Design and performance evaluation of a state-space based AQM

Recent research has shown the link between congestion control in communication networks and feedback control system. In this paper, the design of an active queue management (AQM) which can be viewed as a controller, is considered. Based on a state space representation of a linearized fluid flow model of TCP, the AQM design is converted to a state feedback synthesis problem for time delay systems. Finally, an example extracted from the literature and simulations via a network simulator NS (under cross traffic conditions) support our study

Robust control tools for traffic monitoring in TCP/AQM networks

Several studies have considered control theory tools for traffic control in communication networks, as for example the congestion control issue in IP (Internet Protocol) routers. In this paper, we propose to design a linear observer for time-delay systems to address the traffic monitoring issue in TCP/AQM (Transmission Control Protocol/Active Queue Management) networks. Due to several propagation delays and the queueing delay, the set TCP/AQM is modeled as a multiple delayed system of a particular form. Hence, appropriate robust control tools as quadratic separation are adopted to construct a delay dependent observer for TCP flows estimation. Note that, the developed mechanism enables also the anomaly detection issue for a class of DoS (Denial of Service) attacks. At last, simulations via the network simulator NS-2 and an emulation experiment validate the proposed methodology

On Designing Lyapunov-Krasovskii Based AQM for Routers Supporting TCP Flows

For the last few years, we assist to a growing interest of designing AQM (Active Queue Management) using control theory. In this paper, we focus on the synthesis of an AQM based on the Lyapunov theory for time delay systems. With the help of a recently developed Lyapunov-Krasovskii functional and using a state space representation of a linearized fluid model of TCP, two robust AQMs stabilizing the TCP model are constructed. Notice that our results are constructive and the synthesis problem is reduced to a convex optimization scheme expressed in terms of linear matrix inequalities (LMIs). Finally, an example extracted from the literature and simulations via {\it NS simulator} support our study

Multiple time-delays system modeling and control for router management

Abstract-This paper investigates the overload problem of a single congested router in TCP (Transmission Control Protocol) networks. To cope with the congestion phenomenon, we design a feedback control based on a multiple time-delays model of the set TCP/AQM (Active Queue Management). Indeed, using robust control tools, especially in the quadratic separation framework, the TCP/AQM model is rewritten as an interconnected system and a structured state feedback is constructed to stabilize the network variables. Finally, we illustrate the proposed methodology with a numerical example and simulations using NS-2 [1] simulator

Sur la stabilité des systèmes à retards variant dans le temps: théorie et application au contrôle de congestion d'un routeur

This thesis investigates the existing links between the control theory and the communication networks supporting the well-known communication protocol TCP. The key idea consists in using the tools from control theory for the network traffic stabilization. First, we have addressed the stability analysis of time-varying delay systems via two temporal approaches. On one hand, we consider the well-known Lyapunov-Krasovskii method in which new functionals are built according to original modelings of the system (delay fractionning , system derivative). On the other hand, the stability is also assessed with an input-output approach, borrowing then tools from the robust control framework. The time delay system is then rewritten as the interconnection of a linear application with a matrix consisting in a set of operators that defines the former system. Thus, having revisited the quadratic separation principle, additional auxiliary operators are proposed in order to provide an enhanced modeling of the delayed dynamic. In a second part, the developed methodology is used to cope with the congestion phenomenon in a router supporting TCP communications. This end-to-end protocol is sensitive to packet losses and adjusts thereof its sending rate with respect to the AIMD (Additive-Increase Multiplicative-Decrease) algorithm. Based on the Active Queue Management (AQM) principle, we design a controller embedded into the router that monitors the packet losses. A such mechanism allows to stabilize the network traffic and to control the congestion phenomenon in spite of the delays induced by the network. All theoretical results are tested through experiments under the network simulator NS-2.Cette thèse s'inscrit dans une thématique pluridisciplinaire explorant les liens existants entre la théorie de la commande et les réseaux informatiques. L'idée consiste à appliquer les outils de l'Automatique pour la stabilisation du trafic dans les réseaux de communication. Premièrement, nous nous sommes intéressés à l'analyse de stabilité des systèmes à retards variables au travers de deux approches temporelles. D'une part, nous avons considéré la méthode de Lyapunov-Krasovskii dans laquelle nous avons élaboré des fonctionnelles en adéquation avec de nouvelles modélisations du système (segmentation du retard, dérivée temporelle). D'autre part, la stabilité a également été abordée avec une approche entrée-sortie, empruntant alors les outils de l'analyse robuste. Le système à retard est alors réécrit comme l'interconnexion d'une application linéaire avec une matrice constituée d'opérateurs définissant le système original. Après avoir revisité le principe de séparation quadratique, nous développons des opérateurs auxiliaires afin de caractériser au mieux la dynamique retardée et proposer des critères moins pessimistes. Deuxièmement, la méthodologie développée est ensuite utilisée pour le problème de contrôle de congestion d'un routeur lors de communications TCP. Ce protocole de bout en bout est sensible à la perte de paquet et modifie en conséquence son taux d'émission selon l'algorithme du AIMD. Il s'agit alors de commander le taux de perte par l'intermédiaire d'un mécanisme d'Active Queue Management situé au niveau du routeur afin de réguler le trafic. Les résultats théoriques sont ensuite évalués à l'aide du simulateur de réseaux NS-2

A singular perturbation approach for the control of electromagnetic actuators

International audienceThe paper is devoted to the control of electromagnetic actuators. Compared to most results in the literature, the design explicitly takes into account the nonlinearities and the magnetic saturation. An approach based on singularly perturbed systems is proposed to take advantage of the different time scales of the model and provide a minimal complexity control law. Associated with an integral action, this control law ensures accuracy and robustness w.r.t some disturbances and some unknown parameters of the actuator. The use of the singular perturbation method allows also to limit the implementation complexity compared to classical methods such as backstepping control. The synthesis of the control law is then tested through simulations that illustrate the efficiency of the method

Delay Range Stability of distributed time delay systems

International audienceThis paper is dedicated to the stability analysis of a class of uncer- tain distributed delay systems. We focus to the case where the kernel can be modelled as a polynomial function. The results are constructed by rewriting the system as an uncertain interconnected model and appropri- ate robust control tools as quadratic separation are then used to address to stability issue. Furthermore, some relations that highlight features of the delayed term are added to the interconnected model leading then to the conservatism reduction. At last, stability conditions are expressed in terms of LMIs which can be solved efficiently. Finally, some numerical examples show the effectiveness the proposed method

Construction of Lyapunov-Krasovskii functional for time-varying delay systems

International audienceThis paper provides some new techniques to construct a Lyapunov-Krasovskii functional for time varying delay systems. The construction is based on a partitioning scheme of the time-varying delay leading to a new type of Lyapunov-Krasovskii functional. This functional is depending on an augmented state and also on an integral quadratic constraint added to reduce the conservatism of the proposed methodology. This approach is then extended to the robust case. Finally, some examples support our approach

Input-output framework for robust stability of time-varying delay systems

International audienceThe paper is devoted to the stability analysis of linear time varying delay. We first model the time varying delay system as an interconnected system between a known linear transformation and some operators depending explicitly on the delay. Embedding operators related to the delay into an uncertain set, stability of such system is then performed by adopting the quadratic separation approach. Having recognized that the conservatism comes from the choice of the feedback modeling and the operators definition, these first results are afterwards enhanced by using some redundant equation and scaling filter. At last, numerical examples are given to illustrate the results