References of "Leduc, Guy"
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See detailComparing traffic engineering objective functions
Balon, Simon ULg; Skivée, Fabian; Leduc, Guy ULg

in CoNext 2005 - Student Workshop (2005, October)

We compare and evaluate how well-known and novel network-wide 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 network-wide 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. Our first results suggest that they can give quite different results. [less ▲]

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

in Challenges in Ad Hoc Networking (2005, June)

We define, for an overlay built on top of an ad hoc network, 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 ... [more ▼]

We define, for an overlay built on top of an ad hoc network, 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 derive a necessary and sufficient condition on R to achieve asymptotic connectivity of the overlay almost surely, i.e. connectivity with probability 1 when the number of overlay nodes tends to infinity, under the hypothesis that the underlying ad hoc network is itself asymptotically almost surely connected. This condition, though asymptotic, sheds some light on the relation linking the critical R to the number of nodes n, the normalized radio transmission range r and the overlay density D (i.e., the proportion of overlay nodes). This condition can be considered as an approximation when the number of nodes is large enough. Since r is considered as a function of n, 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 detailAn active platform as middleware for services and communities discovery
Martin, Sylvain ULg; Leduc, Guy ULg

in Lecture Notes in Computer Science (2005, May), 3516

In an increasing number of cases, network hosts need to locate a machine based on its role in a service or community rather than based on a well-known address. We propose and evaluate WASP, a lightweight ... [more ▼]

In an increasing number of cases, network hosts need to locate a machine based on its role in a service or community rather than based on a well-known address. We propose and evaluate WASP, a lightweight active platform where ephemeral state left in the network can help locate service providers such as request dispatchers or computation aggregators. In an active grid architecture, WASP can also help locate participants, build and manage overlays. [less ▲]

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See detailImproving TCP in wireless networks with an adaptive machine-learnt classifier of packet loss causes
El Khayat, Ibtissam; Geurts, Pierre ULg; Leduc, Guy ULg

in Lecture Notes in Computer Science (2005, May), 3462

TCP understands all packet losses as buffer overflows and reacts to such congestions by reducing its rate. In hybrid wired/wireless networks where a non negligible number of packet losses are due to link ... [more ▼]

TCP understands all packet losses as buffer overflows and reacts to such congestions by reducing its rate. In hybrid wired/wireless networks where a non negligible number of packet losses are due to link errors, TCP is unable to sustain a reasonable rate. In this paper, we propose to extend TCP Newreno with a packet loss classifier built by a supervised learning algorithm called 'decision tree boosting'. The learning set of the classifier is a database of 25,000 packet loss events in a thousand of random topologies. Since a limited percentage of wrong classifications of congestions as link errors is allowed to preserve TCP-Friendliness, our protocol computes this constraint dynamically and tunes a parameter of the classifier accordingly to maximise the TCP rate. Our classifier outperforms the Veno and Westwood classifiers by achieving a higher rate in wireless networks while remaining TCP-Friendly. [less ▲]

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See detailMobility prediction's influence on QoS in wireless networks: a study on a call admission algorithm
François, Jean-Marc; Leduc, Guy ULg

(2005, April)

Several mechanisms increase the QoS level of mobile networks thanks to an underlying mobility prediction method (i.e. a means to predict a mobile's next access router). This paper aims at studying how the ... [more ▼]

Several mechanisms increase the QoS level of mobile networks thanks to an underlying mobility prediction method (i.e. a means to predict a mobile's next access router). This paper aims at studying how the accuracy of the prediction method can influence the network QoS in the particular context of call admission control. It shows that (a) the mobiles behaviour must be adapted according to the prediction scheme accuracy in order to achieve good performance and (b) the admission algorithm can be modified to increase its fairness and to give mobiles an incentive to do such an adaptation. [less ▲]

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See detailArchitecture d'une boîte à outils d'algorithmes d'ingénierie de trafic et application au réseau GEANT
Skivée, Fabian; Balon, Simon ULg; Delcourt, Olivier et al

in Ingénierie des protocoles - Qualité de service, multimédia et mobilité (2005, March)

This paper presents the software architecture of a traffic engineering toolbox. The methods already included cover MPLS-based intra-domain traffic engineering (TE), but will soon cover IP-based TE and ... [more ▼]

This paper presents the software architecture of a traffic engineering toolbox. The methods already included cover MPLS-based intra-domain traffic engineering (TE), but will soon cover IP-based TE and inter-domain TE. This toolbox provides an open source software that allows an operator to test methods coming from the academic research. A researcher can also use the toolbox for comparing and promoting his/her TE algorithms. The toolbox is designed to be deployed as an on-line tool in a operational network or as a traffic engineering simulator. We present a case study of traffic optimisation on the GÉANT network that compares different routing algorithms, evaluates different protection cost, and analyses the worst-case link failure. [less ▲]

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See detailA Machine Learning Approach to Improve Congestion Control over Wireless Computer Networks
Geurts, Pierre ULg; El Khayat, Ibtissam; Leduc, Guy ULg

(2004, November)

In this paper, we present the application of machine learning techniques to the improvement of the congestion control of TCP in wired/wireless networks. TCP is suboptimal in hybrid wired/wireless networks ... [more ▼]

In this paper, we present the application of machine learning techniques to the improvement of the congestion control of TCP in wired/wireless networks. TCP is suboptimal in hybrid wired/wireless networks because it reacts in the same way to losses due to congestion and losses due to link errors. We thus propose to use machine learning techniques to build automatically a loss classifier from a database obtained by simulations of random network topologies. Several machine learning algorithms are compared for this task and the best method for this application turns out to be decision tree boosting. It outperforms ad hoc classifiers proposed in the networking literature. [less ▲]

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See detailA distributed algorithm for weighted max-min fairness in MPLS networks
Skivée, Fabian ULg; Leduc, Guy ULg

in Lecture Notes in Computer Science (2004, August), 3124

We propose a novel distributed algorithm to achieve a weighted max-min sharing of the network capacity. We present the Weight Proportional Max-Min policy (WPMM) that supports a minimal rate requirement ... [more ▼]

We propose a novel distributed algorithm to achieve a weighted max-min sharing of the network capacity. We present the Weight Proportional Max-Min policy (WPMM) that supports a minimal rate requirement and an optional maximal rate constraint and allocates network bandwidth among all aggregates based on a weight associated with each one. Our algorithm achieves this policy for IP/MPLS networks using the RSVP-TE signalling protocol. It uses per-LSP accounting in each node to keep track of the state information of each LSP. It uses a novel explicit bottleneck link strategy and a different control architecture in which we update the control packet in the forward path. Simulations show that these two elements improve substantially the convergence time compared to algorithms designed for ATM networks. [less ▲]

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See detailTCP Vegas-like algorithm for layered multicast transmission
Ait-Hellal, Omar; Leduc, Guy ULg

in Communications in Computing (2004, June)

Layered multicast is probably the most elegant solution to tackle the heterogeneity problem in multicast delivery of real-time multimedia streams. However, the multiple join experiments carried out by ... [more ▼]

Layered multicast is probably the most elegant solution to tackle the heterogeneity problem in multicast delivery of real-time multimedia streams. However, the multiple join experiments carried out by different receivers in order to detect the available bandwidth make it hard to achieve fairness. In the present paper, we present a simple protocol, inspired from TCP-Vegas, that reduces considerably the unnecessary join experiments while achieving intra-session and inter-session fairness as well as being TCP-Friendly. [less ▲]

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See detailPerformance Study of an Overlay Approach to Active Routing in Ad Hoc Networks
Calomme, Sandrine; Leduc, Guy ULg

(2004, June)

We motivate the use of the active technology for routing in ad hoc networks. We present an active architecture where passive and active nodes can operate together, avoiding any change in the legacy muti ... [more ▼]

We motivate the use of the active technology for routing in ad hoc networks. We present an active architecture where passive and active nodes can operate together, avoiding any change in the legacy muti-hop routing protocol they use. We detail a basic reactive protocol which can be used to build any overlay on top of an ad hoc network. We model it as an active application called Re-Active Routing (RAR). RAR provides dynamic routing in dense and sparse active overlays. We investigate its performance in static and dynamic environments and show that it depends substantially on the active range, i.e. on the allowed maximal number of hops between two active nodes. For a well-chosen active range, RAR achieves good performance even if the mobility level is high and the overlay density is as low as 12.5 %. [less ▲]

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See detailLearning movement patterns in mobile networks: a generic method
François, Jean-Marc; Leduc, Guy ULg; Martin, Sylvain ULg

in European Wireless 2004 (2004, February)

Predicting terminals movements in mobile networks is useful for more than one reason, in particular for routing management. A way to do such prediction is to learn the movement patterns of mobile nodes ... [more ▼]

Predicting terminals movements in mobile networks is useful for more than one reason, in particular for routing management. A way to do such prediction is to learn the movement patterns of mobile nodes passing by an access router. In this paper, the information (e.g. layer 2 measurements) related to the different paths followed by mobiles are learned using a hidden Markov model. Simulations have been done using this method and show it can handle different layer~2 signals and collect statistical information when no such signal is available. Furthermore, the method works when no information is available and can be extended so as to guess the timing of the handoffs. [less ▲]

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See detailA dynamic neighbourhood discovery protocol for active overlay networks
Martin, Sylvain ULg; Leduc, Guy ULg

in Lecture Notes in Computer Science (2004), 2982

d-RADAR(1) is a neighbourhood discovery protocol for overlay network environments designed for (but not limited to) active network overlays. The core of the algorithm is an expanding ring-search based on ... [more ▼]

d-RADAR(1) is a neighbourhood discovery protocol for overlay network environments designed for (but not limited to) active network overlays. The core of the algorithm is an expanding ring-search based on the IP routing table content augmented with traffic-based and dynamic refreshing techniques that allows it to react to virtual topology changes (nodes joining/leaving the overlay) as well as IP topology changes (broken and repaired link, route changes and moving nodes). This paper presents how the protocol detects overlay candidate nodes using probing capsules and the algorithms needed to select neighbours among the candidates. We also show how d-RADAR keeps the neighbouring table up to date and learns topology changes while keeping a low discovery and refresh overhead. A short summary of simulations carried out with our active network simulator illustrates how these algorithms actually behave. [less ▲]

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See detailEvaluation d'une méthode de prédiction des déplacements de terminaux dans les réseaux mobiles
François, Jean-Marc; Leduc, Guy ULg; Martin, Sylvain ULg

in Ingénierie des protocoles - Réseaux mobiles et ad hoc, qualité de service, test et validation (2003, October)

Dans les réseaux mobiles, la prédiction du déplacement des terminaux fait régulièrement l'objet d'études: c'est une étape importante sur le chemin des garanties de QoS dans ces réseaux. Dans les ... [more ▼]

Dans les réseaux mobiles, la prédiction du déplacement des terminaux fait régulièrement l'objet d'études: c'est une étape importante sur le chemin des garanties de QoS dans ces réseaux. Dans les infrastructures actuelles, les sources d'informations permettant d'induire le déplacement d'un mobile sont multiples; de plus, le cas des terminaux incapables d'émettre de telles informations est aussi fréquent qu'important. Dans ces conditions, pour qu'un mécanisme de prédiction puisse se déployer, il lui faut pouvoir s'adapter à cette diversité de façon flexible. L'évaluation d'un tel mécanisme est le sujet de cet article; il s'agit d'une méthode simple et s'appuyant sur peu d'hypothèses. [less ▲]

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See detailA preemption-aware on-line routing algorithm for MPLS networks
Blanchy, François; Mélon, Laurent; Leduc, Guy ULg

in Telecommunication Systems (2003), 24(2-4, OCT-DEC), 187-206

In the context of Multiprotocol Label Switching (MPLS), we look at the problem of organizing the mapping of Label Switched Paths (LSPs) in an optimal way throughout the network on the basis of a given ... [more ▼]

In the context of Multiprotocol Label Switching (MPLS), we look at the problem of organizing the mapping of Label Switched Paths (LSPs) in an optimal way throughout the network on the basis of a given objective function. This problem is highly combinatorial and makes dynamic and real-time features a difficult issue for any LSP routing scheme. For this reason, we propose a computationally efficient, though approximate, on-line scheme adapted to an incremental optimization of the network state. We also propose an integration of a computationally efficient preemption mechanism into this approximation. The efficiency of this algorithm is obtained through a very rigid but seemingly appropriate policy concerning which LSPs are appropriate for preemption. A feedback from preemption on the routing process is proposed, in order to regulate the rate of the reroutings and to tune the balance between stability and continuous reorganization in a network. [less ▲]

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See detailAn efficient decentralized on-line traffic engineering algorithm for MPLS networks
Blanchy, François; Mélon, Laurent; Leduc, Guy ULg

in Providing Quality of Service in Heterogeneous Environments (2003, August)

Multi-Protocol Label Switching (MPLS) provides ways to control the Label Switched Paths (LSPs) followed by traffic trunks in a network and thereby to better traffic engineer it. In this context, we look ... [more ▼]

Multi-Protocol Label Switching (MPLS) provides ways to control the Label Switched Paths (LSPs) followed by traffic trunks in a network and thereby to better traffic engineer it. In this context, we look at the problem of organizing the mapping of LSPs in an optimal way throughout the network on the basis of a given objective function. This problem is highly combinatorial and makes dynamic and real-time features a difficult issue for any LSP routing scheme. For this reason, we propose a computationally efficient, though approximate, on-line scheme adapted to an incremental optimization of the network state. It is then applied to a seldom mentioned traffic engineering problem: the compromise between load-balancing and traffic minimization. It is expected that clever routing strategies to balance the network load will sometimes favor longer paths in order to avoid congestion, leading to an increase of the overall network utilization. This reasoning is confirmed by our study, and we show that an improvement in network management can be made by appropriately tuning this compromise. [less ▲]

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See detailDecentralized local backup LSP calculation with efficient bandwidth sharing
Mélon, Laurent; Blanchy, François; Leduc, Guy ULg

in 10th IEEE International Conference on Telecommunications (2003, February)

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. For this type of application endto- end recovery schemes are usually considered to be far too slow. Local, fast-rerouting is the only solution which can compete with restoration times offered by SONET self-healing ring. However local restoration has a cost in terms of extra bandwidth consumed for the backup paths. Our scheme thus includes a sophisticated resource aggregation mechanism based on the concepts of "backup-backup aggregation" and "backupprimary 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-theart end-to-end recovery schemes in terms of resource reservation. 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. [less ▲]

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See detailRouting in a MPLS network featuring preemption mechanisms
Blanchy, François; Mélon, Laurent; Leduc, Guy ULg

in 10th IEEE International Conference on Telecommunications (2003, February)

In the context of Multiprotocol Label Switching (MPLS), we propose an integration of a computationally efficient preemption mechanism into a very dynamic Label Switched Paths (LSPs) routing scheme ... [more ▼]

In the context of Multiprotocol Label Switching (MPLS), we propose an integration of a computationally efficient preemption mechanism into a very dynamic Label Switched Paths (LSPs) routing scheme described in a previous paper. This preemption scheme includes a quick heuristic able to select the most interesting LSPs to reroute from a link. The efficiency of this algorithm is obtained through a very rigid but seemingly appropriate policy concerning which LSPs are appropriate for preemption. A feedback from preemption on the routing process is proposed, in order to regulate the rate of the reroutings and to tune the balance between stability and continuous reorganization in a network. This integrated traffic engineering entity is tested on the accuracy of the heuristic, the relevance of the feedback and the whole integration, the influence of the routing policy on the preemption mechanism and the reliability of the managed network. [less ▲]

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See detailModule de garantie de transmission
Reinbold, Pierre; Martin, Sylvain ULg; Bonaventure, Olivier et al

in ARTHUR - Manuel d'informatisation des urgences (2003)

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See detailSmoothing the TCP rate by learning the delay versus window size dependency
El Khayat, Ibtissam; Leduc, Guy ULg

in Lecture Notes in Computer Science (2003), 2899

We propose TCP-L, an improved version of TCP, equipped with a learning algorithm whose purpose is to avoid probing for additional bandwidth when the network conditions are known to be unfavourable. TCP-L ... [more ▼]

We propose TCP-L, an improved version of TCP, equipped with a learning algorithm whose purpose is to avoid probing for additional bandwidth when the network conditions are known to be unfavourable. TCP-L learns the relationship between its current (average) one-trip delay and its current window size when congestion occurs, leading to packet loss. After the learning phase, TCP-L will only probe for bandwidth by increasing its window if, under the current network conditions (measured by the one-trip delay), this inflated window has not previously created congestion. Simulations show that after the learning phase, TCP-L reaches a much more stable throughput, while remaining TCP-friendly, which makes it usable for a larger class of applications, including some multimedia applications that will benefit from that stability. TCP-L is a simple backward compatible extension of TCP which can thus be deployed progressively. We show that there is a benefit for the Internet to deploy TCP-L, because the overall traffic becomes smoother when the proportion of TCP-L flows increases. Finally, our learning component can also be easily embedded in other unicast or multicast transport protocols. [less ▲]

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See detailRADAR: Ring-based adaptive discovery of active neighbour routers
Martin, Sylvain ULg; Leduc, Guy ULg

in Lecture Notes in Computer Science (2002, December), 2546

The RADAR protocol and its underlying neighbourhood discovery framework extend the ANTS toolkit by giving active nodes the ability to discover dynamically other active nodes close to them without relying ... [more ▼]

The RADAR protocol and its underlying neighbourhood discovery framework extend the ANTS toolkit by giving active nodes the ability to discover dynamically other active nodes close to them without relying on any configuration file. Such an automatic discovery is the key to administration of large or sparse active networks and the first step towards an efficient active routing. Active nodes will use their local IP routing table to run an extended ring search in their domain. An Additive Increase Multiplicative Decrease control allows RADAR to discover several neighbours per physical interface without searching too far away or fixing a maximum distance a priori. The protocol is complemented by a traffic-driven discovery that can grab capsules coming from unknown nodes (mainly outside the local domain) and trigger targetted probing of those addresses. [less ▲]

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