Browse ORBi by ORBi project

- Background
- Content
- Benefits and challenges
- Legal aspects
- Functions and services
- Team
- Help and tutorials

Efficient and Resilient Overlay Topologies over Ad Hoc Networks ; Leduc, Guy 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 ▲] Detailed reference viewed: 99 (2 ULg)Immersive digital games: the interfaces for next-generation e-learning? ; ; et al in Lecture Notes in Computer Science (2007), 4556(2007), 647-656 The intrinsic motivation to play, and therefore to learn, that might be provided by digital educational games teases researchers and developers. However, existing educational games often fail in their ... [more ▼] The intrinsic motivation to play, and therefore to learn, that might be provided by digital educational games teases researchers and developers. However, existing educational games often fail in their attempt to compete with commercial games and to provide successful learning. Often some learning is added to digital games or some gameplay is added to educational applications. Successful educational games, however, require merging professional game design with sound pedagogical strategies, creating a new hybrid format. Moreover, a methodology is required that allows continuously balancing gaming and learning challenges and the learner's abilities and knowledge in order to retain an immersive gaming experience. In this article we introduce approaches to game design and didactic design, as well as a framework for adaptive interventions in educational games. [less ▲] Detailed reference viewed: 33 (3 ULg)A Generalization of Cobham's Theorem to Automata over Real Numbers Boigelot, Bernard ; Brusten, Julien in Lecture Notes in Computer Science (2007, July), 4596 This paper studies the expressive power of finite-state automata recognizing sets of real numbers encoded positionally. It is known that the sets that are definable in the first-order additive theory of ... [more ▼] This paper studies the expressive power of finite-state automata recognizing sets of real numbers encoded positionally. It is known that the sets that are definable in the first-order additive theory of real and integer variables (R, Z, +, <) can all be recognized by weak deterministic Büchi automata, regardless of the encoding base r > 1. In this paper, we prove the reciprocal property, i.e., that a subset of R that is recognizable by weak deterministic automata in every base r > 1 is necessarily definable in (R, Z, +, <). This result generalizes to real numbers the well-known Cobham's theorem on the finite-state recognizability of sets of integers. Our proof gives interesting insight into the internal structure of automata recognizing sets of real numbers, which may lead to efficient data structures for handling these sets. [less ▲] Detailed reference viewed: 140 (33 ULg)Delivery Guarantees In Predictable Disruption Tolerant Networks ; Leduc, Guy 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 ▲] Detailed reference viewed: 13 (2 ULg)AP and MN-centric Mobility Prediction: A Comparative Study Based On Wireless Traces ; Leduc, Guy 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 ▲] Detailed reference viewed: 23 (4 ULg)Problems and Challenges of Image-Guided Neurosurgical Navigation and Intervention Verly, Jacques ; ; et al in Lecture Notes in Computer Science (2006, November), 4263 Detailed reference viewed: 20 (8 ULg)Approximate Policy Iteration for Closed-Loop Learning of Visual Tasks Jodogne, Sébastien ; Briquet, Cyril ; Piater, Justus in Lecture Notes in Computer Science (2006, September), 4212 Approximate Policy Iteration (API) is a reinforcement learning paradigm that is able to solve high- dimensional, continuous control problems. We propose to exploit API for the closed-loop learning of ... [more ▼] Approximate Policy Iteration (API) is a reinforcement learning paradigm that is able to solve high- dimensional, continuous control problems. We propose to exploit API for the closed-loop learning of mappings from images to actions. This approach requires a family of function approximators that maps visual percepts to a real-valued function. For this purpose, we use Regression Extra-Trees, a fast, yet accurate and versatile machine learning algorithm. The inputs of the Extra-Trees consist of a set of visual features that digest the informative patterns in the visual signal. We also show how to parallelize the Extra-Tree learning process to further reduce the computational expense, which is often essential in visual tasks. Experimental results on real-world images are given that indicate that the combination of API with Extra-Trees is a promising framework for the interactive learning of visual tasks. [less ▲] Detailed reference viewed: 36 (14 ULg)How well do traffic engineering objective functions meet TE requirements? Balon, Simon ; Skivée, Fabian ; Leduc, Guy 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 ▲] Detailed reference viewed: 37 (6 ULg)On the accuracy of analytical models of TCP throughput ; Geurts, Pierre ; Leduc, Guy 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 ▲] Detailed reference viewed: 36 (6 ULg)Projective relations in a 3D environment Billen, Roland ; in Lecture Notes in Computer Science (2006), 4197 This paper presents a model for positional relations among bodies of arbitrary shape in three dimensions. It is based on an existing model for projective relations among regions in two dimensions. The ... [more ▼] This paper presents a model for positional relations among bodies of arbitrary shape in three dimensions. It is based on an existing model for projective relations among regions in two dimensions. The motivation is to provide a formal qualitative spatial relations model for emerging 3D applications. Two sets of relations are defined: ternary projective relations based on the concept of collinearity between a primary object and two reference objects and quaternary projective relations based on the concept of coplanarity between a primary object and three reference objects. Four sets of JEPD relations are defined for points and bodies in R-3. [less ▲] Detailed reference viewed: 58 (20 ULg)Robust analysis of silhouettes by morphological size distributions Barnich, Olivier ; JODOGNE, Sébastien ; Van Droogenbroeck, Marc in Lecture Notes in Computer Science (2006), 4179 We address the topic of real-time analysis and recognition of silhouettes. The method that we propose first produces object features obtained by a new type of morphological operators, which can be seen as ... [more ▼] We address the topic of real-time analysis and recognition of silhouettes. The method that we propose first produces object features obtained by a new type of morphological operators, which can be seen as an extension of existing granulometric filters, and then insert them into a tailored classification scheme. Intuitively, given a binary segmented image, our operator produces the set of all the largest rectangles that can be wedged inside any connected component of the image. The latter are obtained by a standard background subtraction technique and morphological filtering. To classify connected components into one of the known object categories, the rectangles of a connected component are submitted to a machine learning algorithm called EXtremely RAndomized trees (Extra-trees). The machine learning algorithm is fed with a static database of silhouettes that contains both positive and negative instances. The whole process, including image processing and rectangle classification, is carried out in real-time. Finally we evaluate our approach on one of today's hot topics: the detection of human silhouettes. We discuss experimental results and show that our method is stable and computationally effective. Therefore, we assess that algorithms like ours introduce new ways for the detection of humans in video sequences. [less ▲] Detailed reference viewed: 119 (15 ULg)The power of hybrid acceleration Boigelot, Bernard ; in Lecture Notes in Computer Science (2006), 4144 This paper addresses the problem of computing symbolically the set of reachable configurations of a linear hybrid automaton. A solution proposed in earlier work consists in exploring the reachable ... [more ▼] This paper addresses the problem of computing symbolically the set of reachable configurations of a linear hybrid automaton. A solution proposed in earlier work consists in exploring the reachable configurations using an acceleration operator for computing the iterated effect of selected control cycles. Unfortunately, this method imposes a periodicity requirement on the data transformations labeling these cycles, that is not always satisfied in practice. This happens in particular with the important subclass of timed automata, even though it is known that the paths of such automata have a periodic behavior. The goal of this paper is to broaden substantially the applicability of hybrid acceleration. This is done by introducing powerful reduction rules, aimed at translating hybrid data transformations into equivalent ones that satisfy the periodicity criterion. In particular, we show that these rules always succeed in the case of timed automata. This makes it possible to compute an exact symbolic representation of the set of reachable configurations of a linear hybrid automaton, with a guarantee of termination over the subclass of timed automata. Compared to other known solutions to this problem, our method is simpler, and applicable to a much larger class of systems. [less ▲] Detailed reference viewed: 42 (8 ULg)Task-Driven Discretization of the Joint Space of Visual Percepts and Continuous Actions Jodogne, Sébastien ; Piater, Justus in Lecture Notes in Computer Science (2006), 4212 Detailed reference viewed: 7 (4 ULg)Improving TCP in wireless networks with an adaptive machine-learnt classifier of packet loss causes ; Geurts, Pierre ; Leduc, Guy 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 ▲] Detailed reference viewed: 36 (5 ULg)An active platform as middleware for services and communities discovery Martin, Sylvain ; Leduc, Guy 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 ▲] Detailed reference viewed: 29 (12 ULg)Semantics of Collinearity Among Regions Billen, Roland ; in Lecture Notes in Computer Science (2005) Detailed reference viewed: 29 (12 ULg)Abstract numeration systems and tilings ; Rigo, Michel in Lecture Notes in Computer Science (2005), 3618 An abstract numeration system is a triple S = (L, Sigma, <) where (Z, <) is a totally ordered alphabet and L a regular language over Z; the associated numeration is defined as follows: by enumerating the ... [more ▼] An abstract numeration system is a triple S = (L, Sigma, <) where (Z, <) is a totally ordered alphabet and L a regular language over Z; the associated numeration is defined as follows: by enumerating the words of the regular language L over Z with respect to the induced genealogical ordering, one obtains a one-to-one correspondence between N and L. Furthermore, when the language L is assumed to be exponential, real numbers can also be expanded. The aim of the present paper is to associate with S a self-replicating multiple tiling of athe space, under the following assumption: the adjacency matrix of the trimmed minimal automaton recognizing L is primitive with a dominant eigenvalue being a Pisot unit. This construction generalizes the classical constructions performed for Rauzy fractals associated with Pisot substitutions [16], and for central tiles associated with a Pisot beta-numeration [23]. [less ▲] Detailed reference viewed: 35 (4 ULg)MECOSIG adapted to the design of distributed GIS ; ; et al in Lecture Notes in Computer Science (2005), 3762 For more than ten years MECOSIG has been used as a method for GIS design and implementation in various national and international projects achieved in our laboratory. During a decade, the method has been ... [more ▼] For more than ten years MECOSIG has been used as a method for GIS design and implementation in various national and international projects achieved in our laboratory. During a decade, the method has been progressively improved and extended without modification of its basic principles. However the emergence of distributed GIS, implying several organizations capable to play various roles, requires the reappraisal of the methodology. New concerns are identified and a collection of new tools must be deployed. Taking the most of various recent researches completed for public authorities in Belgium, this paper presents some significant adaptations of the original MECOSIG method in order to cope with a distributed GIS environment. [less ▲] Detailed reference viewed: 39 (1 ULg)Segment and combine approach for non-parametric time-series classification Geurts, Pierre ; Wehenkel, Louis in Lecture Notes in Computer Science (2005), 3721 This paper presents a novel, generic, scalable, autonomous, and flexible supervised learning algorithm for the classification of multivariate and variable length time series. The essential ingredients of ... [more ▼] This paper presents a novel, generic, scalable, autonomous, and flexible supervised learning algorithm for the classification of multivariate and variable length time series. The essential ingredients of the algorithm are randomization, segmentation of time-series, decision tree ensemble based learning of subseries classifiers, combination of subseries classification by voting, and cross-validation based temporal resolution adaptation. Experiments are carried out with this method on 10 synthetic and real-world datasets. They highlight the good behavior of the algorithm on a large diversity of problems. Our results are also highly competitive with existing approaches from the literature. [less ▲] Detailed reference viewed: 54 (5 ULg)A distributed algorithm for weighted max-min fairness in MPLS networks Skivée, Fabian ; Leduc, Guy 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 ▲] Detailed reference viewed: 50 (2 ULg) |
||