References of "Leduc, Guy"
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See detailEphemeral State Assisted Discovery of Peer-to-peer Networks
Martin, Sylvain ULg; Leduc, Guy ULg

in Boutaba, Raouf; Brunner, Marcus; Schmid, Stefan (Eds.) 1st IEEE Workshop on Autonomic Communications and Network Management (2007, May)

In the past few years there has been an impressive number of proposals for application-specific overlays or peerto-peer networks. However the procedure to bootstrap peers in those networks has remained an ... [more ▼]

In the past few years there has been an impressive number of proposals for application-specific overlays or peerto-peer networks. However the procedure to bootstrap peers in those networks has remained an under-researched topic, typically left as an implementation detail. In this paper, we first study the performance of history lists, a common decentralised bootstrap mechanism used in P2P applications. We then investigate how some lightweight network support, such as Ephemeral State, could help build a P2P application that would not depend on any centralised mechanism to discover other peers. [less ▲]

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See detailDelivery Guarantees In Predictable Disruption Tolerant Networks
François, Jean-Marc; Leduc, Guy ULg

in Lecture Notes in Computer Science (2007, May), 4479

This article studies disruption tolerant networks (DTNs) where each node knows the probabilistic distribution of contacts with other nodes. It proposes a framework that allows one to formalize the ... [more ▼]

This article studies disruption tolerant networks (DTNs) where each node knows the probabilistic distribution of contacts with other nodes. It proposes a framework that allows one to formalize the behaviour of such a network. It generalizes extreme cases that have been studied before where either (a) nodes only know their contact frequency with each other or (b) they have a perfect knowledge of who meets who and when. This paper then gives an example of how this framework can be used; it shows how one can find a packet forwarding algorithm optimized to meet the delay/bandwidth consumption trade-off: packets are duplicated so as to (statistically) guarantee a given delay or delivery probability, but not too much so as to reduce the bandwidth, energy, and memory consumption. [less ▲]

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See detailInferring Groups of Correlated Failures
Lepropre, Jean; Leduc, Guy ULg

Poster (2006, December)

We compare and evaluate different methods to infer groups of correlated failures. These methods try to group failure events occurring nearly simultaneously in clusters. Indeed if several failures occur ... [more ▼]

We compare and evaluate different methods to infer groups of correlated failures. These methods try to group failure events occurring nearly simultaneously in clusters. Indeed if several failures occur nearly at the same moment in a network, it is possible that these failures have the same root cause. The input data of our algorithms are IP failure notifications that can be provided by several sources. We consider two sources: IS-IS Link State Packets (LSPs) and Syslog messages. Our first results on the Abilene and GÉANT networks show that the inference methods behave differently and that using IS-IS LSPs provides more accurate results than using Syslog messages. [less ▲]

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See detailPredictable disruption tolerant networks and delivery guarantees
François, Jean-Marc; Leduc, Guy ULg

Report (2006)

This article studies disruption tolerant networks (DTNs) where each node knows the probabilistic distribution of contacts with other nodes. It proposes a framework that allows one to formalize the ... [more ▼]

This article studies disruption tolerant networks (DTNs) where each node knows the probabilistic distribution of contacts with other nodes. It proposes a framework that allows one to formalize the behaviour of such a network. It generalizes extreme cases that have been studied before where (a) either nodes only know their contact frequency with each other or (b) they have a perfect knowledge of who meets who and when. This paper then gives an example of how this framework can be used; it shows how one can find a packet forwarding algorithm optimized to meet the 'delay/bandwidth consumption' trade-off: packets are duplicated so as to (statistically) guarantee a given delay or delivery probability, but not too much so as to reduce the bandwidth, energy, and memory consumption. [less ▲]

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See detailA scalable and decentralized fast-rerouting scheme with efficient bandwidth sharing
Balon, Simon ULg; Mélon, Laurent; Leduc, Guy ULg

in Computer Networks (2006), 50(16), 3043-3063

This paper focuses on the protection of virtual circuits (Label Switched Paths, LSPs) in a (G)MPLS (Generalised Multi-Protocol Label Switching) network. The proposed algorithm is designed to protect ... [more ▼]

This paper focuses on the protection of virtual circuits (Label Switched Paths, LSPs) in a (G)MPLS (Generalised Multi-Protocol Label Switching) network. The proposed algorithm is designed to protect traffic with strong delay requirements such as EF (Expedited Forwarding) ordered aggregates in a DiffServ domain. Indeed, for this type of application, we need fast restoration in case of failure. The duplication of all the packets in a 1 + 1 end-to-end restoration scheme consumes a large amount of bandwidth. Furthermore, end-to-end recovery with bandwidth sharing schemes are usually considered to be far too slow. Local fast-rerouting is a solution which can compete with restoration times and bandwidth consumption offered by SONET self-healing rings. Our scheme includes a sophisticated resource aggregation mechanism based on the concepts of "backup-backup aggregation" and "backup-primary aggregation". The path selection algorithm is also designed to efficiently reduce the resource usage. Moreover, when considering LSPs at different preemption levels, our algorithm is able to correctly calculate the amount of bandwidth that can be preempted despite the sharing of resource. We show that our approach, though local, can compete with the state-of-the-art end-to-end recovery schemes in terms of resource consumption. The major contribution of our scheme, the "backup-primary aggregation", was then also used in the context of end-to-end recovery and improved its performance substantially. To be able to save a maximum amount of bandwidth in a decentralised implementation, the nodes that compute backup LSPs need to obtain a certain amount of link-state information. We propose a solution where the nodes learn almost all the information they need with RSVP messages. This drastically reduces the information that needs to be flooded in the whole network and is the first scalable decentralised solution capable of sharing a large amount of bandwidth. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailConception d'un protocole de contrôle de topologie pour les overlays construits sur des réseaux ad hoc
Calomme, Sandrine; Leduc, Guy ULg

in CFIP'2006 (2006, November)

Nous présentons un algorithme de création d'une structure overlay efficace pour l'inondation de messages entre un sous-ensemble donné de nœuds ad hoc. Nous exposons les similarités que ce problème ... [more ▼]

Nous présentons un algorithme de création d'une structure overlay efficace pour l'inondation de messages entre un sous-ensemble donné de nœuds ad hoc. Nous exposons les similarités que ce problème présente avec celui du contrôle de topologie et soulignons ses particularités. NBO (Neighbour-Based Overlay topology control protocol), emploie uniquement des informations faciles à obtenir : la distance, exprimée en hops, entre chaque paire de nœuds et leur identifiant. Nous avons estimé la qualité de la structure obtenue sur base de la bande passante consommée par inondation, de la charge des nœuds overlay lors d'une inondation, et du temps nécessaire à la réception d'un message par tous les membres de l'overlay. NBO est plus performant que le meilleur protocole de contrôle de topologie overlay homogène possible. [less ▲]

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See detailPrédiction de mobilité par le mobile ou par le point d'accès: comparaison sur base de traces réelles
François, Jean-Marc; Leduc, Guy ULg

in CFIP'2006 (2006, November)

Le problème de la prédiction de mobilité se définit comme le fait de deviner quel sera le prochain point d'accès rencontré par un terminal mobile lors de son déplacement dans un réseau sans fil. Les ... [more ▼]

Le problème de la prédiction de mobilité se définit comme le fait de deviner quel sera le prochain point d'accès rencontré par un terminal mobile lors de son déplacement dans un réseau sans fil. Les prédictions faites permettent d'améliorer la qualité de service fournie par le réseau en lui permettant de prendre des mesures pro-actives (telles des réservations de ressources). Les agents de prédiction se classent principalement en deux catégories: les agents liés à un mobile particulier (responsables d'anticiper les déplacements de celui-ci) et ceux liés à un point d'accès (prédisant le prochain point d'attache de tous les terminaux y étant connectés). Cet article vise à comparer les deux méthodes à l'aide de traces réelles tirées d'un réseau WiFi de grande taille. Il montre que certains postulats souvent admis (comme le fait que les habitudes de mouvement du week-end sont différentes de celles du reste de la semaine) doivent être revus. [less ▲]

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See detailAutonomic Networking
Gaiti, Dominique; Pujolle, Guy; Al-Shaer, Ehab et al

Book published by Springer (2006)

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See detailA scalable heuristic for hybrid IGP/MPLS traffic engineering - Case study on an operational network
Skivée, Fabian; Balon, Simon ULg; Leduc, Guy ULg

in 14th IEEE International Conference on Networks (2006, September)

In current IP networks, a classical way to achieve traffic engineering is to optimise the link metrics. This operation cannot be done too often and can affect the route of a lot of traffic. Multiprotocol ... [more ▼]

In current IP networks, a classical way to achieve traffic engineering is to optimise the link metrics. This operation cannot be done too often and can affect the route of a lot of traffic. Multiprotocol Label Switching (MPLS) opens new possibilities to address the limitations of IP systems concerning traffic engineering thanks to explicit label-switched paths (LSPs). This paper proposes a new method based on simulated annealing meta-heuristic to compute a set of LSPs that optimise a given operational objective. The hybrid IGP/MPLS approach takes advantage of both IP and MPLS technologies and provides a flexible method to traffic engineer a network on a day to day basis. We illustrate the capabilities of our method with some simulations and a comparison with other techniques on an existing operational network. The results obtained by setting up a small number of LSPs are nearly optimal and better than by engineering the IGP weights. Moreover, although it could be combined with a static setting of the latter, SAMTE alone gives already the same results as this combination in much less CPU time, which thus allows an administrator to keep its initial and meaningful IGP metrics in his network. [less ▲]

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See detailDividing the Traffic Matrix to Approach Optimal Traffic Engineering
Balon, Simon ULg; Leduc, Guy ULg

in 14th IEEE International Conference on Networks (2006, September)

In this paper we propose a new method to approach optimal Traffic Engineering routing. The method consists of dividing the traffic matrix into $N$ sub-matrices, called strata, and route each of these ... [more ▼]

In this paper we propose a new method to approach optimal Traffic Engineering routing. The method consists of dividing the traffic matrix into $N$ sub-matrices, called strata, and route each of these independently. We propose two different implementations of our method in routers. Our method can also be used to compute a very precise approximation of the optimal value of a given objective function for comparison to heuristic Traffic Engineering algorithms. For this application, our algorithm is very efficient on large topologies compared to an LP formulation. [less ▲]

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See detailMultiple Description Coding versus Transport Layer FEC for Resilient Video Transmission
Soldani, Cyril ULg; Verdicchio, Fabio; Leduc, Guy ULg et al

(2006, August)

Video content delivery is a challenging task due to its large bandwidth requirements and its sensitivity to transmission errors. In this context, simultaneously providing scalability and resilience ... [more ▼]

Video content delivery is a challenging task due to its large bandwidth requirements and its sensitivity to transmission errors. In this context, simultaneously providing scalability and resilience against transmission errors is of paramount importance. Layered video coding coupled with multicast video transmission employing no feedback provides the required scalability features and reduces the network burden. However, it is not easy to provide reliability in such environments. This is crucial to mobile users as error rates on wireless links can be high. To compensate for transmission errors, redundancy must be added to the video content. This can be added at the application layer by the employed video coding system, or can be added transparently by the transport layer. In this paper, we compare the performance obtained with a scalable wavelet-based video codec that adds redundancy using multiple description coding with the equivalent system adding redundancy at the transport level, using forward error correction. [less ▲]

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See detailHow well do traffic engineering objective functions meet TE requirements?
Balon, Simon ULg; Skivée, Fabian ULg; Leduc, Guy ULg

in Lecture Notes in Computer Science (2006, May), 3976

We compare and evaluate how well-known and novel networkwide objective functions for Traffic Engineering (TE) algorithms fulfil TE requirements. To compare the objective functions we model the TE problem ... [more ▼]

We compare and evaluate how well-known and novel networkwide objective functions for Traffic Engineering (TE) algorithms fulfil TE requirements. To compare the objective functions we model the TE problem as a linear program and solve it to optimality, thus finding for each objective function the best possible target of any heuristic TE algorithm. We show that all the objective functions are not equivalent and some are far better than others. Considering the preferences a network operator may have, we show which objective functions are adequate or not. [less ▲]

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See detailOn the accuracy of analytical models of TCP throughput
El Khayat, Ibtissam; Geurts, Pierre ULg; Leduc, Guy ULg

in Lecture Notes in Computer Science (2006, May), 3976

Based on a large set of TCP sessions we first study the accuracy of two well-known analytical models (SQRT and PFTK) of the TCP average rate. This study shows that these models are far from being accurate ... [more ▼]

Based on a large set of TCP sessions we first study the accuracy of two well-known analytical models (SQRT and PFTK) of the TCP average rate. This study shows that these models are far from being accurate on average. Actually, our simulations show that 70% of their predictions exceed the boundaries of TCP-Friendliness, thus questioning their use in the design of new TCP-Friendly transport protocols. Our study also shows that the inaccuracy of the PFTK model is largely due to its inability to make the distinction between the two packet loss detection methods used by TCP: triple duplicate acknowledgments or timeout expirations. We then use supervised learning techniques to infer models of the TCP rate. These models show important accuracy improvements when they take into account the two types of losses. This suggests that analytical model of TCP throughput should certainly benefit from the incorporation of the timeout loss rate. [less ▲]

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See detailNeighbour-Based Overlay Topology Control in Ad Hoc Networks
Calomme, Sandrine; Leduc, Guy ULg

Poster (2006, May)

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See detailTOTEM: A Toolbox for Traffic Engineering Methods
Lepropre, Jean; Balon, Simon ULg; Leduc, Guy ULg

Poster (2006, April)

In this document, we propose a demonstration of TOTEM, a TOolbox for Traffic Engineering Methods. This toolbox integrates a series of tools for intra-domain and inter-domain traffic engineering of IP and ... [more ▼]

In this document, we propose a demonstration of TOTEM, a TOolbox for Traffic Engineering Methods. This toolbox integrates a series of tools for intra-domain and inter-domain traffic engineering of IP and MPLS networks. It provides an open source software that allows an operator to test methods coming from the academic research. A researcher can also use the toolbox to compare and promote new TE algorithms. The toolbox is designed to be deployed either as an on-line tool in an operational network, or as an off-line traffic engineering simulator. [less ▲]

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See detailAn open source traffic engineering toolbox
Leduc, Guy ULg; Abrahamsson, Henrik; Balon, Simon ULg et al

in Computer Communications (2006), 29(5), 593-610

We present the TOTEM open source Traffic Engineering (TE) toolbox and a set of TE methods that we have designed and/or integrated. These methods cover intra-domain and inter-domain TE, IP-based and MPLS ... [more ▼]

We present the TOTEM open source Traffic Engineering (TE) toolbox and a set of TE methods that we have designed and/or integrated. These methods cover intra-domain and inter-domain TE, IP-based and MPLS-based TE. They are suitable for network optimisation, better routing of traffic for providing QoS, load balancing, protection and restoration in case of failure, etc. The toolbox is designed to be deployed as an on-line tool in an operational network, or used off-line as an optimisation tool or as a traffic engineering simulator. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailA survey of optimal network congestion control for unicast and multicast transmission
Bonmariage, Nicolas; Leduc, Guy ULg

in Computer Networks (2006), 50(3), 448-468

In the last few years, there has been a large body of literature on congestion control based on optimization and control theories. This paper provides an overview of optimization flow control starting ... [more ▼]

In the last few years, there has been a large body of literature on congestion control based on optimization and control theories. This paper provides an overview of optimization flow control starting from the first original papers, and traces the development in a unified framework, from unicast to multicast, from theory to algorithms to implementation issues. The optimal congestion control problem is formulated, both for unicast and multicast. Decentralized theoretical solutions are derived by applying duality theory. Based on these results, actual generic algorithms and implementations are proposed for solving these problems in a distributed way. Some alternative methods not based on duality theory are also reviewed. Finally the complementary problem of choosing suitable utility functions in the optimization problem is addressed. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailForeword - Transport protocols for next generation networks
Pham, Congduc; Leduc, Guy ULg

in Annales des Télécommunications = Annals of Telecommunications (2006), 61(1-2, JAN-FEB), 2-4

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See detailThe Critical Neighbourhood Range for Asymptotic Overlay Connectivity in Ad Hoc Networks
Calomme, Sandrine; Leduc, Guy ULg

in Ad Hoc & Sensor Wireless Networks (2006), 2(2), 169-187

We first motivate the use of ad hoc overlays. In particular, we argue that overlay routing could play a role in the spreading of ad hoc networks. We then define a simple criterion for neighbourhood: two ... [more ▼]

We first motivate the use of ad hoc overlays. In particular, we argue that overlay routing could play a role in the spreading of ad hoc networks. We then define a simple criterion for neighbourhood: two overlay nodes are neighbours if and only if there exists a path between them of at most R hops, and R is called the (overlay) neighbourhood range. A small R may result in a disconnected overlay, while an unnecessarily large R would generate extra control traffic. We are interested in the minimum R ensuring overlay connectivity, the so-called critical R. We study conditions on R to achieve asymptotic connectivity of the overlay almost surely, i.e. connectivity with probability 1 when the number of nodes in the underlying ad hoc network tends to infinity (so-called dense networks) or when the size of the field tends to infinity (socalled sparse networks), under the hypothesis that the underlying ad hoc network is itself asymptotically almost surely connected. For dense networks, we derive a necessary and sufficient condition on R, and for sparse networks we derive distinct necessary and sufficient conditions that are however asymptotically tight. These conditions, though asymptotic, shed some light on the relation linking the critical R to the number of nodes n, the field size the radio transmission range r and the overlay density D (i.e., the proportion of overlay nodes). These conditions can be considered as approximations when the number of nodes (resp. the field) is large enough. Since r is considered as a function of n or l , we are able to study the impact of topology control mechanisms, by showing how the shape of this function impacts the critical R. [less ▲]

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See detailEntropy-based knowledge spreading and application to mobility prediction
François, Jean-Marc; Leduc, Guy ULg

in ACM International conference on Emerging Network Experiments and Technologies (2005, October)

The low quality of service provided by wireless networks does not facilitate the setup of long-awaited services, such as video conversations. In a cellular network, handoffs are an important cause of ... [more ▼]

The low quality of service provided by wireless networks does not facilitate the setup of long-awaited services, such as video conversations. In a cellular network, handoffs are an important cause of packet losses and delay jitter. These problems can be mitigated if proactive measures are taken. This requires each cell to guess the next handoff of each mobile terminal, a problem known as mobility prediction. This prediction can occur thanks to some clues (such as signal strength measurements) giving information about the terminals motion. For example, a clue that locates on which road a mobile is moving is likely to be interesting for all the prediction-enabled cells along that road ---and should therefore be sent to them. This paper proposes a new method aimed at selecting the most relevant clues and finding where to propagate those clues so as to optimize mobility predictions. The pertinence of a clue is measured using information theory and by means of decision trees. This pertinence estimation is exchanged between the cells and allows to build a"relevance map" that helps determine where clues should be sent. It is adapted to the characteristics of wireless terminals such as low bandwidth and processing power. [less ▲]

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