References of "Leduc, Guy"
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See detailTriangle Inequality Violation Avoidance in Internet Coordinate Systems
Liao, Yongjun ULg; Leduc, Guy ULg

Poster (2009, August 24)

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See detailDetecting Triangle Inequality Violations in Internet Coordinate Systems
Kaafar, Mohamed Ali; Cantin, François ULg; Gueye, Cheikh Ahmadou Bamba ULg et al

in Future Networks 2009 (2009, June 18)

Internet Coordinate Systems (ICS) have been proposed as a method for estimating delays between hosts without direct measurement. However, they can only be accurate when the triangle inequality holds for ... [more ▼]

Internet Coordinate Systems (ICS) have been proposed as a method for estimating delays between hosts without direct measurement. However, they can only be accurate when the triangle inequality holds for Internet delays. Actually Triangle Inequality Violations (TIVs) are frequent and are likely to remain a property of the Internet due to routing policies or path inflation. In this paper we propose methods to detect TIVs with high confidence by observing various metrics such as the relative estimation error on the coordinates. Indeed, the detection of TIVs can be used for mitigating their impact on the ICS itself, by excluding some disturbing nodes from clusters running their own ICS, or more generally by improving their neighbor selection mechanism. [less ▲]

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See detailDetecting Triangle Inequality Violations in Internet Coordinate Systems by Supervised Learning
Liao, Yongjun ULg; Kaafar, Mohamed Ali; Gueye, Bamba et al

in Lecture Notes in Computer Science (2009, May 12), 5550

Internet Coordinates Systems (ICS) are used to predict Internet distances with limited measurements. However the precision of an ICS is degraded by the presence of Triangle Inequality Violations (TIVs ... [more ▼]

Internet Coordinates Systems (ICS) are used to predict Internet distances with limited measurements. However the precision of an ICS is degraded by the presence of Triangle Inequality Violations (TIVs). Simple methods have been proposed to detect TIVs, based e.g. on the empirical observation that a TIV is more likely when the distance is underestimated by the coordinates. In this paper, we apply supervised machine learning techniques to try and derive more powerful criteria to detect TIVs. We first show that (ensembles of) Decision Trees (DTs) learnt on our datasets are very good models for this problem. Moreover, our approach brings out a discriminative variable (called OREE), which combines the classical estimation error with the variance of the estimated distance. This variable alone is as good as an ensemble of DTs, and provides a much simpler criterion. If every node of the ICS sorts its neighbours according to OREE, we show that cutting these lists after a given number of neighbours, or when OREE crosses a given threshold value, achieves very good performance to detect TIVs. [less ▲]

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See detailBGP-aware IGP Link Weight Optimization in Presence of Route Reflectors
Balon, Simon ULg; Leduc, Guy ULg

in IEEE INFOCOM 2009 (2009, April)

The first generation of IGP Link Weight Optimizers (LWOs) was based on presumably invariant intra-domain traffic matrices only, ignoring the fact that updating link weights had a side effect on these ... [more ▼]

The first generation of IGP Link Weight Optimizers (LWOs) was based on presumably invariant intra-domain traffic matrices only, ignoring the fact that updating link weights had a side effect on these traffic matrices due to hot-potato routing, thus result- ing in suboptimal link weight settings, and sometimes to very bad performance. The second generation of IGP LWOs, referred to as BGP-aware LWOs, has been able to optimize link weights while taking hot-potato effects into account. However, these tools relied on the complete visibility assumption fulfilled by e.g. a full-mesh iBGP configu- ration. This paper proposes a third generation LWO, still BGP-aware, but also able to work with iBGP con- figurations based on route reflectors, which usually hide some reachability information from routers. This partial visibility may cause various problems, including path deflections (i.e., the actual egress router is not the expected one), which may in turn create forwarding loops. Our LWO embeds a BGP routing solver which can always predict the actual egress router, even when route reflectors are used. It can also forbid solutions leading to path deflection. Its efficiency is evaluated on a real dataset, and compared to other LWOs. [less ▲]

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See detailRouting Based on Delivery Distributions in Predictable Disruption Tolerant Networks
François, Jean-Marc; Leduc, Guy ULg

in Ad hoc Networks (2009), 7(1), 219-229

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’ tradeoff: 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 detailInterpreted Active Packets for Ephemeral State Processing Routers
Martin, Sylvain ULg; Leduc, Guy ULg

in Lecture Notes in Computer Science (2009), 4388

We propose WASP (lightweight and World-friendly Active packets for ephemeral State Processing), a new active platform based on Ephemeral State designed to allow bytecode interpretation on programmable ... [more ▼]

We propose WASP (lightweight and World-friendly Active packets for ephemeral State Processing), a new active platform based on Ephemeral State designed to allow bytecode interpretation on programmable datapath elements. We designed WASP to be a good compromise between flexibility (e.g. offering solutions in quality-adaptive multimedia flows, service discovery or mobility support) and safety (i.e. protection of router and network resource). [less ▲]

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See detailA Self-Organized clustering scheme for overlay networks
Cantin, François ULg; Gueye, Cheikh Ahmadou Bamba ULg; Kaafar, Mohamed Ali ULg et al

in Lecture Notes in Computer Science (2008, December), 5343

Hierarchical approaches, where nodes are clustered based on their network distances, have been shown to allow for robust and scalable topology-aware overlays. Moreover, recent research works have shown ... [more ▼]

Hierarchical approaches, where nodes are clustered based on their network distances, have been shown to allow for robust and scalable topology-aware overlays. Moreover, recent research works have shown that cluster-based deployments of Internet Coordinates Systems (ICS), where nodes estimate both intra-cluster and inter-cluster distances, do mitigate the impact of Triangle Inequality Violations (TIVs) on the distance predictions, and hence offer more accurate internet latency estimations. To allow the construction of such useful clusters we propose a self-organized distributed clustering scheme. For better scalability and efficiency, our algorithm uses the coordinates of a subset of nodes, known by running an ICS system, as first approximations of node positions. We designed and evaluated two variants of this algorithm. The first one, based on some cooperation among nodes, aims at reducing the expected time to construct clusters. The second variant, where nodes are selfish, aims at reducing the induced communication overhead. [less ▲]

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See detailOverlay Routing using Coordinate Systems
Cantin, François ULg; Gueye, Cheikh Ahmadou Bamba ULg; Kaafar, Mohamed Ali ULg et al

Poster (2008, December)

We address the problem of finding indirect overlay paths that reduce the latency between pairs of nodes in an overlay. To this end we propose to rely on an Internet Coordinate System (ICS), namely Vivaldi ... [more ▼]

We address the problem of finding indirect overlay paths that reduce the latency between pairs of nodes in an overlay. To this end we propose to rely on an Internet Coordinate System (ICS), namely Vivaldi, to estimate RTTs and help find these interesting detours. We define two initial criteria to illustrate our approach and assess their true/false positive rates. [less ▲]

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See detailCombined Intra- and Inter-domain Traffic Engineering using Hot-Potato Aware Link Weights Optimization
Balon, Simon ULg; Leduc, Guy ULg

in ACM SIGMETRICS Performance Evaluation Review (2008), 36(1), 441-442

A well-known approach to intradomain traffic engineering consists in finding the set of link weights that minimizes a network-wide objective function for a given intradomain traffic matrix. This approach ... [more ▼]

A well-known approach to intradomain traffic engineering consists in finding the set of link weights that minimizes a network-wide objective function for a given intradomain traffic matrix. This approach is inadequate because it ignores a potential impact on interdomain routing due to hot-potato routing policies. This may result in changes in the intradomain traffic matrix that have not been anticipated by the link weights optimizer, possibly leading to degraded network performance. <br /> <br />We propose a BGP-aware link weights optimization method that takes these hot-potato effects into account. This method uses the interdomain traffic matrix and other available BGP data, to extend the intradomain topology with external virtual nodes and links, on which all the well-tuned heuristics of a classical link weights optimizer can be applied. Our method can also optimize the traffic on the interdomain peering links. [less ▲]

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See detailTOTEM(v3.2) - Toolbox of Traffic Engineering Methods
Balon, Simon; Delcourt, Olivier; Lepropre, Jean et al

Software (2008)

TOTEM is a toolbox for traffic engineering methods. TOTEM is licensed under the GPL (GNU General Public License) version 2.0. This open-source toolbox provides a set of tools to allow network operators to ... [more ▼]

TOTEM is a toolbox for traffic engineering methods. TOTEM is licensed under the GPL (GNU General Public License) version 2.0. This open-source toolbox provides a set of tools to allow network operators to traffic engineer their network. It can also be used by researchers who implement new techniques. [less ▲]

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See detailTowards a Two-Tier Internet coordinate system to mitigate the impact of Triangle Inequality Violations
Kaafar, Mohamed Ali ULg; Gueye, Cheikh Ahmadou Bamba ULg; Cantin, François ULg et al

in Lecture Notes in Computer Science (2008, May), 4982

Routing policies or path inflation can give rise to violations of the Triangle Inequality with respect to delay (RTTs) in the Internet. In network coordinate systems, such Triangle Inequality Violations ... [more ▼]

Routing policies or path inflation can give rise to violations of the Triangle Inequality with respect to delay (RTTs) in the Internet. In network coordinate systems, such Triangle Inequality Violations (TIVs) will introduce inaccuracy, as nodes in this particular case could not be embedded into any metric space. In this paper, we consider these TIVs as an inherent and natural property of the Internet; rather than trying to remove them, we consider characterizing them and mitigating their impact on distributed coordinate systems. In a first step, we study TIVs existing in the Internet, using different metrics in order to quantify various levels of TIVs’ severity. Our results show that path lengths do have an effect on the impact of these TIVs. In particular, the shorter the link between any two nodes is, the less severe TIVs involved in are. In a second step, we do leverage our study to reduce the impact of TIVs on coordinate systems. We focus on the particular case of the Vivaldi coordinate system and we explore how TIVs may impact its accuracy and stability. In particular, we observed correlation between the (in)stability and high effective error of nodes’ coordinates with respect to their involvement in TIVs situations. We finally propose a Two-Tier architecture opposed to a flat structure of Vivaldi that do mitigate the effect of TIVs on the distances predictions. [less ▲]

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See detailAn overlay maintenance protocol for overlay routing on top of ad hoc networks
Calomme, Sandrine; Leduc, Guy ULg

in Lecture Notes in Computer Science (2008, May), 4982

The protocol described in this paper builds and maintains an overlay topology on top of an ad hoc network. The overlay is intended to be used by a routing application. As flooding is a key component of ... [more ▼]

The protocol described in this paper builds and maintains an overlay topology on top of an ad hoc network. The overlay is intended to be used by a routing application. As flooding is a key component of many route discovery mechanisms in MANETs, we evaluate the delivery percentage, bandwidth consumption and time duration of flooding a message on the overlay. We also consider the overlay path stretch as an indicator for the data transfer transmission time. The protocol does not require any information from the underlay routing protocol, nor cooperation from the nodes that do not belong to the overlay. Each overlay node maintains a set of nearest overlay nodes and exchanges its neighbourhood information with them in order to select useful overlay links. Resilience is afforded by setting a minimum number of overlay neighbours. The performance observed over OLSR are good, for all overlay densities and mobility level studied. [less ▲]

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See detailExplication et réduction de l’impact des violations d’inégalités triangulaires dans Vivaldi
Cantin, François ULg; Gueye, Cheikh Ahmadou Bamba ULg; Kaafar, Mohamed Ali ULg et al

in CFIP'2008 (2008, March)

Les systèmes de coordonnées sont des systèmes distribués ayant pour but, à partir de mesures de distance (par exemple RTT) entre certaines paires de noeuds, d’associer des coordonnées à chaque noeud dans ... [more ▼]

Les systèmes de coordonnées sont des systèmes distribués ayant pour but, à partir de mesures de distance (par exemple RTT) entre certaines paires de noeuds, d’associer des coordonnées à chaque noeud dans un espace métrique. Toutefois, de tels systèmes ne fonctionnent pas correctement lorsque les distances mesurées ne respectent pas les inégalités triangulaires. Or, les violations de ces inégalités, appelées TIV, sont fréquentes dans l’Internet. Nous proposons une étude approfondie de l’impact des TIV sur le système de coordonnées Vivaldi. Nous quantifions et expliquons les erreurs de prédiction de distance et l’instabilité des coordonnées causées par les TIV selon leur fréquence et leur sévérité. Nous montrons aussi que la distance entre deux noeuds, mesurée par le RTT, est corrélée à la probabilité d’existence d’une TIV. Enfin, nous recommandons un système de coordonnées hiérarchique, et nous montrons, par des simulations sur une matrice de délais réelle, qu’une telle approche réduit l’impact des TIV. [less ▲]

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See detailCan Forwarding Loops Appear when Activating iBGP Multipath Load Sharing?
Balon, Simon ULg; Leduc, Guy ULg

in Lecture Notes in Computer Science (2007, November), 4866

We analyse the possible consequences of activating iBGP multipath load sharing in a given domain (or AS), which allows for load balancing over multiple exit routers. It has been stated that interdomain ... [more ▼]

We analyse the possible consequences of activating iBGP multipath load sharing in a given domain (or AS), which allows for load balancing over multiple exit routers. It has been stated that interdomain routing loops may appear in this case. We show that under reasonable assumptions (which reflect commercial relationships between ASes) such routing loops cannot appear. Furthermore we show that even if theses assumptions are not met, routing loops can only be transient. [less ▲]

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See detailEfficient and Resilient Overlay Topologies over Ad Hoc Networks
Calomme, Sandrine; Leduc, Guy ULg

in Lecture Notes in Computer Science (2007, September), 4725

We discuss what kind of overlay topology should be pro-actively built before an overlay routing protocol enters a route search process on top of it. The basic overlay structures we study are the K-Nearest ... [more ▼]

We discuss what kind of overlay topology should be pro-actively built before an overlay routing protocol enters a route search process on top of it. The basic overlay structures we study are the K-Nearest Neighbours overlay topologies, connecting every overlay node to its K nearest peers. We introduce a family of optimizations, based on a pruning rule. As flooding is a key component of many route discovery mechanisms in MANETs, our performance study focusses on the delivery percentage, bandwidth consumption and time duration of flooding on the overlay. We also consider the overlay path stretch and the overlay nodes degree as respective indicators for the data transfer transmission time and overlay resilience. We finally recommend to optimize the K-Nearest Neighbours overlay topologies with the most selective pruning rule and, if necessary, to set a minimal bound on the overlay node degree for improving resilience. [less ▲]

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See detailMachine-learnt versus analytical models of TCP throughput
El Khayat, Ibtissam; Geurts, Pierre ULg; Leduc, Guy ULg

in Computer Networks (2007), 51(10), 2631-2644

We first study the accuracy of two well-known analytical models of the average throughput of long-term TCP flows, namely the so-called SQRT and PFTK models, and show that these models are far from being ... [more ▼]

We first study the accuracy of two well-known analytical models of the average throughput of long-term TCP flows, namely the so-called SQRT and PFTK models, and show that these models are far from being accurate in general. Our simulations, based on a large set of long-term TCP sessions, 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. We then investigate the reasons of this inaccuracy, and show that it is largely due to the lack of discrimination between the two packet loss detection methods used by TCP, namely by triple duplicate acknowledgements or by timeout: expirations. We then apply various machine learning techniques to infer new models of the average TCP throughput. We show that they are more accurate than the SQRT and PFTK models, even without the above discrimination, and are further improved when we allow the machine-learnt models to distinguish the two loss detection techniques. Although our models are not analytical formulas, they can be plugged in transport protocols to make them TCP-Friendly. Our results also suggest that analytical models of the TCP throughput should certainly benefit from the incorporation of the timeout loss rate. (C) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailBasic Abstractions for an Autonomic Network Architecture
Jelger, Christophe; Tschudin, Christian; Schmid, Stefan et al

in First IEEE Workshop on Autonomic and Opportunistic Communications (2007, June)

The ANA (Autonomic Network Architecture) project aims at providing a framework to flexibly host, interconnect, and federate multiple heterogeneous networks in an autonomic way, i.e. without requiring ... [more ▼]

The ANA (Autonomic Network Architecture) project aims at providing a framework to flexibly host, interconnect, and federate multiple heterogeneous networks in an autonomic way, i.e. without requiring active human intervention. The guiding design principle is to strive for a maximum degree of flexibility at all levels of the architecture in order to inherently support heterogeneity and evolution. This paper describes the core abstractions and concepts of ANA (as defined during the first year of the project) and introduces their basic operation and interaction. While not autonomic themselves, the core architectural principles of ANA will enable autonomicity by not imposing a "one-size-fits-all" approach where protocols and paradigms are fixed by the architecture. We indeed argue that only the capacity of the network to be polyfunctional and fully adaptable will justify the label ' autonomic'. A prototype ofANA is currently being developed and will be released in 2008: the goal is to demonstrate the feasibility of autonomic networking within the 4 years of the project. [less ▲]

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See detailTraffic Engineering an Operational Network with the TOTEM Toolbox
Balon, Simon ULg; Lepropre, Jean; Delcourt, Olivier et al

in IEEE Transactions on Network and Service Management (2007), 4(1), 51-61

We explain how the TOTEM toolbox can be used to engineer an operational network. TOTEM is an open source TOolbox for Traffic Engineering Methods which covers IP-based and MPLS-based intradomain traffic ... [more ▼]

We explain how the TOTEM toolbox can be used to engineer an operational network. TOTEM is an open source TOolbox for Traffic Engineering Methods which covers IP-based and MPLS-based intradomain traffic engineering (TE) algorithms, but also interdomain TE. In this paper, we use the toolbox as an off-line simulator to optimise the traffic of an operational network. To help an operator to choose between an IP-based or MPLS-based solution, or to find the best way to load-balance a network for a given traffic, our case study compares several IP and MPLS routing algorithms, evaluates the impact of hot-potato routing on the intradomain traffic matrix, and analyses the worst-case link failure. This study reveals the power of a toolbox that federates many traffic engineering algorithms. [less ▲]

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See detailAP and MN-centric Mobility Prediction: A Comparative Study Based On Wireless Traces
François, Jean-Marc; Leduc, Guy ULg

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

The mobility prediction problem is defined as guessing a mobile node's next access point as it moves through a wireless network. Those predictions help take proactive measures in order to guarantee a ... [more ▼]

The mobility prediction problem is defined as guessing a mobile node's next access point as it moves through a wireless network. Those predictions help take proactive measures in order to guarantee a given quality of service. Prediction agents can be divided into two main categories: agents related to a specific terminal (responsible for anticipating its own movements) and those related to an access point (which predict the next access point of all the mobiles connected through it). This paper aims at comparing those two schemes using real traces of a large WiFi network. Several observations are made, such as the difficulties encountered to get a reliable trace of mobiles motion, the unexpectedly small difference between both methods in terms of accuracy, and the inadequacy of commonly admitted hypotheses (such as the different motion behaviours between the week-end and the rest of the week). [less ▲]

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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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