Riadh Dhaou | ENSEEIHT Toulouse (original) (raw)

Papers by Riadh Dhaou

Cross layer techniques applied to various protocols stacks provide fair information sharing betwe... more Cross layer techniques applied to various protocols stacks provide fair information sharing between OSI model layers. The performance gains have been demonstrated for many studied systems within protocols interactions. The example is illustrative of the reliable transport protocols that use retransmissions to achieve that reliability function. The performance gains of the persistent timeout policy for the management of the retransmission timeout have been produce in some recent works when applying that persistent timeout policy only to reliable transport protocol. The goal was to give an appropriate behavior in response to a bad state of the wireless channel that occurs and temporally blocks the transmission of data. The channel state is given by the 802.11 link layer through cross-layer mechanism. In this paper, the persistent policy is extended to the network layer and is applied to a stack that uses a reactive routing protocol, namely the Destination Sequenced Distance-Vector (DSDV) protocol that also generates additional periodic traffic regardless to the channel state. We are measuring the influence in terms of performance gains of the extended persistent policy because of the additional periodic signalization messages deriving from the used routing protocol. After the introduction in section I; Section II of this paper presents an overview of the Stream Control Transmission Protocol (SCTP). Section III describes the behavior of the DSDV protocol. Section IV presents the extended persistent timeout policy principle and Section V presents the simulation results used to compare the using of the traditional and the extended persistent timeout policies applied to the same protocol stack using SCTP and DSDV.

In order to improve network performance, adaptive protocol would adapt to different aspects of th... more In order to improve network performance, adaptive protocol would adapt to different aspects of the network dynamic exhibited by the wireless systems and more particularly by the ad hoc networks. In this paper we consider the adaptation to the ad hoc network dynamic through two parameters: mobility and density. We study the impact part of the density metric and of the mobility metric. Considering the Optimized Link State Routing protocol (OLSR), our work focus on the Multipoint Relays (MPR) selection. A new approach to select a MPR by using a simple modification and no additional packet header is proposed. It introduces the idea of Link Duration criterion as mobility metric for MPR selection. From simulation results it appears that the protocol performance can be enhanced by mobility adaptation after the density one. The proposed scheme outperforms the standard protocol for large number of nodes.

Due to the unreliability characteristics of wireless communications, and nodes mobility, mobile a... more Due to the unreliability characteristics of wireless communications, and nodes mobility, mobile ad hoc networks demand robust protocol design. Hence, routing protocol choosing the most reliable route between two terminals have been proposed in order to minimize the path failure occurrence. The interest of this approach has been shown, in research literature, mainly by simulation in terms of delay or packet delivery ratio. Meanwhile, there is a problem to put in practice the route reliability paradigm. The route reliability depends on links reliability. The motivation of this paper is to determine a measure of the link reliability. In this paper, we study the link reliability formulation in order to propose a realistic wireless link parameters modeling. The modeling takes into account the mobility, the transmission quality, and the communication load. Reliability can be computed without extra signaling by each node.

Computer Networks, 2011

For extremely dynamic networks, such as ad-hoc, the topology change awareness has a crucial impac... more For extremely dynamic networks, such as ad-hoc, the topology change awareness has a crucial impact on the routing performance and consequently many routing protocols adapt their processes to the state of the network, from some network awareness. While several works have already been done on routing adaptations, this paper is more focused on the network awareness topic and the choice of the best metrics for a given adaptation. More precisely, the paper considers the way to represent by means of metrics the node mobility, the link degradation or the graph topology. The notion of metrics is illustrated through two adaptations of two well known ad hoc routing protocols (DSR, OLSR). We evaluate the effect of different metric choices by considering several adaptation strategies to the topology change which are based on the awareness of both the node movement and the number of nodes. We analyze the adaptation strategies and evaluate the performance of the adaptation depending on the chosen metrics. It is shown that the performance of adaptation is strongly correlated to the metrics that are themselves correlated to the network size. A metric combination based on link duration and number of nodes is found to be a good way to represent the topology change.

Journal of Networks, 2008

Cross-layer mechanism, for which a protocol locating at a given layer uses information issued fro... more Cross-layer mechanism, for which a protocol locating at a given layer uses information issued from other layers, may enhance the mobile networks performance. Some of those mechanisms are based on mobility metrics. For example, the establishment of a route by choosing less mobile nodes could improve the routing protocol. In this paper, we study the ability of mobility metrics to reflect the mobility influence over the protocol performances. The proposed approach evaluates the ability of a metric from its capacity to indicate or predict the routing protocol performance. Three routing protocols are considered: AODV, DSR and OLSR. The studied mobility metrics are Frequency of Link State Changes (LC), Link Connectivity Duration (LD) and Link Stability Metric (LS). The metrics are evaluated by simulation, firstly in a general case then in a scenario case.

Mobile networks performance may be enhanced by cross-layer mechanisms. Some of those mechanisms a... more Mobile networks performance may be enhanced by cross-layer mechanisms. Some of those mechanisms are based on mobility metrics. For example, the establishment of a route by choosing less mobile node could improve the routing protocol. In this paper, we study the ability of mobility metrics to reflect the mobility. The proposed approach evaluates the ability of a metric from its influence over routing protocols. Three routing protocols are considered: AODV, DSR and OLSR. The studied mobility metrics are frequency of link state changes (LC), link connectivity duration (LD) and link stability metric (LS). The metrics are evaluated by simulation, firstly in a general case then in a scenario case.

A new way to improve the performance of ad hoc networks consists in using cross layer mechanisms.... more A new way to improve the performance of ad hoc networks consists in using cross layer mechanisms. Currently, several protocols have demonstrated some reachable performance gain. Global integration on each level of the protocol stack has to be ensured. We present some efficient methods that may either produce or update cross-layer models. Those models, developed on different levels, allow an efficient organisation of the wireless systems and could take several forms. A cross-layer conceptual model is composed of: cross-layer interaction models and interactions description arrays. In this paper, we propose a method which has been applied to a chosen protocol stack.

Mobility issue and service continuity represent important challenges for next generation networks... more Mobility issue and service continuity represent important challenges for next generation networks. The integration of a satellite segment within a terrestrial network (especially WiMAX) has several advantages in a 4G context. In this paper, we focus on channel reservation mechanisms to ensure quality of service. Primary results show, by means of simulation, the gains and limitations of each mechanism. It is shown that the best results are obtained when the mechanisms are performed by the base stations when the density of users is low. Otherwise, cooperative solutions for which reservations are done by neighboring nodes may improve the performance of the system.

In this paper, we highlight the extent of the effects of topological specificities on the deploye... more In this paper, we highlight the extent of the effects of topological specificities on the deployed solutions, which can be useful to refine already proposed models as well as to carry out protocol tuning or adjustments. We present, an intensive experimental study on wireless Link Quality Indicator (LQI). Using Moteiv’s Tmote Sky sensors, we deployed multiHopLQI algorithm of TinyOS in various network configurations: homogeneous and heterogeneous; straight-line and grid topologies with various transmission power levels and distances. Initially, we study LQI time-varying and try to understand the relationship between transmission power level, distance and link quality and present how some random disturbances due to external (physical changes) or internal phenomena (node movement,power variation) may affect the dynamics of the network. Later, we address impacts and side effects of position and power transmission level of some important nodes in the network like the Base Station in such LQI based algorithms.

Abstract Long Term Evolution (LTE) prevails as the next 4th generation of mobile communications. ... more Abstract Long Term Evolution (LTE) prevails as the next 4th generation of mobile communications. Hybrid satellite and terrestrial LTE network takes advantages from the large satellite coverage for several emergency applications, such as providing civil ...

Abstract In this paper, we propose an adaptive time-based channel reservation mechanism (ATCR) su... more Abstract In this paper, we propose an adaptive time-based channel reservation mechanism (ATCR) suitable for handover and call admission procedure control in future multiservices mobile satellite systems. These systems are characterized by a high rate of handover. ...

The Cross layer concept is a new way to see the quality of service in the network. It consists in... more The Cross layer concept is a new way to see the quality of service in the network. It consists in adapting the current mechanisms at one level to the underlying levels and the definition of information to share between, not necessarily adjacent, levels and the global optimisation instead of multiple optimisations. Performance optimisation of the whole system is a crucial step in the process of design and validation of new systems. Models of large, complex and dynamic systems can often be reduced to smaller sub-models, for easier analysis, by processes known as decomposition or aggregation methods. Those techniques have to be implemented in a dynamic simulation tool. It has to be dynamic because simulations are driven by dynamic data and entail the ability to incorporate additional data (either archived or collected online) and reversely the simulator will be able to dynamically steer the measurement process.

This paper compares several approaches for dynamic allocation in geo-stationary networks based on... more This paper compares several approaches for dynamic allocation in geo-stationary networks based on DVB-RCS system. Each Satellite Terminal (ST) regularly sends requests to the Network Control Center (NCC) which in turn allocates resource to the users. Unfortunately, this delayed request-assignment makes the dynamic bandwidth allocation very difficult. Simple mechanisms such as a fixed allocation or requests based on the current size of the terminals’ queue are compared to predictive methods based on control theory techniques which have been previously proposed. A lower bound is also derived by considering that the actual size of the buffer can be instantaneously known. It is shown that if the traffic is not really bursty, a fixed allocation which implies lighter signalling mechanisms leads to good results. In bursty traffic conditions, simple mechanisms for which the requests correspond to the actual size of the buffer may lead to the best performance results.

This paper introduces cross-layer implementation with a multi-rate aware routing scheme and shows... more This paper introduces cross-layer implementation with a multi-rate aware routing scheme and shows that SNR is an important information to use in a routing protocol. The existing routing protocol attempts to minimize the number of hops between source-destination pairs. We use a new metric definition to route the packets and to select the best available link along the path in a multi-rate protocol senario. The new metric is created with information coming from inter-layer interaction between the routing layer and the MAC layer. We use SNR as an information about link quality. We show through simulation that for communications using muti-rate protocol in ad hoc networks, throughput is highly affected as soon as the route goes through low-rate link.

Next generation networks will be characterized by variable and high data rates, QoS, and seamless... more Next generation networks will be characterized by variable and high data rates, QoS, and seamless mobility, within a network and between heterogeneous networks with different technologies and service providers. In this paper, we consider a model of mobility for WiMAX network users introducing horizontal handover mechanism with channel reservation. We take into account several approaches in order to carry out the reservation. We evaluate the performance of the proposed model. The results show, by means of simulation, that channel reservation mechanism improves horizontal handover without reducing the performance of the system.

The paper presents the problem of minimizing energy consumption and lifetime maximization in a ma... more The paper presents the problem of minimizing energy consumption and lifetime maximization in a many-to-one sensor network. In such network pattern, all sensor nodes generate and send data to a single and fixed sink (base station), via multihop transmissions. When all the sensor data have to be forwarded to a single base station via multi-hop routing, the traffic pattern is highly non-uniform, putting a high burden on the sensor nodes close to the base station. Some strategies that balance the energy consumption of the nodes and ensure maximum network lifetime by balancing the load are proposed and analyzed. The key element of the research is the use of multiple transmission power levels. We studied an optimal solution for calculating the hop-by-hop traffic proportions for the particular case of nodes having just two transmission power levels, and compared the results given by the heuristics with those from the optimal analytical case. Another goal is to propose and implement a systematic approach for the construction of the sensor network based on real sensor nodes. The neighbor discovery phase, the way in which the base station finds out the network topology and than impose the strategy and decide whether the nodes to act locally or respect the instruction from the sink are part of the protocol that is described in the paper.

ABSTRACT The lifetime of Wireless Sensor Networks (WSN) is crucial. The goal of all WSN applicati... more ABSTRACT The lifetime of Wireless Sensor Networks (WSN) is crucial. The goal of all WSN application scenarios is to have sensor nodes deployed, unattended, for months or years. In this work, we investigate the problem of energy consumption and lifetime maximizing in a many-to-one sensor network. In such network pattern, all sensor nodes generate and send data to a single sink via multihop transmissions. In our previous experimental studies, we noticed that, since all the sensor data has to be forwarded to a base station via multihop routing, the traffic pattern is highly nonuniform, putting a high burden on the sensor nodes close to the base station. In this paper, we analyze and propose some strategies that balance the energy consumption of these nodes and ensure maximum network lifetime by balancing the load as equally as possible.

Wireless sensor networks (WSN) have received much attention during the last few years especially ... more Wireless sensor networks (WSN) have received much attention during the last few years especially with regard to energy consumption and scalability. In this paper, we will focus on mechanisms which may be implemented for small WSNs. So, in the present work, we design energy-aware selforganization algorithms for WSNs in such a context. These algorithms can be used to design effective and adaptive protocols. The first protocol concerns the initialization or the setting up of the network topology under a chain form. The second one (steady-state protocol) implements the communication part or the information exchange between the different nodes of the chain. Our algorithms were dimensioned and validated by an analytical model. We also perform a detailed study of these algorithms by using TOSSIM, a simulation environment for TinyOS, the operating system for the Berkeley sensor nodes. Finally, we achieve an experimental test using Tmote Sky nodes, a popular commercial hardware platform for wireless sensor systems. The results emphasize the interest of the proposed algorithms.

Computer Networks, 2011

Journal of Networks, 2008