References of "Leduc, Guy"
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See detailAdaptation dynamique des débits des couches pour la transmission vidéo multipoint
Bonmariage, Nicolas; Leduc, Guy ULg

in Obaid, A. (Ed.) Ingénierie des protocoles - Réseaux mobiles et ad hoc, qualité de service, multimédia, ingénierie de trafic (2002, May 27)

The heterogeneous environment of multicast video streams naturally raises a network performance issue which can be addressed using a layered transmission scheme. A receiver is able to adapt the flow rate ... [more ▼]

The heterogeneous environment of multicast video streams naturally raises a network performance issue which can be addressed using a layered transmission scheme. A receiver is able to adapt the flow rate to its capacity by choosing an adequate subscription level among the different layers. A traditional static approach doesn't allow a full usage of the network capacity and should be combined with an adaptive transmission rate in each layer. We study the dynamic rate adaptation problem and develop a framework integrating a multirate adaptation algorithm and a transmission protocol for layered multicast video. Our main focus is the development of an adaptation algorithm offering rates matching the capacities of the receivers. We also want to set up a congestion control scheme and offer fairness towards TCP flows, while keeping a scalable framework. We evaluate and analyze the proposed architecture using simulations to point out its main characteristics. [less ▲]

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See detailComparaison quantitative de différentes techniques de restauration rapide dans les réseaux IP/MPLS
Mélon, Laurent; Leduc, Guy ULg

in Obaid, A. (Ed.) Ingénierie des protocoles - Réseaux mobiles et ad hoc, qualité de service, multimédia, ingénierie de trafic (2002, May 27)

This article is dealing with a quantitative comparison of different fast restoration approaches in the context of a Multi-Protocol Label Switching (MPLS) network. The objective is to analyse the general ... [more ▼]

This article is dealing with a quantitative comparison of different fast restoration approaches in the context of a Multi-Protocol Label Switching (MPLS) network. The objective is to analyse the general behaviour of these approaches (local rerouting, edge-to-edge rerouting, ...) in case of failure by means of simulations. This study is realised in the context of Best Effort only traffic, routing being done with a shortest paths algorithm. Many papers justify the choice between an edge-to-edge or a local scheme by means of intuition and then present a new algorithm for routing backup paths which try to optimize some parameters. Our approach aims to clarify the situation by comparing by means of concrete results the pros and cons of each mechanism. [less ▲]

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See detailA scheduler for relative delay service differentiation
Jennes, Geoffroy ULg; Leduc, Guy ULg; Tufail, Mudassir

in Annales des Télécommunications = Annals of Telecommunications (2002), 57(1-2, JAN-FEB), 83-104

We propose a new delay-based scheduler called as RD-VC (Relative Delay VirtualClock). Since it performs a delay-based service differentiation among flow aggregates, the quality at microflow level is the ... [more ▼]

We propose a new delay-based scheduler called as RD-VC (Relative Delay VirtualClock). Since it performs a delay-based service differentiation among flow aggregates, the quality at microflow level is the same as that at aggregate level. This is not easily achievable when the service differentiation is bandwidth-based or loss-based. Unlike the EDF (Earliest Deadline First) scheduler [1], our proposed scheduler self-regulates and adapts the delays according to load changes. This characteristic permits its to implement it in an AF-like PHB providing the relative quantification service in a DiffServ network. Finally, we compare our proposed RD-VC scheduler with two important existing propositions: WTP (Waiting Time Priority) [2, 3] and EX-VC (Extended VirtualClock) [4]. Both these propositions are delay-based and have self-regulation property All three schedulers (RD-VC, WTP and EX-VC) maintain the required service differentiation among aggregates and have comparable long term average performance like mean throughput per aggregate and packet loss ratio etc. However, RD-VC and WTP take an edge over EX-VC at short-term performance like jitter. Both RD-VC and WTP have good long term and short-term performance. Our proposed RD-VC, compared to existing WTP, has two additional characteristics, i.e. unlike WTP which is limited to architectures with one queue per QoS class, it has no limitation on implementation scope (with or without separate queues per class) and it has lower complexity. This renders RD-VC an interesting proposition. [less ▲]

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See detailResource Trading Agents for Adaptive Active Network Applications
Yamamoto, Lidia; Leduc, Guy ULg

in MOBILE AGENTS FOR TELECOMMUNICATION APPLICATIONS (2002)

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See detailAutonomous Reflectors over Active Networks: Towards Seamless Group Communication
Yamamoto, Lidia; Leduc, Guy ULg

in The Interdisciplinary Journal of Artificial Intelligence & the Simulation of Behavious (AISBJ) (2001), 1(1), 125-146

We present a reflector service that seeks to maintain application-level connectivity in the presence of network-level multicast failures. The service is based on the dynamic deployment of autonomous ... [more ▼]

We present a reflector service that seeks to maintain application-level connectivity in the presence of network-level multicast failures. The service is based on the dynamic deployment of autonomous reflectors modelled as mobile agents on top of an active network infrastructure. It is able to repair multicast tree failures by building a self-organising tree of reflectors, which will be connected to each other via unicast. The scheme is decentralised and takes into account node and link resources to find agent locations that lead to low cost tree configurations. We focus on the basic decision mechanisms related to code mobility during the tree construction and destruction phases, namely: cloning, migration, merging and termination. We show some preliminary simulation results that confirm the viability of the approach and settle directions for further research. [less ▲]

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See detailBuilding Bidirectional Multicast Trees Using Autonomous Reflectors
Yamamoto, Lidia; Leduc, Guy ULg

Poster (2001, October)

We show an active application to build bidirectional multicast trees, based on the dynamic deployment of agents on top of an active network infrastructure, and interconnected by unicast. Such trees are ... [more ▼]

We show an active application to build bidirectional multicast trees, based on the dynamic deployment of agents on top of an active network infrastructure, and interconnected by unicast. Such trees are used to build a repair service that seeks to maintain application-level connectivity in the presence of network-level multicast failures. Reflector trees are built on demand in a decentralized way, using three elementary agent operations: clone, migrate, and merge. They terminate automatically when no longer needed. In this paper we show how agents make decisions on which set of operations to use in order to produce a low cost tree configuration, taking node and link resources into account. [less ▲]

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See detailA Stable and Flexible TCP-friendly congestion control protocol for layered multicast transmission
El Khayat, Ibtissam; Leduc, Guy ULg

in Lecture Notes in Computer Science (2001, September 04), 2158

We propose an improvement of our RLS (Receiver-driven Layered multicast with Synchronization points) protocol, called CIFL for “Coding-Independent Fair Layered mulaticast”, along two axes. In CIFL, each ... [more ▼]

We propose an improvement of our RLS (Receiver-driven Layered multicast with Synchronization points) protocol, called CIFL for “Coding-Independent Fair Layered mulaticast”, along two axes. In CIFL, each receiver of a layered multicast transmission will try and find the adequate number of layers to subscribe to, so that the associated throughput is fair towards TCP and stable in steady-state. The first improvement is that CIFL is not specific to any coding scheme. It can work as well with an exponentially distributed set of layers (where the throughput of each layer i equals the sum of the throughputs of all layers below i), or with layers of equal throughputs, or any other scheme. The second improvement is the excellent stability of the protocol which avoids useless join attempts by learning from its unsuccessful previous attempts in the same (or better) network conditions. Moreover, the protocol tries and reaches its ideal TCP-friendly as soon as possible by computing its target throughput in a clever way when an incipient congestion is confirmed. [less ▲]

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See detailAutonomous Multicast Reflectors over Active Networks
Yamamoto, Lidia; Leduc, Guy ULg

Conference (2001, March)

We present a reflector service that seeks to maintain application-level connectivity in the presence of network-level multicast failures. The service is based on the dynamic deployment of autonomous ... [more ▼]

We present a reflector service that seeks to maintain application-level connectivity in the presence of network-level multicast failures. The service is based on the dynamic deployment of autonomous reflectors based on mobile code, on top of an active network infrastructure. It is able to repair multicast tree failures by building a self-organising tree of reflectors, which will be connected to each other via unicast. We focus on the basic decision mechanisms related to code mobility during the tree construction and destruction phases, namely: cloning, migration, merging and termination. To assist with the decisions a market-based mechanism is employed. We show some preliminary simulation results that confirm the viability of the approach and settle directions for further research. [less ▲]

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See detailIntroduction à E-LOTOS
Leduc, Guy ULg; Jeffrey, Alan; Sighireanu, Mikhaela

in Ingénierie des protocoles et qualité de service (2001)

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See detailMultimedia in the E-LOTOS Process Algebra
Leduc, Guy ULg

in Formal Methods for Distributed Processing - A Survey of Object Oriented Approaches (2001)

We illustrate how the ISO E-LOTOS language can be used to describe an ODP multicast multimedia binding object of some complexity. The timing features of the language are briefly recalled, and play a major ... [more ▼]

We illustrate how the ISO E-LOTOS language can be used to describe an ODP multicast multimedia binding object of some complexity. The timing features of the language are briefly recalled, and play a major role in the description of the example, but many other features of E-LOTOS are also very useful to obtain a more modular and more readable specification. Users familiar with LOTOS will also learn how some E-LOTOS features can advantageously replace the traditional LOTOS ones. [less ▲]

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See detailSpécification formelle des mécanismes de support des qualités de service dans l'Internet
Leduc, Guy ULg; Kuty, Ludovic

in Ingénierie des protocoles et qualité de service (2001)

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See detailInformation Technology - Enhancements to LOTOS (E-LOTOS)
Leduc, Guy ULg; et al.

Report (2001)

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See detailContrôle de congestion pour la transmission multipoint en couches
El Khayat, Ibtissam; Leduc, Guy ULg

Conference (2000, November 06)

Le contrôle de congestion en transmission multipoints est rendu difficile par l'hétérogénéité des récepteurs. En effet, pour la transmission vidéo par exemple, il serait peu raisonnable que l'émetteur ... [more ▼]

Le contrôle de congestion en transmission multipoints est rendu difficile par l'hétérogénéité des récepteurs. En effet, pour la transmission vidéo par exemple, il serait peu raisonnable que l'émetteur adapte son débit en fonction du récepteur le moins performant ou de celui qui subit temporairement la congestion la plus sévère. Pour contourner ce problème, l'émetteur peut émettre un flux structuré en couches, de telle sorte que la couche de base donne une qualité minimale et que les couches suivantes améliorent successivement cette qualité. L'algorithme de contrôle de congestion proposé est basé sur ce schéma. Il permet à chaque récepteur de sélectionner dynamiquement un sous-ensemble adéquat de couches en répondant aux objectifs suivants. Premièrement, l'algorithme doit être équitable vis-à-vis de TCP; ce qui signifie que les débits du flux multicouches reçu et celui d'un flux TCP placé dans les mêmes conditions doivent être plus ou moins les mêmes. Deuxièmement, les récepteurs doivent être suffisamment coordonnés pour qu'une congestion résultant de l'ajout d'une couche par l'un d'eux ne puisse être interprétée par un autre récepteur comme une congestion résultant de ses propres décisions ou d'un trafic perturbateur. Enfin, lorsque deux sessions multicouches empruntent un même goulet, nous souhaitons que les récepteurs obtiennent le même débit, ce qui signifiera en général des nombres de couches différents si les débits des couches sont distincts. [less ▲]

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See detailAn Active Layered Multicast Adaptation Protocol
Yamamoto, Lidia; Leduc, Guy ULg

in Lecture Notes in Computer Science (2000, October 16), 1942

We describe an active application in the field of multicast congestion control for real-time traffic. Our Active Layered Multicast Adaptation Protocol is a layered multicast congestion control scheme ... [more ▼]

We describe an active application in the field of multicast congestion control for real-time traffic. Our Active Layered Multicast Adaptation Protocol is a layered multicast congestion control scheme built on top of an Active Network infrastructure. It benefits from router support in order to obtain information about resources available and to perform the adaptation tasks at the places where shortage of resources occur. It supports heterogeneous receivers through the combination of layered multicast transmission with selective filtering and pruning of layers within the active nodes. Market-based resource management ideas are applied to achieve a resource utilisation level that represents an equilibrium between the user goals and the node operator goals. Our simulation results show that the protocol is feasible and provides adequate reactions to short term and persistent congestion, while keeping the amount of state and processing in the active nodes limited. [less ▲]

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See detailUn ordonnanceur assurant des services différenciés relatifs basés sur le délai
Jennes, Geoffroy; Leduc, Guy ULg; Tufail, Mudassir

in Courtiat, Jean-Pierre; Diaz, Michel; Sénac, Patrick (Eds.) Qualité de Service, multimédia et mobilité (2000, October)

Nous proposons l'ordonnanceur RD-VC garantissant des services différenciés (DiffServ) relativement quantifiés basés sur le délai. Un tel ordonnanceur assure que différentes classes de service obtiennent ... [more ▼]

Nous proposons l'ordonnanceur RD-VC garantissant des services différenciés (DiffServ) relativement quantifiés basés sur le délai. Un tel ordonnanceur assure que différentes classes de service obtiennent des délais inversement proportionnels à des indices de qualité fixés, quelle que soit la charge du réseau, et sans signalisation, ni contrôle d'admission. De plus, bien que cet algorithme ne s'applique qu'aux classes de services, les délais relatifs sont également respectés pour chaque flux composant ces agrégats. Ceci permet d'assurer des qualités de service au niveau des (micro)flux sans que leur grand nombre ne conduise à un effondrement du système. L'algorithme offre de bonnes performances tout en étant très peu coûteux : le traitement par paquet est très léger et il n'est même pas nécessaire de disposer d'une file d'attente par classe de service. [less ▲]

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See detailAdaptive Applications over Active Networks: Case Study on Layered Multicast
Yamamoto, Lidia; Leduc, Guy ULg

in IP Networks Versus conventional Switched Networks (2000, October)

In this paper we study the potential and limitations of active networks in the context of adaptive applications. We present a survey of active networking research applied to adaptive applications, and a ... [more ▼]

In this paper we study the potential and limitations of active networks in the context of adaptive applications. We present a survey of active networking research applied to adaptive applications, and a case study on a layered multicast active application. This active application is a congestion control protocol that selectively discards data in the active routers, and prunes multicast tree branches affected by persistent congestion. Our first results indicate that active networks can indeed help such an application to adapt to heterogeneous receivers, with a minimum amount of state overhead, equivalent to that of a single IP multicast group. [less ▲]

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See detailAn agent-inspired active network resource trading model applied to congestion control
Yamamoto, Lidia; Leduc, Guy ULg

in Lecture Notes in Computer Science (2000, September), 1931

In order to accommodate fluctuations in network conditions, adaptive applications need to obtain information about resource availability, Using active networks, new models for adaptive applications can be ... [more ▼]

In order to accommodate fluctuations in network conditions, adaptive applications need to obtain information about resource availability, Using active networks, new models for adaptive applications can be envisaged, which can benefit from the possibility to send mobile code to the network nodes. We describe a model for trading resources inside an active net-work node, based on the interaction between capsules as reactive user agents, and resource manager agents which reside in the network nodes. We apply the model to the case of a many-to-one audio application with congestion control, which trades off link resources against memory when there is congestion at the outgoing interface towards the destination. Our simulation results indicate that the application makes effective use of the available resources, and it also allows resources to be shared according to user preferences. [less ▲]

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See detailVerification of security protocols using LOTOS-method and application
Leduc, Guy ULg; Germeau, François

in Computer Communications (2000), 23(12), 1089-1103

We explain how the formal language LOTOS can be used to specify security protocols and cryptographic operations. We describe how security properties can be modelled as safety properties and how a model ... [more ▼]

We explain how the formal language LOTOS can be used to specify security protocols and cryptographic operations. We describe how security properties can be modelled as safety properties and how a model-based verification method can be used to verify the robustness of a protocol against attacks of an intruder. We illustrate our technique on a concrete registration protocol. We find an attack, correct the protocol, propose a simpler yet secure protocol, and finally a more sophisticated protocol that allows a better discrimination between intruder's attacks and classical protocol errors. (C) 2000 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailVerification of two versions of the challenge handshake authentication protocol (CHAP)
Leduc, Guy ULg

in Annales des Télécommunications = Annals of Telecommunications (2000), 55(1-2), 20-30

The challenge handshake authentication protocol, CHAP, is an authentication protocol intended for use primarily by hosts and routers that connect to a network server I in switched circuits or dial-up ... [more ▼]

The challenge handshake authentication protocol, CHAP, is an authentication protocol intended for use primarily by hosts and routers that connect to a network server I in switched circuits or dial-up lines. but might be applied to dedicated links as well. In this paper; we specify two versions of the protocol, using the formal language Lotos, and apply the Eucalyptus model-based verification tools to prove that the first version has a flaw: whereas the second one is robust to passive and active attacks. The paper is written bl a tutorial fashion with a strong emphasis oil the methodology used. The relative simplicity of the CHAP protocol allows one to include complete Lotos specifications and definitions of properties, so that the experiment can be reproduced easily. [less ▲]

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See detailCongestion Control for Layered Multicast Transmission
El Khayat, Ibtissam; Leduc, Guy ULg

in Networking and Information Systems Journal (2000), 3(3-4), 559-573

Heterogeneity of receivers makes it hard to control congestion for multicast transmission. Using hierarchical layering of the information is one of the most elegant and efficient approach to tackle this ... [more ▼]

Heterogeneity of receivers makes it hard to control congestion for multicast transmission. Using hierarchical layering of the information is one of the most elegant and efficient approach to tackle this problem. The proposed algorithm is based on this principle and has three objectives: to fulfill intra-session fairness, i.e. between different receivers of the same session; to be fair towards TCP; to fulfill inter-session fairness, i.e. same throughputs (and not number of layers) to concurrent sessions. [less ▲]

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