sharpest analyse of spanning tree performance has been done.

Key words Telecommunication network, Network architecture, Point-to-multipoint communication, Network protocol, Graph tree, Spanning tree, Interconnection, Multidimensional space.

Optimized trellis coded vector quantization of speech coder LSF parameters


Laboratoire Communication Parlée et Traitement du signal, Faculté d’Electronique et d’Informatique, Université des Sciences et de la Technologie Houri Boumediene (USTHB) – BP. 32, El-Alia, Bab-Ezzouar, Alger, 16111, Algérie

Abstract Speech coders operating at low bit rates necessitate efficient encoding of the linear predictive coding (LPC) coefficients. Line spectral Frequencies (LSF) parameters are currently one of the most efficient choices of transmission parameters for the LPC coefficients. In this paper, an optimized trellis coded vector quantization (TCVQ) scheme for encoding the LSF parameters is presented. When the selection of a proper distortion measure is the most important issue in the design and operation of the encoder, an appropriate weighted distance measure has been used during the TCVQ construction process. We further applied the optimized TCVQ system for encoding the LSF parameters of the US Federal Standard (FS1016) 4.8 kbps speech coder. At lower bit rates, objective and subjective evaluation results show that the incorporated LSF TCVQ encoder performs better than the 34 bits/frame LSF scalar quantizer used originally in the FS1016 coder. The subjective tests reveal also that the 27 bit/frame scheme produces equivalent perceptual quality to that when the LSF parameters are unquantized.

Keywords Speech coding, Signal quantization, Block quantization, Lattice coding, Optimization, Linear prediction, Spectrum line.

LDPC-based space-time coded OFDM systems: Turbo-EM receiver design with channel state information guessing algorithms

Guillaume FERRÉ, Mohamad Jamalullil SYED, Jean-Pierre CANCES, Vahid MEGHDADI, Jean-Michel DUMAS

Université de Limoges – École Nationale Supérieure d’Ingénieurs de Limoges (ENSIL), Groupe d’Étude des Systèmes de Télécommunications de l’ENSIL (UMOP/GESTE CNRS FRE 2701) – 16, Rue Atlantis, Parc ESTER, BP 6804, 87068 Limoges cedex, France.

Abstract In this paper we study some turbo receiver architectures employing low-density parity check (LDPC) codes together with orthogonal frequency division multiplexing (OFDM) for high data rate wireless transmissions. Different demodulation schemes based on expectation-maximization (EM) algorithm are studied along with the channel impulse response (CIR) algorithms. We studied different CIR guessing algorithms including the EM-based algorithms such as a space-alternating generalized expectation-maximization algorithm (SAGE). It is shown that the proposed turbo-EM receiver employing a soft maximum a posteriori (MAP) EM demodulator and a belief propagation LDPC decoder can perform within 1 dB from the ergodic capacity of the studied MIMO OFDM channels. Besides, we find that a suboptimum structure based on a soft interference cancellation MMSE filtering demodulator exhibits negligible loss in non-correlated fading MIMO channels but suffer extra performance loss in highly correlated MIMO channels.

Keywords Radiocommunication, Multichannel transmission, Space diversity, Time division multiplexing, Receiver, Demodulator, OFDM, Radio channel, Channel capacity, Learning, Impulse response, Simulation.