Jihene Rezgui

Distributed Admission Control in Wireless Mesh Networks: Models, Algorithms, and Evaluation

Wireless mesh networks (WMNs) have attracted increasing attention from the research community as a high-performance and low-cost solution to last-mile broadband Internet access. In WMNs, admission control is deployed to efficiently control different traffic loads and prevent the network from being overloaded. This paper introduces a distributed admission control scheme for WMNs, namely, routing on cliques admission control (RCAC). In particular, we propose an analytical model to compute the appropriate acceptance ratio and guarantee that the packet loss probability (PLP) in the network does not exceed a threshold value. The model also allows computing end-to-end delay to process flow requests with delay constraints. RCAC achieves scalability since it partitions the network into cliques, and only clique heads (CHs) are involved in the admission-control procedure. Using extensive simulations, we demonstrate that our RCAC achieves high resource utilization by providing lower blocking probabilities in a dynamic traffic-load environment while satisfying quality-of-service (QoS) constraints in terms of PLP and end-to-end delay. Moreover, we show that a contention access (CA) enforced with our RCAC outperforms the mesh deterministic access (MDA).

Deterministic access for DSRC/802.11p vehicular safety communication

In this work, we present the design of an efficient Deterministic medium Access (DA) for Dedicated Short-Range Communication (DSRC) vehicular safety communication over IEEE 802.11p, called Vehicular DA (VDA). VDA supports two types of safety services (emergency and routine safety messages) with different priorities and strict requirements on delay, especially for emergency safety messages. VDA processes both types of safety messages to maintain a balance between two conflicting requirements: reducing chances of packets collisions and lowering the transmission delay. To avoid long delays and high packets collisions, VDA allows vehicles to access the wireless medium at selected times with a lower contention than would otherwise be possible within two-hop neighborhood by the classical 802.11p EDCA or DCF schemes. Particularly, our scheme provides an efficient adaptive adjustment of the Contention Free Period (CFP) duration to establish a priority between emergency and routine messages. Simulations show that the proposed scheme clearly outperforms the classical DCF scheme used by 802.11p in high-offered load conditions while bounding the transmission delay of safety messages.

Detecting faulty and malicious vehicles using rule-based communications data mining

The reliability of most safety applications that are based on vehicular communications, depends in turn on the reliability of data received by each vehicle from its neighbors. Routine messages exchanged in Vehicular Ad hoc Networks (VANETs) include crucial information for safety applications such as direction, position, etc. A vehicle failure and/or a malicious vehicle transmitting false information may affect the data collection scheme and cause a disturbance for safety applications. In such a scenario, (1) the faulty/malicious vehicle should be detected rapidly and (2) routine messages exchange should be updated in consequence. To be able to detect the faulty/malicious vehicle, we developed a mechanism that collects, at a single vehicle, data regarding each neighbour transmission, and extracts the temporal correlation rules between vehicles implicated in transmissions in the neighbourhood. With the mechanism, called VANETs Association Rules Mining (VARM), a mining process will take place during a-priori constant historical period. The associations rules formulated during the mining process will be used to detect a faulty or malicious vehicle, i.e., a vehicle which is not correlated with vehicles in the neighbourhood following these rules. To react after this kind of anomaly detection, an 1:N technique is used as a protection for reestablishing the accuracy of the data collection process between vehicles communicating in the neighbourhood. Simulation results demonstrate the efficiency of the VARM scheme.

A distributed admission control scheme for Wireless Mesh Networks

Admission control is a key management function in wireless networks, particularly wireless mesh networks (WMNs), in order to support multimedia applications that require quality of service (QoS) guarantees. Even using state of the art schemes to provide QoS, if the amount of traffic in the network is allowed to increase in an uncontrolled manner, network performance will deteriorate significantly degrading the QoS for all network traffic. With admission control, a new flow is admitted only if the QoS requirements of all flows in the network still can be met after the new flow begins. This paper introduces a distributed admission control scheme, called RCAC (routing on cliques admission control) for WMNs. We propose an analytical model that enables computing the appropriate admission ratio to guarantee that the loss rate in the network does not exceed a target value; the model also allows computing end-to-end delay necessary to process flow requests with delay constraints. RCAC achieves scalability since it partitions the network into cliques; only clique heads are involved in the admission control procedure. Simulations, using ns-2, demonstrate that RCAC accepts new incoming flows only when the network target loss rate and end-to-end delay are satisfied and maintains relatively high resource utilization in a dynamic traffic load environment.

Using FCA to suggest refactorings to correct design defects

Design defects are poor design choices resulting in a hard-to-maintain software, hence their detection and correction are key steps of a disciplined software process aimed at yielding high-quality software artifacts. While modern structure- and metric-based techniques enable precise detection of design defects, the correction of the discovered defects, e.g., by means of refactorings, remains a manual, hence error-prone, activity. As many of the refactorings amount to re-distributing class members over a (possibly extended) set of classes, formal concept analysis (FCA) has been successfully applied in the past as a formal framework for refactoring exploration. Here we propose a novel approach for defect removal in object-oriented programs that combines the effectiveness of metrics with the theoretical strength of FCA. A case study of a specific defect, the Blob, drawn from the Azureus project illustrates our approach.

A two-way communication scheme for vehicles charging control in the smart grid

The smart grid is a new concept of electricity supply operation and management that will enable consumers and utilities to better control the electricity usage. This is possible because of the two way electricity and information communication between all nodes in the grid. For Electric Vehicles (EVs) travelling on the road, and because of the necessary battery charging times, there is a need for wireless communication between the EVs and the Electric Vehicle Supply Equipment (EVSEs) (charging stations) to discover the availability and make pre-reservations of charging time slots. In this paper, we introduce a new communication protocol between EVs and EVSEs that allows a reliable reservation process. The scheme, called Reliable Broadcast for EV Charging Assignment (REBECA) processes information about electricity usage in EVSEs and allows to reserve charging time slots for vehicles. REBECA also takes into account balancing energy usage between EVSEs while minimizing the latency time of EVs. Simulations results show the effectiveness of REBECA scheme.

About Deterministic and non-Deterministic Vehicular Communications over DSRC/802.11p

In this work, we introduce a priority-aware deterministic access protocol called Vehicular Deterministic Access VDA. VDA is based on 802.11p/DSRC and allows vehicles to access the shared medium in collision-free periods. Particularly, VDA supports two types of safety services emergency and routine safety messages with different priorities and strict requirements on delay. To avoid long delays and high packet collisions, VDA allows vehicles to access the wireless medium at selected times with a lower contention than would otherwise be possible within a two-hop neighborhood by the classical 802.11p Enhanced Distributed Channel Access or Distributed Coordination Function schemes. A non-VDA-enabled vehicle, that is, a vehicle not configured with the optional VDA capability over 802.11p, may start transmitting on the shared channel just before or during the VDA opportunities reserved for vehicles with VDA capabilities. To avoid the aforementioned issues and prevent interfering transmissions from VDA-enabled vehicles and non-VDA-enabled vehicles, we also proposed a novel scheme called extended VDA. We analyzed the impact of several design tradeoffs between the contention free period/contention period dwell time ratios on the performance of safety applications with different priorities for VDA and extended VDA. Simulations show that the proposed schemes clearly outperform the backoff-based schemes currently used by 802.11p in high communication density conditions while bounding the transmission delay of safety messages and increasing the packet reception rate. Copyright

Congestion-Aware Clique-Based Handoff in Wireless Mesh Networks

Wireless mesh networks (WMNs) have attracted increasing attention from the research community as a high-performance and low-cost solution to last-mile broadband Internet access. However, it remains an open challenge to provide mesh clients with efficient handoff among different mesh routers. In this paper, we address channel switching efficiency and load balancing capability during the handoff process. More specifically, (1) we introduce the concept of clique into WMNs to handle channel conflicts among neighboring mesh routers and thus achieve scalability; and (2) we propose a dynamic load balancing strategy for the handoff process, which integrates the mechanisms of mesh router selection and traffic admission control. Simulation results show that our proposed approach achieves significant gain in the handoff delay. Moreover, it provides good performance in terms of load balancing, loss rate and overall throughput.

MUDDS: Multi-metric Unicast Data Dissemination Scheme for 802.11p VANETs

Vehicular ad hoc networks (VANETs) leverage communication equipment and infrastructures to improve road safety. These networks, by the rapid change of their topology, can experience mainly two major problems; (1) the broadcasting storm and (2) the network disconnection due respectively to high vehicles density and their velocity. In this paper, we propose a new unicast data dissemination scheme based on distances estimation using Received Signal Strength (RSS) measurements and congestion detection by mean of a newly designed metric; called Multi-metric Unicast Data Dissemination Scheme (MUDDS). MUDDS adapts the transmission range so that congestion can be avoided. It performs the best available link choice to guarantee both reliable transmission and minimum delivery delay. MUDDS focuses on the broadcasting storm and the network disconnection problems simultaneously. Simulation results confirm the effectiveness of the proposed on-demand adaptation and relaying scheme and its impact on network performance under various traffic constraints.

An Enhanced Reservation Based Medium Access Control for Voice over Wireless Mesh Networks

Voice over IEEE 802.11 becomes much more cost effective when deployed over IEEE 802.11-based Wireless Mesh Network (WMN) due to the license-free backhaul wireless links. However, medium access control (MAC) based on IEEE 802.11 traditional random backoff protocols that are suitable for throughput-sensitive data services cannot satisfy the performance of voice services. Therefore, in this paper we propose an improved MAC based on medium reservations, called EMDA. EMDA improves significantly the optional Mesh Deterministic Access (MDA) MAC, to provide a much higher voice call capacity thanks to voice packet aggregation feasibility and much less MDA signaling overhead. EMDA is based on a per-node reservation of a block of contiguous transmission opportunities that are properly dimensioned. Moreover, we further improve the near-deterministic access of EMDA by using short jamming periods just before these reservations. Extensive simulation results show that our proposed MAC enlarges the voice capacity and uniformly distribute it over the WMN. It also provide a better performance in guaranteeing hard delay constraints, lower jitter and lower packet losses compared to other MAC.