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Guy Leduc - Publications ORBI
Wassermann, S., Casas, P., Donnet, B., Leduc, G., & Mellia, M. (2016). On the Analysis of Internet Paths with DisNETPerf, a Distributed Paths Performance Analyzer. Proc. 10th IEEE Workshop on Network Measurements (WNM).
Peer reviewed
Traceroute is the most widely used Internet path analysis tool today to study the topology of the Internet and to diagnose routing failures as well as poor performance events. A major limitation of traceroute ...
Liao, Y., Du, W., & Leduc, G. (2015). A Lightweight Network Proximity Service Based On Neighborhood Models. 22nd IEEE Symposium on Communications and Vehicular Technology in the Benelux (SCVT). IEEE.
Peer reviewed
This paper proposes a network proximity service based on the neighborhood models used in recommender systems. Unlike previous approaches, our service infers network proximity without trying to recover the ...
Du, W., Liao, Y., Tao, N., Geurts, P., Fu, X., & Leduc, G. (2015). Rating Network Paths for Locality-Aware Overlay Construction and Routing. IEEE/ACM Transactions on Networking, 23(5), 1661-1673.
Peer reviewed (verified by ORBi)
This paper investigates the rating of network paths, i.e. acquiring quantized measures of path properties such as round-trip time and available bandwidth. Comparing to finegrained measurements, coarse ...
Papadimitriou, D., Ben Houidi, Z., Ghamri-Doudane, Rossi, D., Milanesio, M., Casas, P., D'Alconzo, A., Tego, E., Matera, F., Dusi, M., Szemethy, T., Mathé, D., Traverso, S., Finamore, A., Leontiadis, I., Baltrunas, L., Grunenburger, Y., Donnet, B., Leduc, G., & Liao, Y. (2013). Design of Analysis Modules.
This public deliverable describes the design and specification of a first set of basic analysis modules for addressing the use cases identified in WP1. The document focuses on the required algorithms, which ...
Liao, Y., Du, W., Geurts, P., & Leduc, G. (2013). DMFSGD: A Decentralized Matrix Factorization Algorithm for Network Distance Prediction. IEEE/ACM Transactions on Networking, 21(5), 1511-1524.
Peer reviewed (verified by ORBi)
The knowledge of end-to-end network distances is essential to many Internet applications. As active probing of all pairwise distances is infeasible in large-scale networks, a natural idea is to measure a ...
Ghrab, A., Skhiri, S., Koener, H., & Leduc, G. (2013, May). Towards a Standards-Based Cloud Service Manager. Poster session presented at 3rd International Conference on Cloud Computing and Services Science (CLOSER 2013), Aachen, Germany.
Peer reviewed
Migrating services to the cloud brings all the benefits of elasticity, scalability and cost-cutting. However, migrating services among different cloud infrastructures or outside of the cloud is not an obvious ...
Jung, T., Martin, S., Nassar, M., Ernst, D., & Leduc, G. (2013). Outbound SPIT Filter with Optimal Performance Guarantees. Computer Networks, 57(7), 1630–1643.
Peer reviewed (verified by ORBi)
This paper presents a formal framework for identifying and filtering SPIT calls (SPam in Internet Telephony) in an outbound scenario with provable optimal performance. In so doing, our work is largely ...
Du, W., Liao, Y., Geurts, P., & Leduc, G. (2012). Ordinal Rating of Network Performance and Inference by Matrix Completion (arXiv:1211.0447).
This paper addresses the large-scale acquisition of end-to-end network performance. We made two distinct contributions: ordinal rating of network performance and inference by matrix completion. The former ...
Jung, T., Martin, S., Ernst, D., & Leduc, G. (2012). Contextual Multi-armed Bandits for the Prevention of Spam in VoIP Networks. Eprint/Working paper retrieved from http://orbi.ulg.ac.be/handle/2268/115524.
In this paper we argue that contextual multi-armed bandit algorithms could open avenues for designing self-learning security modules for computer networks and related tasks. The paper has two contributions: a ...
Martin, S., Chiarello, L., & Leduc, G. (2012). DISco: a Distributed Information Store for Network Challenges and Their Outcome. In J., Keeney & J., Serrat (Eds.), 5th International workshop on Distributed Autonomous Network Management Systems (pp. 6).
Peer reviewed
We present the design of DISco, a storage and communication middleware that enables distributed and task-centric autonomic control of networks. DISco allows multi-agent identification of anomalous situations ...
Martin, S., Chiarello, L., & Leduc, G. (2012). DISco: a Distributed Information Store for network Challenges and their Outcome (arXiv:1201.3073v1). arXiv.
We present DISco, a storage and communication middleware designed to enable distributed and task-centric autonomic control of networks. DISco is designed to enable multi-agent identification of anomalous ...
Liao, Y., Du, W., Geurts, P., & Leduc, G. (2012). DMFSGD: A Decentralized Matrix Factorization Algorithm for Network Distance Prediction (arXiv:1201.1174).
The knowledge of end-to-end network distances is essential to many Internet applications. As active probing of all pairwise distances is infeasible in large-scale networks, a natural idea is to measure a few ...
Jung, T., Martin, S., Ernst, D., & Leduc, G. (2012). Contextual Multi-armed Bandits for Web Server Defense. In A., Hussein (Ed.), Proceedings of 2012 International Joint Conference on Neural Networks (IJCNN) (pp. 8). IEEE.
Peer reviewed
In this paper we argue that contextual multi-armed bandit algorithms could open avenues for designing self-learning security modules for computer networks and related tasks. The paper has two contributions ...
Jung, T., Martin, S., Ernst, D., & Leduc, G. (2012). SPRT for SPIT: Using the Sequential Probability Ratio Test for Spam in VoIP Prevention. Proc. of 6th International Conference on Autonomous Infrastructure, Management and Security. Springer Berlin / Heidelberg.
Peer reviewed
This paper presents the first formal framework for identifying and filtering SPIT calls (SPam in Internet Telephony) in an outbound scenario with provable optimal performance. In so doing, our work deviates ...
Liao, Y., Du, W., Geurts, P., & Leduc, G. (2011). Decentralized Prediction of End-to-End Network Performance Classes. Proc. of the 7th International Conference on emerging Networking EXperiments and Technologies (CoNEXT). ACM.
Peer reviewed
In large-scale networks, full-mesh active probing of end-to-end performance metrics is infeasible. Measuring a small set of pairs and predicting the others is more scalable. Under this framework, we formulate ...
Nassar, M. A., Martin, S., Leduc, G., & Festor, O. (2011). Using Decision Trees for Generating Adaptive SPIT Signatures. Proc. of the 4th International Conference on Security of Information and Networks (SIN 2011). ACM.
Peer reviewed
With the spread of new and innovative Internet services such as SIP-based communications, the challenge of protecting and defending these critical applications has been raised. In particular, SIP firewalls ...
Cantin, F., & Leduc, G. (2011). Finding Routing Shortcuts using an Internet Coordinate System. Lecture Notes in Computer Science, 6557, 56-67.
Peer reviewed
Overlay routing is a promising way to improve the quality of service in the Internet but its main drawback is scalability: measuring the characteristics of the paths, exchanging the measurement results between ...
Liao, Y., Geurts, P., & Leduc, G. (2010). Network Distance Prediction Based on Decentralized Matrix Factorization. Lecture Notes in Computer Science, 6091, 15-26.
Peer reviewed
Network Coordinate Systems (NCS) are promising techniques to predict unknown network distances from a limited number of measurements. Most NCS algorithms are based on metric space embedding and suffer from ...
El Khayat, I., Geurts, P., & Leduc, G. (2010). Enhancement of TCP over wired/wireless networks with packet loss classifiers inferred by supervised learning. Wireless Networks, 16(2), 273-290.
Peer reviewed (verified by ORBi)
TCP is suboptimal in heterogeneous wired/wireless networks because it reacts in the same way to losses due to congestion and losses due to link errors. In this paper, we propose to improve TCP performance in ...
Gueye, C. A. B., & Leduc, G. (2009). Resolving the Noxious Effect of Churn on Internet Coordinate Systems. Lectures Notes in Computer Science, 5918, 162-173.
Peer reviewed
Internet Coordinate Systems (ICS) provide easy and practical latency predictions in the Internet. However, peer dynamics (i.e, churn), which is an in- herent property of peer-to-peer (P2P) systems, affects ...
Cantin, F., Leduc, G., & Gueye, C. A. B. (2009). Transformation non linéaire des distances : une solution au problème des violations des inégalités triangulaires dans les systèmes de coordonnées ? CFIP'2009. HAL INRIA.
Peer reviewed
Network coordinate systems embed delay measurements (e.g. RTT) between Internet nodes into some metric space. It is well known that triangle inequality violations by the measured delays are a source of ...
Soldani, C., & Leduc, G. (2009). Optimisation des débits des couches d'une transmission vidéo multipoint avec une meilleure prise en compte du surcoût d'encodage. CFIP'2009. HAL INRIA.
Peer reviewed
In video stream transmission, one often proposes to solve the problem of the heterogeneity of the receivers by dividing the stream into several cumulative layers distributed over multicast transmission. A ...
Martin, S., & Leduc, G. (2009). A Practical Bytecode Interpreter for Programmable Routers on Network Processor. Computer Networks, 53(15), 2740-2751.
Peer reviewed (verified by ORBi)
WASP is a programmable router platform that allows end-hosts to store ephemeral state in routers along the path of IP flows and to execute packet-attached bytecode that processes this data. We exploit ...
Kaafar, M. A., Cantin, F., Gueye, C. A. B., & Leduc, G. (2009). Detecting Triangle Inequality Violations in Internet Coordinate Systems. Future Networks 2009.
Peer reviewed
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 ...
Liao, Y., Kaafar, M. A., Gueye, B., Cantin, F., Geurts, P., & Leduc, G. (2009). Detecting Triangle Inequality Violations in Internet Coordinate Systems by Supervised Learning. Lecture Notes in Computer Science, 5550, 352-363.
Peer reviewed
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 ...
Balon, S., & Leduc, G. (2009). BGP-aware IGP Link Weight Optimization in Presence of Route Reflectors. IEEE INFOCOM 2009. IEEE.
Peer reviewed
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 ...
François, J.-M., & Leduc, G. (2009). Routing Based on Delivery Distributions in Predictable Disruption Tolerant Networks. Ad hoc Networks, 7(1), 219-229.
Peer reviewed (verified by ORBi)
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 ...
Martin, S., & Leduc, G. (2009). Interpreted Active Packets for Ephemeral State Processing Routers. Lecture Notes in Computer Science, 4388, 156-167.
Peer reviewed
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 ...
Cantin, F., Gueye, C. A. B., Kaafar, M. A., & Leduc, G. (2008, December). Overlay Routing using Coordinate Systems. Poster session presented at ACM CoNext 2008 - Student Workshop, Madrid, Spain.
Peer reviewed
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 ...
Cantin, F., Gueye, C. A. B., Kaafar, M. A., & Leduc, G. (2008). A Self-Organized clustering scheme for overlay networks. Lecture Notes in Computer Science, 5343, 59-70.
Peer reviewed
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 ...
Balon, S., Delcourt, O., Lepropre, J., Skivée, F., & Leduc, G. (2008). TOTEM(v3.2) - Toolbox of Traffic Engineering Methods.
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 ...
Balon, S., & Leduc, G. (2008). Combined Intra- and Inter-domain Traffic Engineering using Hot-Potato Aware Link Weights Optimization. ACM SIGMETRICS Performance Evaluation Review, 36(1), 441-442.
Peer reviewed
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 ...
Calomme, S., & Leduc, G. (2008). An overlay maintenance protocol for overlay routing on top of ad hoc networks. Lecture Notes in Computer Science, 4982, 48-59.
Peer reviewed
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 ...
Kaafar, M. A., Gueye, C. A. B., Cantin, F., Leduc, G., & Mathy, L. (2008). Towards a Two-Tier Internet coordinate system to mitigate the impact of Triangle Inequality Violations. Lecture Notes in Computer Science, 4982, 397-408.
Peer reviewed
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 ...
Cantin, F., Gueye, C. A. B., Kaafar, M. A., Leduc, G., & Mathy, L. (2008). Explication et réduction de l’impact des violations d’inégalités triangulaires dans Vivaldi. CFIP'2008. HAL INRIA.
Peer reviewed
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 ...
Balon, S., & Leduc, G. (2007). Can Forwarding Loops Appear when Activating iBGP Multipath Load Sharing? Lecture Notes in Computer Science, 4866, 213-225.
Peer reviewed
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 ...
Calomme, S., & Leduc, G. (2007). Efficient and Resilient Overlay Topologies over Ad Hoc Networks. Lecture Notes in Computer Science, 4725, 44-58.
Peer reviewed
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 ...
El Khayat, I., Geurts, P., & Leduc, G. (2007). Machine-learnt versus analytical models of TCP throughput. Computer Networks, 51(10), 2631-2644.
Peer reviewed (verified by ORBi)
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 ...
Balon, S., Lepropre, J., Delcourt, O., Skivée, F., & Leduc, G. (2007). Traffic Engineering an Operational Network with the TOTEM Toolbox. IEEE Transactions on Network and Service Management, 4(1), 51-61.
Peer reviewed
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 ...
Jelger, C., Tschudin, C., Schmid, S., & Leduc, G. (2007). Basic Abstractions for an Autonomic Network Architecture. First IEEE Workshop on Autonomic and Opportunistic Communications (pp. 1-6). IEEE.
Peer reviewed
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 ...
François, J.-M., & Leduc, G. (2007). AP and MN-centric Mobility Prediction: A Comparative Study Based On Wireless Traces. Lecture Notes in Computer Science, 4479, 322-332.
Peer reviewed
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 ...
François, J.-M., & Leduc, G. (2007). Delivery Guarantees In Predictable Disruption Tolerant Networks. Lecture Notes in Computer Science, 4479, 167-178.
Peer reviewed
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 ...
Martin, S., & Leduc, G. (2007). Ephemeral State Assisted Discovery of Peer-to-peer Networks. In R., Boutaba, M., Brunner, & S., Schmid (Eds.), 1st IEEE Workshop on Autonomic Communications and Network Management (pp. 9-16).
Peer reviewed
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 ...
François, J.-M., & Leduc, G. (2006). Predictable disruption tolerant networks and delivery guarantees (arXiv:0612034).
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 ...
Lepropre, J., & Leduc, G. (2006, December). Inferring Groups of Correlated Failures. Poster session presented at CoNext 2006 - Student Workshop, Lisbon, Portugal.
Peer reviewed
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 ...
Balon, S., Mélon, L., & Leduc, G. (2006). A scalable and decentralized fast-rerouting scheme with efficient bandwidth sharing. Computer Networks, 50(16), 3043-3063.
Peer reviewed (verified by ORBi)
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 ...
Calomme, S., & Leduc, G. (2006). Conception d'un protocole de contrôle de topologie pour les overlays construits sur des réseaux ad hoc. CFIP'2006. HAL INRIA.
Peer reviewed
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 ...
François, J.-M., & Leduc, G. (2006). Prédiction de mobilité par le mobile ou par le point d'accès: comparaison sur base de traces réelles. CFIP'2006. HAL INRIA.
Peer reviewed
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 ...
Balon, S., & Leduc, G. (2006). Dividing the Traffic Matrix to Approach Optimal Traffic Engineering. 14th IEEE International Conference on Networks (pp. 1-6). IEEE.
Peer reviewed
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 ...
Skivée, F., Balon, S., & Leduc, G. (2006). A scalable heuristic for hybrid IGP/MPLS traffic engineering - Case study on an operational network. 14th IEEE International Conference on Networks (pp. 1-6). IEEE.
Peer reviewed
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 ...
Soldani, C., Verdicchio, F., Leduc, G., & Munteanu, A. (2006, August). Multiple Description Coding versus Transport Layer FEC for Resilient Video Transmission. IEEE.
Peer reviewed
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 ...
Balon, S., Skivée, F., & Leduc, G. (2006). How well do traffic engineering objective functions meet TE requirements? Lecture Notes in Computer Science, 3976, 75-86.
Peer reviewed
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 ...
El Khayat, I., Geurts, P., & Leduc, G. (2006). On the accuracy of analytical models of TCP throughput. Lecture Notes in Computer Science, 3976, 488-500.
Peer reviewed
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 ...
Lepropre, J., Balon, S., & Leduc, G. (2006, April). TOTEM: A Toolbox for Traffic Engineering Methods. Poster session presented at IEEE INFOCOM 2006, Barcelona, Spain.
Peer reviewed
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 ...
Leduc, G., Abrahamsson, H., Balon, S., Bessler, S., D'Arienzo, M., Delcourt, O., Domingo-Pascual, J., Cerav-Erbas, S., Gojmerac, I., Masip, X., Pescape, A., Quoitin, B., Romano, S., Salvadori, E., Skivée, F., Tran, H. T., Uhlig, S., & Umit, H. (2006). An open source traffic engineering toolbox. Computer Communications, 29(5), 593-610.
Peer reviewed (verified by ORBi)
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 ...
Bonmariage, N., & Leduc, G. (2006). A survey of optimal network congestion control for unicast and multicast transmission. Computer Networks, 50(3), 448-468.
Peer reviewed (verified by ORBi)
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 ...
Calomme, S., & Leduc, G. (2006). The Critical Neighbourhood Range for Asymptotic Overlay Connectivity in Ad Hoc Networks. Ad Hoc & Sensor Wireless Networks, 2(2), 169-187.
Peer reviewed (verified by ORBi)
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 ...
Balon, S., Skivée, F., & Leduc, G. (2005). Comparing traffic engineering objective functions. CoNext 2005 - Student Workshop (pp. 224-225). New York, USA: ACM.
Peer reviewed
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 ...
François, J.-M., & Leduc, G. (2005). Entropy-based knowledge spreading and application to mobility prediction. ACM International conference on Emerging Network Experiments and Technologies (pp. 10-20). New York, USA: ACM.
Peer reviewed
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 ...
Calomme, S., & Leduc, G. (2005). The Critical Neighbourhood Range for Asymptotic Overlay Connectivity in Dense Ad Hoc Networks. Challenges in Ad Hoc Networking (pp. 179-188). Boston, USA: Springer.
Peer reviewed
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 ...
El Khayat, I., Geurts, P., & Leduc, G. (2005). Improving TCP in wireless networks with an adaptive machine-learnt classifier of packet loss causes. Lecture Notes in Computer Science, 3462, 549-560.
Peer reviewed
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 ...
Martin, S., & Leduc, G. (2005). An active platform as middleware for services and communities discovery. Lecture Notes in Computer Science, 3516, 237-245.
Peer reviewed
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 ...
François, J.-M., & Leduc, G. (2005, April). Mobility prediction's influence on QoS in wireless networks: a study on a call admission algorithm. USA: IEEE.
Peer reviewed
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 ...
Skivée, F., Balon, S., Delcourt, O., Lepropre, J., & Leduc, G. (2005). Architecture d'une boîte à outils d'algorithmes d'ingénierie de trafic et application au réseau GEANT. Ingénierie des protocoles - Qualité de service, multimédia et mobilité (pp. 317-332). France: Hermès Lavoisier.
Peer reviewed
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 ...
Geurts, P., El Khayat, I., & Leduc, G. (2004, November). A Machine Learning Approach to Improve Congestion Control over Wireless Computer Networks. USA: IEEE.
Peer reviewed
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 ...
Skivée, F., & Leduc, G. (2004). A distributed algorithm for weighted max-min fairness in MPLS networks. Lecture Notes in Computer Science, 3124, 644-653.
Peer reviewed
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 ...
Ait-Hellal, O., & Leduc, G. (2004). TCP Vegas-like algorithm for layered multicast transmission. Communications in Computing (pp. 58-64). CSREA.
Peer reviewed
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 ...
Calomme, S., & Leduc, G. (2004, June). Performance Study of an Overlay Approach to Active Routing in Ad Hoc Networks.
Peer reviewed
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 ...
François, J.-M., Leduc, G., & Martin, S. (2004). Learning movement patterns in mobile networks: a generic method. European Wireless 2004 (pp. 128-134).
Peer reviewed
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 ...
Martin, S., & Leduc, G. (2004). A dynamic neighbourhood discovery protocol for active overlay networks. Lecture Notes in Computer Science, 2982, 151-162.
Peer reviewed
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 ...
Blanchy, F., Mélon, L., & Leduc, G. (2003). A preemption-aware on-line routing algorithm for MPLS networks. Telecommunication Systems, 24(2-4, OCT-DEC), 187-206.
Peer reviewed (verified by ORBi)
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 ...
François, J.-M., Leduc, G., & Martin, S. (2003). Evaluation d'une méthode de prédiction des déplacements de terminaux dans les réseaux mobiles. Ingénierie des protocoles - Réseaux mobiles et ad hoc, qualité de service, test et validation (pp. 189-202). France: Hermès Lavoisier.
Peer reviewed
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 ...
Blanchy, F., Mélon, L., & Leduc, G. (2003). An efficient decentralized on-line traffic engineering algorithm for MPLS networks. Providing Quality of Service in Heterogeneous Environments (pp. 451-460).
Peer reviewed
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 ...
Blanchy, F., Mélon, L., & Leduc, G. (2003). Routing in a MPLS network featuring preemption mechanisms. 10th IEEE International Conference on Telecommunications (pp. 253-260). USA: IEEE.
Peer reviewed
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 ...
Mélon, L., Blanchy, F., & Leduc, G. (2003). Decentralized local backup LSP calculation with efficient bandwidth sharing. 10th IEEE International Conference on Telecommunications (pp. 929-937). USA: IEEE.
Peer reviewed
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 ...
El Khayat, I., & Leduc, G. (2003). Smoothing the TCP rate by learning the delay versus window size dependency. Lecture Notes in Computer Science, 2899, 78-90.
Peer reviewed
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 ...
Martin, S., & Leduc, G. (2002). RADAR: Ring-based adaptive discovery of active neighbour routers. Lecture Notes in Computer Science, 2546, 62-73.
Peer reviewed
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 ...
Bonmariage, N., & Leduc, G. (2002). Adaptation dynamique des débits des couches pour la transmission vidéo multipoint. In A., Obaid (Ed.), Ingénierie des protocoles - Réseaux mobiles et ad hoc, qualité de service, multimédia, ingénierie de trafic (pp. 19-34). France: Hermès Lavoisier.
Peer reviewed
The heterogeneous environment of multicast video streams naturally raises a network performance issue which can be addressed using a layered transmission scheme. A receiver is able to adapt the flow rate to ...
Mélon, L., & Leduc, G. (2002). Comparaison quantitative de différentes techniques de restauration rapide dans les réseaux IP/MPLS. In A., Obaid (Ed.), Ingénierie des protocoles - Réseaux mobiles et ad hoc, qualité de service, multimédia, ingénierie de trafic (pp. 503-517). France: Hermès Lavoisier.
Peer reviewed
This article is dealing with a quantitative comparison of different fast restoration approaches in the context of a Multi-Protocol Label Switching (MPLS) network. The objective is to analyse the general ...
Jennes, G., Leduc, G., & Tufail, M. (2002). A scheduler for relative delay service differentiation. Annales des Télécommunications = Annals of Telecommunications, 57(1-2, JAN-FEB), 83-104.
Peer reviewed (verified by ORBi)
We propose a new delay-based scheduler called as RD-VC (Relative Delay VirtualClock). Since it performs a delay-based service differentiation among flow aggregates, the quality at microflow level is the same ...
Yamamoto, L., & Leduc, G. (2001). Autonomous Reflectors over Active Networks: Towards Seamless Group Communication. The Interdisciplinary Journal of Artificial Intelligence & the Simulation of Behavious (AISBJ), 1(1), 125-146.
Peer reviewed
We present a reflector service that seeks to maintain application-level connectivity in the presence of network-level multicast failures. The service is based on the dynamic deployment of autonomous reflectors ...
Yamamoto, L., & Leduc, G. (2001, October). Building Bidirectional Multicast Trees Using Autonomous Reflectors. Poster session presented at IWAN 2001, Philadelphia, USA.
Peer reviewed
We show an active application to build bidirectional multicast trees, based on the dynamic deployment of agents on top of an active network infrastructure, and interconnected by unicast. Such trees are used to ...
El Khayat, I., & Leduc, G. (2001). A Stable and Flexible TCP-friendly congestion control protocol for layered multicast transmission. Lecture Notes in Computer Science, 2158.
Peer reviewed
We propose an improvement of our RLS (Receiver-driven Layered multicast with Synchronization points) protocol, called CIFL for “Coding-Independent Fair Layered mulaticast”, along two axes. In CIFL, each ...
Yamamoto, L., & Leduc, G. (2001, March). Autonomous Multicast Reflectors over Active Networks. Paper presented at AISB Symposium on Software Mobility, York, UK.
Peer reviewed
We present a reflector service that seeks to maintain application-level connectivity in the presence of network-level multicast failures. The service is based on the dynamic deployment of autonomous reflectors ...
Leduc, G. (2001). Multimedia in the E-LOTOS Process Algebra. Formal Methods for Distributed Processing - A Survey of Object Oriented Approaches (pp. 357-372). UK: Cambridge University Press.
We illustrate how the ISO E-LOTOS language can be used to describe an ODP multicast multimedia binding object of some complexity. The timing features of the language are briefly recalled, and play a major role ...
El Khayat, I., & Leduc, G. (2000, November 06). Contrôle de congestion pour la transmission multipoint en couches. Paper presented at Journées Doctorales Informatiques et Réseaux (JDIR 2000), Paris, France.
Le contrôle de congestion en transmission multipoints est rendu difficile par l'hétérogénéité des récepteurs. En effet, pour la transmission vidéo par exemple, il serait peu raisonnable que l'émetteur adapte ...
Yamamoto, L., & Leduc, G. (2000). An Active Layered Multicast Adaptation Protocol. Lecture Notes in Computer Science, 1942, 180-194.
Peer reviewed
We describe an active application in the field of multicast congestion control for real-time traffic. Our Active Layered Multicast Adaptation Protocol is a layered multicast congestion control scheme built on ...
Jennes, G., Leduc, G., & Tufail, M. (2000). Un ordonnanceur assurant des services différenciés relatifs basés sur le délai. In J.-P., Courtiat, M., Diaz, & P., Sénac (Eds.), Qualité de Service, multimédia et mobilité (pp. 97-112). France: Hermès.
Peer reviewed
Nous proposons l'ordonnanceur RD-VC garantissant des services différenciés (DiffServ) relativement quantifiés basés sur le délai. Un tel ordonnanceur assure que différentes classes de service obtiennent des ...
Yamamoto, L., & Leduc, G. (2000). Adaptive Applications over Active Networks: Case Study on Layered Multicast. IP Networks Versus conventional Switched Networks (pp. 386-394). USA: IEEE Press.
Peer reviewed
In this paper we study the potential and limitations of active networks in the context of adaptive applications. We present a survey of active networking research applied to adaptive applications, and a case ...
Yamamoto, L., & Leduc, G. (2000). An agent-inspired active network resource trading model applied to congestion control. Lecture Notes in Computer Science, 1931, 151-169.
Peer reviewed
In order to accommodate fluctuations in network conditions, adaptive applications need to obtain information about resource availability, Using active networks, new models for adaptive applications can be ...
Leduc, G., & Germeau, F. (2000). Verification of security protocols using LOTOS-method and application. Computer Communications, 23(12), 1089-1103.
Peer reviewed (verified by ORBi)
We explain how the formal language LOTOS can be used to specify security protocols and cryptographic operations. We describe how security properties can be modelled as safety properties and how a model-based ...
Leduc, G. (2000). Verification of two versions of the challenge handshake authentication protocol (CHAP). Annales des Télécommunications = Annals of Telecommunications, 55(1-2), 20-30.
Peer reviewed (verified by ORBi)
The challenge handshake authentication protocol, CHAP, is an authentication protocol intended for use primarily by hosts and routers that connect to a network server I in switched circuits or dial-up lines ...
El Khayat, I., & Leduc, G. (2000). Congestion Control for Layered Multicast Transmission. Networking and Information Systems Journal, 3(3-4), 559-573.
Peer reviewed
Heterogeneity of receivers makes it hard to control congestion for multicast transmission. Using hierarchical layering of the information is one of the most elegant and efficient approach to tackle this ...
Yamamoto, L., & Leduc, G. (2000). Resource Trading Agents for Adaptive Active Network Applications. Networking and Information Systems Journal, 3(4-5), 743-768.
Peer reviewed
Adaptive applications seem to be the only realistic answer to the increasing diversity and decentralisation in networks. In order to accommodate fluctuations in network conditions, adaptive applications need ...
Ait-Hellal, O., Yamamoto, L., & Leduc, G. (1999). Cycle-based TCP-Friendly Algorithm. Proceedings of IEEE Globecom'99 (pp. 776-780). USA: IEEE Press.
Peer reviewed
Several TCP-Friendly algorithms have been recently proposed to support multimedia applications. These algorithms try to mimic the congestion control behavior of TCP. However, the oscillatory (bursty) nature of ...
Tufail, M., Jennes, G., & Leduc, G. (1999). A scheduler for delay-based service differentiation among AF classes. In D., Tsang & P., Kühn (Eds.), Broadband Communications - Convergence of Network Technologies (pp. 93-102). USA: Kluwer Academic Press.
Peer reviewed
In the Differentiated Services (DS) framework, service differentiation is performed among the aggregates (collection of one or more microflows) rather than among the microflows (data stream pertaining to a ...
Tufail, M., Jennes, G., & Leduc, G. (1999). Attaining per flow QoS with Class-based Differentiated Services. In R., Onvural, S., Civanlar, & J., Luciani (Eds.), Internet II: Quality of Service and Future Directions (pp. 101-112). USA: International Society for Optical Engineering.
Peer reviewed
The Differentiated Services (DiffServ or DS) framework takes an edge over IntServ because it is scalable and lesser complex. On the other hand, the application level end-to-end quality o f service, in DiffServ ...
Rosolen, V., Bonaventure, O., & Leduc, G. (1999). A RED discard strategy for ATM networks and its performance evaluation with TCP/IP Traffic. Computer Communication Review, 29(3), 23-43.
Peer reviewed (verified by ORBi)
In ATM UBR networks supporting TCP traffic, optimal efficiency can only be envisaged if switches adopt a discard mechanism that operates at the packet level rather than the cell level. In this paper, we define ...
Leduc, G., Bonaventure, O., Koerner, E., Léonard, L., & Pecheur, C. (1999). Model-based verification of a security protocol for conditional access to services. Formal Methods In System Design, 14(2), 171-191.
Peer reviewed (verified by ORBi)
We use the formal language LOTOS to specify and verify the robustness of the Equicrypt protocol under design in the European OKAPI project for conditional access to multimedia services. We state some desired ...
Rosolen, V., Bonaventure, O., & Leduc, G. (1998). Impact of cell discard strategies on TCP/IP in ATM UBR networks. Performance Modelling and Evaluation of ATM Networks. USA: Kluwer Academic Press.
Peer reviewed
In ATM UBR networks supporting TCP traffic, optimal efficiency can only be envisaged if switches adopt a discard mechanism that operates at the packet level rather than the cell level. In this paper, we ...
Léonard, L., & Leduc, G. (1998). A formal definition of time in LOTOS (Full version). Formal Aspects of Computing, 10E, 28-96.
Peer reviewed (verified by ORBi)
Enhanced Timed-LOTOS, denoted ET-LOTOS, is an extension of LOTOS that allows the modelling of real-time behaviours. It covers all the aspects of full LOTOS, including data types, it supports both a dense and a ...
Léonard, L., & Leduc, G. (1998). A formal definition of time in LOTOS. Formal Aspects of Computing, 10(3), 248-266.
Peer reviewed (verified by ORBi)
Enhanced Timed-LOTOS, denoted ET-LOTOS, is an extension of LOTOS that allows the modelling of real-time behaviours. It covers all the aspects of full LOTOS, including data types, it supports both a dense and a ...
Germeau, F., & Leduc, G. (1997). A Computer Aided Design of a Secure Registration Protocol. Formal Description Techniques and Protocol Specification, Testing and Verification. Chapman and Hall.
Peer reviewed
We use the formal language LOTOS to specify a registration protocol between a user and a Trusted Third Party, that requires mutual authentication. We explain how a model-based verification method can be used ...
Germeau, F., & Leduc, G. (1997). Model-based Design and Verification of Security Protocols using LOTOS. Design and Formal Verification of Security Protocols.
Peer reviewed
We explain how the formal language LOTOS can be used to specify security protocols and cryptographic operations. We describe how to model security properties as safety properties and how a model-based ...
Février, A., Najm, E., Leduc, G., & Léonard, L. (1997). QoS specification of ODP binding objects. Telektronikk, 93(1), 42-49.
We present a QoS oriented notation suitable for the ODP framework. In particular, we focus on a computational view of objects: we consider systems described as configurations of interacting objects and we deal ...
Léonard, L., & Leduc, G. (1997). An introduction to ET-LOTOS for the description of time-sensitive systems. Computer Networks & ISDN Systems, 29(3), 271-292.
Peer reviewed (verified by ORBi)
Enhanced Timed-LOTOS, called ET-LOTOS, is an extension of LOTOS allowing the modelling of time-sensitive systems (i.e. systems whose behaviour is influenced by the passing of time). It is the basis of the ...
Leduc, G., Bonaventure, O., Koerner, E., Léonard, L., Pecheur, C., & Zanetti, D. (1996). Specification and verification of a TTP protocol for the conditional access to services. Formal Methods and their Applications: Telecommunications, VLSI and Real-Time Computerized Control Systems.
Peer reviewed
We use the formal language LOTOS to specify the Equicrypt protocol and verify its robustness to attacks by an intruder. We use the model-based CADP verification tools from the Eucalyptus toolbox to discover ...
Février, A., Najm, E., Leduc, G., & Léonard, L. (1996). Compositional Specification of ODP Binding Objects. Information Network and Data Communication.
Peer reviewed
A building blocks approach for the formal specification of binding objects in the ODP Computational Model is presented. The formal notation that is used is based on LOTOS extended with two features - real time ...
Mathy, L., Leduc, G., Danthine, A., & Bonaventure, O. (1996, March). Towards an Integrated Solution for Multimedia Communications. Bulletin Scientifique de l'Association des Ingénieurs Electriciens sortis de l'Institut Electrotechnique Montefiore.
During the last few years, we have been witnessing tremendous changes in the communication environment. Those changes are not only due to the availability of higher data rates in the communication networks but ...
Léonard, L., & Leduc, G. (1995). An Extended LOTOS for the design of Real-Time Systems. Design and Analysis of Real Time Systems.
We give a brief presentation of ET-LOTOS. ET-LOTOS extends with quantative time the formal description technique LOTOS. ET-LOTOS serves as basis for the time extension part of E-LOTOS, the new standard for ...
Leduc, G. (1994). Failure-based Congruences, Unfair Divergences and New Testing Theory. In S., Vuong & S., Chanson (Eds.), Protocol Specification, Testing and Verification, XIV (pp. 252-267). London, UK: Chapman & Hall.
Peer reviewed
The testing equivalence 'te' that is used as a reference in verification and testing theory in LOTOS is not a congruence, and no explicit definition of the least congruence stronger than 'te' has been found ...
Mathy, L., Leduc, G., Bonaventure, O., & Danthine, A. (1994). A Group Communication Framework. In W., Bauerfeld, O., Spaniol, & F., Williams (Eds.), Broadband Islands '94: Connecting with the End-User (pp. 167-178). Elsevier Science.
Peer reviewed
This paper presents a general architectural model for group communications which are communications that may involve more than two parties. The concept of group is presented and the concept of group ...
Baguette, Y., & Leduc, G. (1994). The Connection Release Facilities in the OSI95 Transport Service. The OSI95 Transport Service with Multimedia Support (pp. 199-211). Springer.
We explain in detail how the work carried out on the transport connection release aspects in the framework of the OSI95 Connection-Mode Transport Service has led to the introduction of a graceful transport ...
Baguette, Y., Léonard, L., Leduc, G., & Danthine, A. (1994). The OSI95 Connection-Mode Transport Service. The OSI95 Transport Service with Multimedia Support (pp. 181-198). Springer.
We present the main features of the connection-mode service developed as a part of the entire OSI95 Enhanced Transport Service. This connection-mode service results from modifications and enhancements to the ...
Danthine, A., Bonaventure, O., & Leduc, G. (1994). The Qos Enhancements in OSI95. The OSI95 Transport Service with Multimedia Support (pp. 125-150). Springer.
The new communication environment has brought new requirements on the qualities of service for which the present "best effort" semantics is inadequate. The response to this evolution goes through the ...
Leduc, G. (1994). A Method for Applying LOTOS at an Early Design Stage and Its Application to the ISO Transport Protocol. The OSI95 Transport Service with Multimedia Support (pp. 151-180). Springer.
We propose a method applicable to the design of large and abstract LOTOS specifications. More precisely, this method explains how to generate a constrain-oriented specification which is an adequate abstract ...
Leduc, G., & Danthine, A. (1994). On the Provision of a Fast Connect Facility in a Connection-Mode Transport Service. The OSI95 Transport Service with Multimedia Support (pp. 225-238). Springer.
A "fast connect" facility in a connection-mode service allows the calling service user to send service data units without waiting for the rount trip delay associated with the successful establishment of the ...
Leduc, G., & Danthine, A. (1994). OSI95 Contributions to ISO/IEC and ETSI. The OSI95 Transport Service with Multimedia Support (pp. 378-387). Springer.
This paper summarizes the activities that were carried out within the standardization bodies ISO/IEC and ETSI during the two-year period of the OSI95 project. However it focuses mainly on the OSI95 contributions.
Léonard, L., Leduc, G., & Danthine, A. (1994). The Tick-Tock Case Study for the Assessment of Timed FDT's. The OSI95 Transport Service with Multimedia Support (pp. 338-352). Springer.
The initial purpose of this paper was to design a case study to assess LOTOS-T [MFV93] which is a temporal extension of LOTOS developed within the ESPRIT II OSI95 project. However, we think that it can be ...
Léonard, L., & Leduc, G. (1993). An Enhanced Version of Timed LOTOS and its Application to a Case study. In R. L., Tenney, P. D., Amer, & M. U., Uyar (Eds.), FORMAL DESCRIPTION TECHNIQUES, VI (pp. 483-498). Elsevier Science.
Peer reviewed
We propose here ET-LOTOS, a timed extension of LOTOS. It is an enhancement of Timed LOTOS that we presented at FORTE 92. We show how some simple modifications allow us to improve the expressiveness of our ...
Leduc, G., & Léonard, L. (1993). Comment rendre LOTOS apte à spécifier des systèmes temps réel ? In R., Dssouli & G., Bochmann (Eds.), Ingénierie des Protocoles (pp. 407-425). Paris, France: Hermès.
We explain and justify by examples our proposed timed extension of LOTOS. The examples cover protocol functions and service facilities that are frequently encountered in practice or are inspired by existing ...
Danthine, A., Baguette, Y., Leduc, G., & Léonard, L. (1992). The OSI 95 Connection-mode Transport Service-The Enhanced QoS. In A., Danthine & O., Spaniol (Eds.), HIGH PERFORMANCE NETWORKING, IV (pp. 235-252). Elsevier Science.
Peer reviewed
During the last ten years, tremendous changes have taken place in the communication environments. First, there has been a continuous increase in network performance that has led, for instance, to increasingly ...
Leduc, G., & Léonard, L. (1992). A Timed LOTOS Supporting a Dense Time Domain and Including New Timed Operators. In M., Diaz & R., Groz (Eds.), Formal Description Techniques V (pp. 87-102). Elsevier Science.
Peer reviewed
A time extended version of LOTOS, denoted Timed LOTOS, is proposed for the modelling of quantitative timed behaviours. In this language neither the syntax nor the semantics are restricted to a specific time ...
Leduc, G. (1992). A Framework Based on Implementation Relations for Implementing LOTOS Specifications. Computer Networks & ISDN Systems, 25(1), 23-41.
Peer reviewed (verified by ORBi)
A framework is developed for studying the implementation process, as a stepwise process in which an abstract specification is successively transformed to reach a final compilable specification adapted to the ...
Leduc, G. (1992). An Upward Compatible Timed Extension to LOTOS. In K., Parther & G., Rose (Eds.), Formal Description Techniques IV (pp. 217-232). Elsevier Science.
Peer reviewed
We propose a timed extension of LOTOS, denoted TLOTOS, which is upward compatible with the standard LOTOS. It means first that a timed behaviour expression which does not use any language extension will have ...
Lallemand, E., & Leduc, G. (1991). A LOTOS Data Facility Compiler (DAFY). In K., Parther & G., Rose (Eds.), Formal Description Techniques IV (pp. 313-327). Elsevier Science.
Peer reviewed
If we take a look at existing LOTOS specifications, we notice that the description of the needed data types is very often huge. This causes the lack of concision of most descriptions of complex systems. We ...
Leduc, G. (1991). Conformance relation, associated equivalence, and minimum canonical tester in LOTOS. In B., Jonsson, J., Parrow, & B., Pehrson (Eds.), Protocol Specification, Testing, and Verification, XI (pp. 249-264). Elsevier Science.
Peer reviewed
We first study the conf relation proposed by E. Brinksma and G. Scollo to formalise testing conformance. It is well-known from their work that, in order to test whether an implementation of a specification S ...