Belhassen Zouari

Nodes self-scheduling approach for maximising wireless sensor network lifetime based on remaining energy

Coverage and energy conservation are two major issues in wireless sensor networks (WSNs), especially when sensors are randomly deployed in large areas. In such WSNs, sensors are equipped with limited lifetime batteries and redundantly cover the target area. To face the short lifetime of the WSN, the objective is to optimise energy consumption while maintaining the full sensing coverage. A major technique to save the energy is to use a wake-up scheduling protocol through which some nodes stay active whereas the others enter sleep state so as to conserve their energy. This study presents an original algorithm for node selfscheduling to decide which ones have to switch to the sleep state. The novelty is to take into account the remaining energy at every node in the decision of turning off redundant nodes. Hence, the node with a low remaining energy has priority over its neighbours to enter sleep state. The decision is based on a local neighbourhood knowledge that minimises the algorithm overhead. To verify and evaluate the proposed algorithm, simulations have been conducted and have shown that it can contribute to extend the network lifetime. A comparison with existing works is also presented and the performance gains are highlighted.

Synthesis of controllers using coloured petri nets and theory of regions

Abstract This paper addresses the forbidden state control problem of discrete event systems using coloured Petri nets. The problem is studied in the general framework of Ramadge and Wonham theory considering uncontrollable transitions and under non-blockingness requirement. The synthesis method computes a maximally permissive coloured Petri net controller. First, the legal behaviour the plant model should have is determined. Then, the theory of regions is applied in order to generate a maximally permissive controller. This controller is expressed in coloured Petri net terms and, is connected to the plant model. The proposed approach exploits the benefits of the parameterised modelling power of coloured Petri nets at the specification level of the plant model as well as at the synthesis level.

Shortest Path Search in Dynamic Reliability Space: Hierarchical Coloured Petri Nets Model and Application to a Pipeline Network

His work proposes a hierarchical Coloured Petri Nets (CPN) model for finding the most reliable path in an oil pipeline network. A path is achieved with the opening of valves along it linking the pipes and with the closing of the adjacent ones to isolate it from the rest of the pipeline network. This work has two goals: firstly to calculate the dynamic reliability of the valves engaged to open (openers) and to close (closers) in the paths search according to their behavior, and secondly to find an optimal path in the reliability space using Dijkstras algorithm. Real operational constraints and goals in the seaport are modeled with data extracted from OREDA Database. The results underline how the proposed solution leads to a safer use of the network by avoiding the riskiest valves.

Supervisory Control and High-level Petri nets

The Supervisory Control Theory (SCT) (RamadgeW Giua & DiCesare, 1994; Sreenivas & Sreenivas, 1997), since they represent a good trade-off between modelling power and analysis capabilities. For details about the supervisory control problem methods based on Petri nets, one can refer to (Holloway et al., 1997; Su et al., 2005). In addition, high level nets, especially Coloured Petri nets (CP-nets) (Jensen & Rozenberg, 1991), provide a great improvement over the ordinary Petri nets. Notably, the high expressiveness of CP-nets allows to obtain compact models even for large systems, while keeping the same formal analysis capabilities. However, not many works have addressed the supervisory control problem by considering a CP-net as a plant model. In this context, we can cite the method developed in (Makungu et al., 1999). This method addresses the forbidden state problem for a class of CP-nets where the process to be controlled is separated from the control logic. In this chapter, we review our previous works (Abid & Zouari, 2008; Zouari & Ghedira, 2004; Zouari & Zairi, 2005) for the supervisory control problem of DES modelled by CP-nets. The control specifications herein considered are expressed in terms of forbidden states, i.e. states which have to be avoided by the controlled model. In a first approach, we propose to derive a controller for a plant CP-net model by using the theory of regions. According to the control specifications, the desired behaviours are extracted from the rechability graph associated with the plant model. Then, the theory of regions is used in order to design the controller. Thanks to the expressiveness of CP-nets, as a main advantage, the obtained controller is reduced to one single place. Secondly, we propose to optimise the first approach in order to deal efficiently with symmetric systems. Indeed, the reachability graph of a symmetric system can be represented by an optimised version, called symbolic reachability graph (Chiola et al., 1991; 1997), which is quite smaller. Thereby, the use of symbolic graphs allows to alleviate one important drawback of the latter approach which is the well-known problem of the state space explosion. Moreover and consequently, the use of a smaller graph allows to reduce the complexity of the synthesis process. Finally, we propose an approach which considers as plant model a CP-net that is assumed to be structured on a set of generic processes sharing a set

Synthesis of controllers for symmetric systems

This article deals with supervisory control problem for coloured Petri (CP) nets. Considering a CP-net, we build a condensed version of the ordinary state-space, namely the symbolic reachability graph (SRG). This latter graph allows to cope with state-space explosion problem for symmetric systems. The control specification can be expressed in terms of either forbidden states or forbidden sequences of transitions. According to these specifications, we derive the controller by applying the theory of regions on the basis of the SRG. Thanks to expressiveness power of CP-nets, the obtained controller to be connected to the plant model is reduced to one single place.

A Distributed and Coordinated Massive DDOS Attack Detection and Response Approach

Nowadays Distributed Denial of Service (DDoS) attacks related to networked enterprise systems is a problem that has become much known. Many papers dealt with this type of attacks. Recently DDoS attacks that target large cyberspaces like national cyberspaces have become a hot topic. We start from an existing architecture called Saher Architecture. Saher is used to detect attacks threatening Tunisian National cyberspace. We improve this architecture and propose an approach that allows using a consensus algorithm executed by the probes of the Internet Service Providers in order to detect and react to massive DDoS attacks in a coordinated fashion and under Byzantine assumptions. Different levels of alerts are proposed and the reaction mechanisms depend on the type of the attack. The final outcome of this research is a framework that affords the necessary mechanisms allowing a national cyberspace to counter massive DDoS attacks by coordinating internet Service Providers effort in order to detect and respond to the attacks.

Global generic model for formal validation of the wireless sensor networks properties

Abstract Formal modelling techniques can be used for the analysis of wireless sensor networks (WSNs). High level Petri nets (HLP-nets) that is an extension of Petri nets is a powerful modelling technique. This paper presents a HLP-nets based approach for formal modelling and analysis of WSNs. The proposed model uses the hierarchical modelling capability of HLP-nets, including different levels of abstraction. The proposed HLP-net model is quite general and generic to present a large class of WSN behaviour. It globally models the behaviour of all the WSNs components (nodes and bases station). The designer can choose the specific level of abstraction. The interfacing of the HLP-net models representing the node operations is made through the model semantics and the fusion places (where anything that happens to each place also happens to all the other places). No additional efforts must be done to synchronise all components models. Add to the simulation possibility, formal verification of the network properties is also enabled based on the proposed HLP-net model. Such feasibility represents one of the major difference distinguishing the proposed method of all the existing simulators dedicated to WSNs.

Formal Approach for Modeling, Verification and Performance Analysis of Wireless Sensors Network

The Control of energy consumption by sensor networks and the maximization of the sensor network lifetime are the most fundamental issues. Due to the variety of protocols dedicated to the different sensor’s layers and the difficulty of a real network deployment, designers need some mechanisms and tools to validate the energy consumption and to observe its impact on the network’s lifetime before deployment. In this context, we have proposed a modeling approach considering the global behavior of a sensor network and allowing the estimation of the network’s energy consumption. This approach is based on the concept of components oriented modeling and the expressiveness of Colored Petri Nets (CP-NET). Thus, the global model representing sensor behavior is obtained by interfacing different models each one representing the behavior of a particular component of the sensor. In this work, our interest was firstly focused on the radio because it’s the most energy consumer. When observing the node functioning, we show that the radio behavior is mainly controlled by the MAC component. Therefore, we were also interested in MAC component. The generated model has been used to estimate the energy consumption and to evaluate the network lifetime. Adopting the oriented components modeling approach, we may obtain two global models, where only MAC protocol change. Obtained models, representing the behavior of mostly used MAC protocols, allow comparing the impact of these two protocols on the network’s global behavior and particularly on its lifetime.

A distributed state space for modular Petri nets

This paper deals with the modular verification of modular Petri nets. We propose a new modular structure of the state space of a given modular Petri. Such a structure associates a graph with each module of the system allowing to describe the module behaviours and some global information. Thanks to the modularity of the proposed structure, the explosion problem of the state space is attenuated. Further, the proposed structure allows to limit the verification of some generic properties that concern one module to the exploration of its associated graph.

Configuration of Sensor Networks by Energy Minimisation

Recent advances in wireless sensor networks have led to many new protocols specifically designed for sensor networks where energy awareness is an essential consideration. Attention has been mostly directed towards routing protocols. These protocols generally implement a view embracing a local energy reserve. This paper presents an algorithm for determining optimal paths connecting sensor nodes to the sink. These optimal paths contribute to minimizing intermediate hops and consider a global energy reserve. Most of these sensor networks will require application specific functionalities and performance requirements because of the wide range of their applications. Modelling sensor network behaviour before implementation and deployment is therefore crucial to programming efficiently the network application and to validating all its protocols. Existing works suffer from the problem of insufficient formal models for sensor network validations. Such models enable formal verification of all sensor network properties prior to deployment. This paper will also present a formal model representing sensor network behaviour.