Summary As sensor nodes are power constrained, saving energy and prolonging network lifetime have been given the greatest priority in the design of routing protocols in wireless sensor networks (WSNs). In this regard, duty‐cycling is broadly utilized as an underlying MAC (Medium Access Control)‐based protocol for routing solutions. In this regard, a cross‐layer approach, integrating MAC and routing protocols, is required to achieve a trade‐off between energy efficiency and communication reliability, through adapting nodes duty‐cycle to routing decisions. Besides, with the proliferation of WSNs applications in various domains, achieving energy efficiency should not be performed while ignoring the diverse quality of service (QoS) demands of the considered applications to ensure their well functioning. In this context, we propose a context‐aware routing framework under duty‐cycled networks, a generic framework that allows to support heterogeneous applications and traffic patterns. An evaluation of the framework is also proposed in this paper. Results prove the effectiveness of context‐awareness and the cross‐layer interaction between the different modules of the framework to guarantee desired QoS while reducing energy consumption.

Summary The specific characteristics of vehicular ad hoc networks, such as high speed of nodes and frequent topology changes, impose challenges for the routing process. In addition, the advent of the Internet of Vehicles (IoV) concept along with the autonomous and connected cars contribute to the proliferation of new innovative applications with different quality of service requirements, rising new challenging issues for data transfer. In this article, we review the different taxonomies of vehicular routing protocols, while giving an insight into the design of geographical protocols. Then, we outline several optimization techniques and paradigms used to enhance the routing process. Moreover, in order to promote the deployment of robust IoV routing protocols at large scale, we provide some directions for future research work.

Vehicular cloud computing is an emerging research area which integrates the conventional cloud with the vehicular ad hoc networks. This paradigm allows vehicles to access cloud services and/or share their underutilized on-board resources. Security is an essential concern for users during cloud services access and on-board resources sharing. Thus, we are interested in this work to propose a secure vehicular cloud framework that ensures authentication and privacy requirements. The performance of this framework was evaluated and compared with related works. The results show the effectiveness of this framework in terms of authentication overhead and average authentication delay.

Vehicular Cloud Computing is an emerging paradigm that integrates cloud computing technology within vehicular networks in a way to use and share available underutilized resources. The aim is to virtualize the vehicular network resources in a way to make them available services for applications within the networks. As such, the architectural design stands out as a main concern before been able to be put into practice. We address in this paper three related issues to vehicular cloud architectures namely: taxonomy, security and challenges. We first review the relevant existing taxonomies and then we propose a new one. Secondly, we address the security aspects that should be taken into consideration. Thirdly, we identify the different challenges that need to be solved. Finally, we summarize and provide a comparative analysis of the reviewed architectures.

This work highlights the key factors considered to evaluate the performance of a Localization System (LS) for W SNs. Indeed, the majority of the existing works concentrated essentially on the accuracy of the estimated location by the LS and ignored its performance in terms of localization cost, scalability and coverage. To address the accuracy/cost trade-off of a LS for WSNs, this work attempted to redefine and reformulate the Sensor Network Localization Problem (SNLP) as a Multi-Objective Optimization Sensor Network Localization Problem (MOO-SNLP). The latter requires the consideration of multiple objectives, like the position accuracy enhancement, with a reduced energy consumption, communication overhead and deployment cost of a localization approach. Moreover, we highlight the performances of the two most commonly-used localization approaches, Recursive Position Estimation (RPE) and Centroid Localization Algorithm (CLA), using different metrics under simulations. In fact, the obtained results show that the trade-off between location accuracy and implementation cost is promising in the area of multi-objective optimization related to SNLP.

In recent years, clustering has emerged as a promising approach to facilitate data routing and data aggregation in Wireless Sensor Network (WSN). Although clustering based routing approaches are appropriate for small-scale networks, they do not fit large scale WSNs as it is the case in LEACH [1]. Indeed, clustering suffers from the adverse effects of isolated nodes in the network and some coverage problems. To deal with these issues, we present LEATCH-L, a Low Energy Adaptive Tier Clustering Hierarchy for Large scale WSNs. The proposed approach makes the major functions of LEACH applicable to large-scale WSNs whose dimension is much larger than the largest transmission radius of the sensor nodes. The latter imposes a dynamic decomposable structure on the network topology which results in a set of smaller subnetworks. Such decompositions are implemented through a smart m-level hierarchical clustering process. Moreover, the proposed approach involves a two level data aggregation. Evaluation results show that the introduced approach is scalable with significantly much better performance than the state-of-the art approaches.

Internet of Vehicles (IoV) constitutes an important part of the Smart Cities concept, relying on different technologies and including heterogeneous cars types, which raises challenges to ensure and preserve road safety. Throughout this paper, we tackled the data collection and transmission problems related to the safety in the terrestrial domain by identifying the car-types and exposing the different communication data levels and means used in the quest of safety realization.

Wireless Body Area Networks are nowadays attracting both academic and industrial worlds. Combining collected data related to patient context with original health measurement can enhance the general health state monitoring and help to better understand the patient disease evolution. Daily activity is one of the important features that may influence the patient health state. Thus, recognizing the user activity can be a useful way for improving quality of health services. Relying on supervised learning, we study the feasibility of extracting and classifying the human activities from channel gain measures, which is an important feature that characterizes the WBAN channel links.

The Information-Centric Networking (ICN) paradigm is shaping the foreseen future Internet architecture by focusing on the data itself rather than its hosting location. It is a shift from a host-centric communication model to a content-centric model supporting among others unique and location-independent content names, in-network caching and name-based routing. By leveraging the easy data access, and reducing both the retrieval delay and the load on the data producer, the ICN can be a viable framework to support the Internet of Things (IoT), interconnecting billions of heterogeneous constrained objects. Among several ICN architectures, the Named Data Networking (NDN) is considered as a suitable ICN architecture for IoT systems. However, its default caching approach lacks a data freshness mechanism, while IoT data are transient and frequently updated by the producer which imposes stringent requirements in terms of information freshness. Furthermore, IoT devices are usually resource-constrained with harsh limitations on energy, memory and processing power. We propose in this paper a caching strategy and a novel cache freshness mechanism to monitor the validity of cached contents in an IoT environment while minimizing the caching process cost. We compared our solution to several relevant schemes using the ccnSim simulator. Our solution exhibits the best system performances in terms of hop reduction ratio, server hit reduction ratio and response latency, yet it provides the lowest cache cost and significantly improves the content validity.

This article describes how the named data networking (NDN) has recently received a lot of attention as a potential information-centric networking (ICN) architecture for the future Internet. The NDN paradigm has a great potential to efficiently address and solve the current seminal IP-based IoT architecture issues and requirements. NDN can be used with different sets of caching algorithms and caching replacement policies. The authors investigate the most suitable combination of these two features to be implemented in an IoT environment. For this purpose, the authors first reviewed the current research and development progress in ICN, then they conduct a qualitative comparative study of the relevant ICN proposals and discuss the suitability of the NDN as a promising architecture for IoT. Finally, they evaluate the performance of NDN in an IoT environment with different caching algorithms and replacement policies. The obtained results show that the consumer-cache caching algorithm used with the Random Replacement (RR) policy significantly improve NDN content validity in an IoT environment.

Oblivious Random-Access Memory (ORAM) is becoming a fundamental component for modern outsourced storages as a cryptographic primitive to prevent information leakage from a user access pattern. The major obstacle to its proliferation has been its significant bandwidth overhead. Recently, several works proposed acceptable low-overhead constructions, but unfortunately they are only evaluated using algorithmic complexities which hide valuable constants that severely impact their practicality. Four of the most promising constructions are Path ORAM, Ring ORAM, XOR Ring ORAM, and Onion ORAM. However, they have never been thoroughly compared against each other and tested on the same experimental platform. To address this issue, we provide a thorough study and assessment of these recent ORAM constructions and implement them under the same testbed. We perform extensive experiments to provide insights into their performance characteristics, simplicity, and practicality in terms of processing time, server storage, client storage, and communication cost. Our extensive experiments show that despite the claimed algorithmic efficiency of Ring and Onion ORAMs and their judicious limited bandwidth requirements, Path ORAM stands out to be the simplest and most efficient ORAM construction.

Conflict detection is an important research issue in Unmanned Aerial Vehicles to ensure safety and collision free flights. In this paper, we first propose a comprehensive analytical framework for a three dimensional conflict detection. Then, we propose SLIDE a new Straight LIne conflict DEtection and alerting algorithm for a set of UAVs to safely share a common airspace. SLIDE is fully distributed and requires a limited state information exchange between UAVs. The assumptions of precise state information and packet-loss free communications are relaxed so as to guarantee the applicability and efficiency of the algorithm in real world situations. A thorough discussion is also presented to deal with appropriate tuning of the different parameters of the collision detection framework. Extensive simulations based on OMNeT++ are used to validate SLIDE and evaluate its performance. Simulation results indicate that SLIDE guarantees a reduced number of false and missed alarms even in high density traffic scenarios and communication perturbed environments, yet it leaves adequate time to accomplish the required maneuver actions.

Although recursive localization approaches stand well in small-scale networks, they are unsuitable for largescale WSNs. Indeed, they suffer from the adverse effects of error propagation and accumulation. They also require an important communication overhead related to the localization data broadcasted by new reference nodes. To deal with these issues, we developed a new reliable reference selection strategy that ensures a better distribution of these nodes. Our approach couples the novel selection strategy with a refinement phase that enhances the position accuracy. Simulations show that our approach consistently reduces the position error, while it requires less communication overhead. Moreover, it conserves the energy, which helps enhance the WSN lifetime.

Information-Centric Networking (ICN) is an emerging network paradigm based on name-identified data objects and in-network caching. Therefore, ICN contents are distributed in a scalable and cost-efficient manner. With the rapid growth of IoT traffic, ICN is intended to be a suitable architecture to support IoT networks. In fact, ICN provides unique persistent naming, in-network caching and multicast communications which reduce the data producer load and the response latency. Using ICN in an IoT environment requires a study of caching policies in terms of cache placement strategies and cache replacement policies. To this end, we address, in this paper, caching challenges with the aim to identify which caching policies are suitable for IoT networks. Simulation findings show that the combination of the consumer-cache caching strategy and the RR cache replacement policy is the most convenient in IoT environments in terms of hop reduction ratio, server hit reduction and response latency.

Internet of Mobile Things (IoMT) is a new paradigm of the Internet of Things (IoT) where devices such as sensors, robots, unmanned aerial vehicles (UAV) and cars, are inherently mobile. While mobility enables innovative applications and allows new services, it remains a challenging issue as it causes disconnection of nodes and intermittent connectivity, which negatively impact the network performance; namely data loss, large handover delay and application functionality failures. In this paper, we propose a new energy efficient and mobility aware routing protocol named EC-MRPL based on the well-known Routing Protocol for Low power and Lossy Networks (RPL standard). Unlike RPL which is designed for low resources networks with basically static devices, the proposed protocol enables to better conserve the energy and sustain the connectivity of mobile nodes. EC-MRPL integrates an enhanced mobility detection method and a novel point of attachment prediction and replacement strategy aware of the resources constraints. As such, EC-MRPL overcomes and mitigates problems caused by mobility. Obtained simulation results using Cooja/Contiki show that EC-MRPL outperforms both the RPL and the MRPL protocols in terms of handover delay, data loss rate, signaling cost and energy consumption.

As the energy efficiency remains a key issue in wireless sensor networks, duty-cycled mechanisms acquired much interest due to their ability to reduce energy consumption by allowing sensor nodes to switch to the sleeping state whenever possible. The challenging task is to authorize a sensor node to adopt a duty-cycle mode without inflicting any negative impact on the performance of the network. A context-aware paradigm allows sensors to adapt their functional behavior according to the context in order to enhance network performances. In this context, the authors propose an enhanced version the Efficient Context-Aware Multi-hop Broadcasting (E-ECAB) protocol, which combines the advantages of context awareness by considering a multi criteria and duty-cycle technique in order to optimize resources usage and satisfy the application requirements. Simulation results show that E-ECAB achieves a significant improvement in term of throughput and end-to-end delay without sacrificing energy efficiency.

The wide proliferation of wireless sensor networks in various domains has lead to the emergence of numerous applications with different requirements to satisfy for the well functioning. It is imperative to develop different approaches and communication protocols to meet these diverse and specific requirements while considering the most critical constraint, network lifetime. Adopting duty cycling is an efficient way to conserve energy, by allowing nodes to turn off their radio whenever possible. With these intermittent sleeping periods, it is hard to meet short delay delivery for real time traffic in duty cycled networks, since involved nodes in forwarding are not always awake. For delay intolerant applications, providing an always-on path without scarifying energy can be an effective solution. In this context, we propose a node-disjoint multipath routing algorithm, operating under duty cycled environment, to construct n complementary paths from the source towards the sink. To support urgent data transfer from sources of critical traffic, our protocol aims to offer always at least one available path while others are down. Simulation results show good performances in term of energy consumption and the number of exchanged packets control with a relative small increase in paths establishment time.

Buffering mechanisms play a vital role in leveraging the capacity and efficiency of live streaming as well as P2P streaming system. An appropriate buffering mechanism allows the peer to undergo a smooth playback by compensating the delay introduced by the network as well as storing pieces to be played in the near future. A circular buffer is used most of the time in a live P2P streaming system as the media duration is not known in advance. When the speed of the downloading process exceeds the speed of the playback process, some not-yet-played pieces my be erased which affects in turn the playback quality. In this paper we investigate this problem through extensive simulations done without loss of generality in the context of our recently proposed P2P protocol named HLPSP and we propose a pieces requesting control mechanism to avoid such a problem. The simulations results show that the proposed mechanism eliminates the erasing phenomena which decreases the rate of the missed pieces during the playback process.

In Vehicular Ad-hoc Networks (VANETs), any vehicle uses a location service to get an up-to-date data of all vehicles' positions in its vicinity. Many location services rely on infrastructures to perform location update and location query tasks. However, the infrastructure penetration rate may differ from one region to another. We propose in this paper a new location service called Vehicle-Aided Location Service in urban environment (VALS) which resolves the problem of the shortage of infrastructure in some city districts. VALS replaces the missing Road-Side Units (RSU) with vehicles offering RSUs functionalities. It is based on a hierarchical and cluster-based design. Simulation results show that VALS achieves a high success ratio (86%), get most vehicles' data (82%) and a good position information level accuracy (less than 20 m) with a low RSU penetration rate (40%).

Context-awareness has gained an increasing popularity in ubiquitous computing environments as it allows automatic adaptation of protocols behavior according to context changes. Nowadays, wireless sensor networks (WSNs), deployed as a main appliance to gather contextual information, can benefit from their own context data. In such scarce resource networks, the concept of context-awareness can be exploited either to optimize resource usage or to enhance the functional behavior of operating protocols. In this paper, we investigate the benefits brought by the concept of context-awareness when exploited in duty-cycled networks, since WSNs rely mainly on power saving mode in order to prolong the lifetime of sensor nodes. We focus mainly on the broadcast operation required for data collection and routing task. To quantify these improvements, we propose a comparative study relying on our ECAB protocol, using context-awareness jointly with a duty cycle mechanism to assure an efficient multi-hop broadcasting. To this end, we compare ECAB against protocols operating without context-awareness. Results show the effectiveness of this concept to improve network performances related to energy consumption, latency and packet delivery.

In Wireless Ad Hoc Networks, synchronization is a prerequisite to many basic operations such as frequency hopping, power saving, free contention channel access, clustering and security. Clock synchronization requires the availability of a common time reference for all mobile nodes. However, a synchronization algorithm cannot converge quickly to a stable point without considering the effects of collisions and channel interference inherent to wireless environments. In this paper, we propose a Fast Synchronization Protocol with Collision Handling for multi hop wireless ad hoc networks. Performance evaluation results show the ability of our algorithm to improve the convergence time and to assure the network wide synchronization accuracy even in highly dynamic scenarios.

This paper deals with conflict detection for Unmanned Aerial Vehicles (UAVs). We provide an exhaustive mathematical framework for 3D conflict detection and propose a novel distributed conflict detection algorithm. The suggested algorithm requires minimal communication. Indeed, only the state information (i.e., position and velocity vectors) is periodically exchanged between the UAVs. We carry out simulations, using the OMNET++ simulator, to evaluate its performance. Simulation results indicate that the proposed algorithm performs well in terms of false alarms, missed alarms and scalability to increased number of UAVs.

Abstract Ad hoc wireless communications rely on beaconing to manage and maintain several network operations and to share relevant network parameters among network nodes. Beacon frames are sent at the start of each beacon interval. The frequency of beaconing depends on whether beacon intervals are fixed size or may be adapted and regulated according to the perceived network and workload conditions. On the other hand, current mobile nodes usually embed several heterogeneous wireless interfaces that urge the design of an adaptive beaconing strategy. In this paper, we propose an autonomous and adaptive beaconing strategy for multi‐interfaced mobile wireless nodes that is capable of regulating the beacon interval size dynamically according to the perceived network conditions. The proposed strategy is based on a joint dynamic estimation of both the announcement traffic indication message (ATIM) window and the beyond‐ATIM window sizes for each beacon interval. Extensive simulations were conducted using OMNeT++ to ascertain the improvements achieved by autonomously regulating the entire beacon interval to take into account the network and workload conditions. Obtained results showed that the two proposed approaches improve significantly the efficiency of the network in terms of throughput, end‐to‐end delay, and power consumption. The proposed fixed beacon interval (fixed‐BI) approach stands as an enhanced version of the power‐saving multi‐channel MAC protocol (PSM‐MMAC). The proposed variable beacon interval (variable‐BI) approach, which regulates dynamically both of the ATIM and the beyond‐ATIM windows, outperforms both the fixed‐BI and the PSM‐MMAC. In particular, under nominal traffic loads, the end‐to‐end delay of the variable‐BI is much lower than those provided by the fixed‐BI and PSM‐MMAC. Copyright © 2015 John Wiley & Sons, Ltd.

In this paper, we propose an Extended-LEACH protocol that integrates an efficient multi-hop routing scheme in distributed clustering algorithms. In addition to energy saving, Extended-LEACH solves the issue of isolated cluster head nodes. The latter appear especially when distributed clustering protocols are deployed in wide wireless sensor networks. In contrast to some earlier work, Extended-LEACH allows both cluster head and non-cluster head nodes to appear in multi-hop routing paths. Such a choice enhances the network connectivity and improves the delivery of aggregated data packets. Extended experimentations and simulations are used to position and ascertain the performance of our proposed Extended-LEACH protocol against relevant earlier work. Results clearly show that Extended-LEACH provides a higher packet delivery ratio compared to both LEACH and MH-LEACH, yet it incurs much less signaling overhead than MH-LEACH.

Nowadays, the Peer-to-Peer (P2P) Video-on-Demand (VOD) systems knows a huge success for several reasons: a) each peer is both server and client leading to scalable system, b) it is not necessary to build and maintain infrastructures. BitTorrent is the most popular P2P file sharing protocols due to its effectiveness in the delivery of content. Thus, many VoD protocols have been proposed based on it. They investigate new ways for pieces and neighbor peers selections to assure the tight displaying time deadlines of video frames. In this paper, we present an up-to-date literature review of the main P2P VoD works based on the BitTorrent protocol. Furthermore, we propose a taxonomy of these works considering the pieces and the peers selection algorithms criterions.

Duty-cycling scheme consists in switching between active and sleeping modes. While this technique is widely exploited in WSNs to reduce power consumption, It raises several challenges especially for broadcast communications. In fact, as many neighboring nodes are involved in the communication, keeping them all active during a specific period of time requires a preliminary synchronization process which is a complex task and causes extra overhead. In this context, we propose an Efficient Context-Aware multi-hop Broadcasting (ECAB) over asynchronous duty cycled networks. ECAB exploits both the neighborhood knowledge and the traffic load conditions to regulate node behaviors and dynamically adjust duty-cycling schedules. Our objective is to reduce energy consumption without performances penalties. Simulation results show that ECAB outperforms RI-MAC and greatly improves energy consumption compared to broadcast under always-on networks with small degradation related to end-to-end delay and packet delivery.

Information-Centric Networking (ICN) is a new paradigm proposing a shift in the main Internet architecture from a host-centric communication model to a content-centric model. ICN architectures target to meet user demands for accessing the information regardless of its location. A major building block of ICNs concerns caching strategies. Concomitantly, Machine-to-Machine (M2M) technologies are considered the main pattern for the Internet of Things (IoT). Unifying M2M and ICN into a single framework raises the challenge of cache coherence. In this paper, we propose a novel cache coherence mechanism to check the validity of cache contents. We also propose a caching strategy suitable to M2M environment. Extensive experimentations are conducted to evaluate the performance of our proposals. They show that the combination of our two proposed schemes results in a notable improvement in content validity at the expenses of a certain degradation in both server hit and hop reduction ratios.

Multipath routing has been widely used in wireless sensor networks to improve mainly the network performance by providing the load balancing capabilities. However, high correlated paths can throttle data transfer and can cancel the benefits of using multiple routes for data forwarding towards the sink. In this context, we propose a Fast Multipath Routing Protocol (FMRP), a query based multipath routing protocol which provides a simple mechanism during the discovery phase to construct node-disjoint paths while minimizing the impact of collision and interference. Thus, selecting less correlated paths allows a fluent data transfer and an efficient resources use. The good performance of our protocol in terms of more energy saving and better network throughput is witnessed by extensive simulations under various traffic loads and adopting different scenarios.

The number of vehicles on roads keeps increasing continuously, making the management of traffic flow, especially in big cities more and more challenging. One of the key enablers for having smooth traffic flows and better mobility is to rely on real-time traffic monitoring systems. These systems allow road operators to implement intelligent traffic management strategies such as the dynamic adjustment of timing and phasing of traffic lights and the adaptive road congestion charging. Moreover, better informed travelers will plan smartly their journeys and hence potentially contribute in reducing traffic jams. Traditional real-time traffic monitoring usually get real-time data from GPS-equipped fleets and fixed sensors installed in specific locations. In this paper, a new real-time traffic monitoring based on emerging vehicular communication systems is proposed. The system enables traffic monitoring with higher reliability, accuracy, and granularity. The cluster-based V2X traffic data collection mechanism is able to gather more than 99% of the available data and reduce the overhead to one quarter when compared to other approaches.

Sensing coverage in wireless sensor networks is one of the most fundamental issues, which have been extensively addressed in the literature. It is viewed as one of the critical performance measures in large-scale sensor networks. In this context, researchers have designed several coverage protocols. Throughout the variety of research works in this topic, most interests focused purely on the coverage problem under the restrictive assumption that each deployed node is equipped with a GPS receiver that provides a sensor node with its accurate location. However, in some wireless sensor network applications GPS service may be inaccessible, unpractical and very expensive. Faced to this challenge, several GPS-less localization algorithms for wireless sensor networks have been proposed. Such localization algorithms enable sensor nodes to locate themselves with some degree of accuracy. In this paper, we address the issue of maintaining coverage from the perspective of a GPS-less localization. We particularly integrate two well-known coverage and GPS-less localization solutions, namely CCP and AT-Dist. This integration yields key insights for handling coverage and GPS-less localization in a unified framework in contrast to several existing approaches that address the two issues in isolation. To the best of our knowledge, this will be the first work that integrates those two solutions. Extensive simulations show the effectiveness of this integrated framework to provide guaranteed coverage and localization.

Automated verification tools are required to detect coding errors that may lead to severe software vulnerabilities. However, the usage of these tools is still not well integrated into software development life cycle. In this paper, we present our approach that brings the software compilation process and security verification to a meeting point where both can be applied simultaneously in a user-friendly manner. Our security verification engine is implemented as a new GCC pass that can be enabled via flag-fsecurity-check=checks.xml where the input XML file contains a set of user-defined security checks. The verification operates on the GIMPLE intermediate representation of source code that is language and platform independent. The conducted experiments demonstrate the scalability, efficiency and performance of our engine used to verify large scale software, especially the entire Linux kernel source code.

ABSTRACT In this paper, we propose a distributed and dynamic public key infrastructure for vehicular ad hoc networks. We aim to achieve the fundamental security requirements, particularly the authentication, the confidentiality, and a reliable vehicle‐to‐vehicle data exchange. To make the certification authority (CA) reachable by all vehicles, we distribute its role among a set of dynamically elected vehicles. The election of dynamic CAs is based on a clustering algorithm where the cluster heads will be CAs in their clusters. The cluster heads are elected following two criteria: security and mobility. Due to the important role of the CA in each cluster and to protect it from DOS attacks, we introduce a VANETs dynamic demilitarized zone for vehicular ad hoc networks. Its role is to handle the certification requests sent to the CA from unknown vehicles, and hence, it avoids compromising it. Additionally, we detail the certificates management in the proposed public key infrastructure, and we propose a mechanism to provide anonymous vehicle‐to‐vehicle communications using pseudonyms. To study the feasibility of our distributed architecture and particularly the clustering algorithm, we propose a probabilistic model considering the speed of vehicles and taking into account the safety distance between vehicles. We carried out a set of simulations to evaluate the performance of the proposed clustering algorithm in both urban and highway environments. Hence, we study the effects of the transmission range, the speed of vehicles, and the number of trusted vehicles in the network on the stability and the efficiency of the overall proposed architecture. We also study some delays characterizing the certificates management. Our simulation results show that the security of the proposed architecture closely depends on the number of trusted vehicles in the network, and the stability depends on the mobility of vehicles on the road and on the total number of trusted vehicles. Copyright © 2013 John Wiley & Sons, Ltd.

The HIP-Based M2M Overlay Network (HBMON) is a virtual, self-organized and secure M2M network built on the top of Internet, composed of scattered mobile devices. A fundamental requirements of this overlay network is to ensure session survivability upon end-host movement. The Host Identity Protocol (HIP) provides a regular mobility support in our M2M Overlay network. However, HIP is not able to handle the simultaneous mobility case, where both communicating end-points simultaneously acquires a new topologically correct IP address. We propose in this paper a novel solution to manage the simultaneous mobility (also known as double jump) of M2M devices within our overlay. For this purpose we enhance the HIP rendez-vous server in order to fully manage the double jump case. We analytically evaluate the signaling cost of our solution. Then, we implement our double jump solution within the OMNeT++ network simulator. Finally, we evaluate the application recovery time of an M2M device experiencing a double jump situation.

Wireless sensor networks (WSN) have received significant attention over the last few years as they afford a growing number of applications in various fields. At the same time, these networks provide numerous challenges due to their constraints, primarily related to energy scarcity. To overcome energy waste caused by collisions and contention based algorithm, the channel assignment mechanisms, like TDMA1, seem to be an effective way for scheduling node transmissions. To solve channel assignment problems, graph coloring theory has been exploited in many research works, primarily in order to assure collision-free communications. In this paper, we present a novel distributed coloring algorithm for WSNs taking into account the constraints of a real WSN environment. Our collision aware coloring algorithm assures a 2 hop nodes coloring, in a deterministic time execution, without requiring a neighborhood discovering phase. Performance evaluation results have shown the effectivness of our algorithm in terms of exchanged control packets per node as well as the chromatic number.

The localization problem in wireless sensor networks often raises the crucial question that to what extent higher location estimation accuracy can be achieved at the cost of additional energy consumption. To obtain a trade off between location accuracy and energy consumption in wireless sensor networks, it is necessary to have a global vision where both the localization scheme and its induced computational complexity are jointly addressed. However, throughout the variety of research works in this topic, much emphasis has been primarily placed on the localization scheme itself and even when the energy consumption issue is addressed, little insight is often provided to the computational complexity issue. Instead, our take in this work is to revisit SeRLoc, a well-known localization algorithm, by analyzing its algorithmic complexity and then proposing a novel method that reduces its computational complexity while preserving its location accuracy. Analytical results and extensive simulations show that the enhanced version of SeRLoc, called E-SeRLoc, achieves the same degree of location accuracy as the original version while paying less complexity cost, thereby reducing the energy consumption.

In recent years, the use of random walks (RW) for data forwarding in wireless sensor networks (WSN) has gained a lot of popularity. However, a negative effect is often caused by the fact that a completely uniform random choice of the next hop during the walk translates into a reduced progress towards the sink node, thereby yielding a long latency. Several strategies are proposed to attenuate this problem. Most of them are characterized by their dependence on state information stored in sensor nodes in order to bias the direction of the walk towards the target. Such information require additional capabilities and it is costly in terms of complexity and energy, which is inherently problematical in WSN. This leads to a tradeoff between mutually contradictory goals and raises the question as to what extent biasing RW can affect the performance of the data forwarding scheme. This question is our primary motivation in investigating the problem of biasing RW based data forwarding from a pure analytical perspective.

This paper introduces CrossWalk, a novel integrated cross-layer medium access control/routing protocol based on a receiver-oriented contention resolution mechanism for data dissemination in wireless sensor networks. Traditional approaches for data dissemination such as flooding or simple random walks suffer respectively from a large message forwarding overhead and an excessively long cover time. In this scope, CrossWalk, based on biased random walks, aims to achieve a convenient cover time at the cost of a reasonable overhead. In particular, we demonstrate by an analytical study that the proposed biasing strategy based on a decreasing truncated geometric distribution over a fixed contention window favors a data packet to progress-in a unicast fashion-towards nodes in less explored vicinity by making them more likely to win the contention for the medium access. We therefore show by extensive simulations that CrossWalk outperforms common random walks in terms of partial coverage and efficient network resources consumption by making less redundant message transmissions.

In this paper we propose a trust model based on a Markov chain in order to formalize the trust metric variation and its stability in the context of Vehicular Ad hoc Networks (VANETs). The proposed model takes into account not only the dynamic trust metric variation according to the vehicles behaviors, but also the constraints related to the monitoring process. In our model each vehicle can act as monitor and update the trust metric of its neighbors according to their behavior in the network. In addition, our model can be customized through different parameters like the trust interval and the number of transitions needed to reach the highest trust level. This flexibility enables to adapt the model according to the application context. The performance evaluation of the proposed model is presented with different parameters and two types of disruptive vehicles are taken into account: malicious and selfish. The obtained results show the resistance, the robustness and the incentive of the proposed model against the fluctuations of the vehicles behaviors.

In the last few years, the localization issue in wireless sensor networks has gained a lot of popularity for providing flexible and novel location-aware applications. However, throughout the variety of research works in this topic, most interests focused purely on the localization scheme itself rather than the security issue of the localization. In this paper, we propose a new and original secure version of AT-Dist, a distance-based multihop localization algorithm previously explored but under a non-adversarial environment. This version, called SecAT-Dist, proposes a lightweight security scheme that combines RC4-based hash function and symmetric encryption system to enable sensor nodes to authenticate received beacon location information and protects hop-count information from being arbitrary or selfishly changed. Furthermore, we introduce a trust model based on a set of confidence index taking benefits from specific characteristics of distance-based multihop localization algorithms. Analytically, we show that the number of trust anchors, among the total number including malicious anchors, is reduced. Simulation results show that our security scheme is more resistant to external attacks and allows great number of nodes to be located with accuracy.

We propose an efficient dynamic architecture of the Public Key infrastructure (PKI) for vehicular ad hoc networks (VANETs) based on a trust model and a novel distributed clustering algorithm. Furthermore, we introduce the notion of a VANET Dynamic Demilitarized Zone (VDDZ), composed of the set of confident vehicles located within the immediate neighborhood of each clusterhead (CH) to assume the Registration Authorities (RA). The VDDZ aims to secure the elected CAs by shielding them from unknown or malicious vehicles. A host of simulations using urban and highway scenarios are conducted to investigate the effects of the transmission range, the speed of vehicles and the number of confident vehicles in the network on the security level, the stability and the efficiency of our proposed architecture. In particular, the results show a strong dependency of the security and the stability on the assumed percentage of trust nodes and the mobility models.

In this paper, we propose a novel routing algorithm based on the network cartography which is collected using an asynchronous distributed cartography gathering algorithm. Each node senses its own dynamics and chooses locally an appropriate routing size. As such stationary nodes generate little signaling traffic, however fast moving nodes choose small routing periods to mitigate the effect of mobility. Moreover, every node integrates a self regulating process that dynamically regulates the already chosen routing period to track the timely evolution of the node dynamics. The performance of our proposed routing protocol are evaluated and compared to the known OLSR through extensive simulations. First, we show that the collected network cartography maintains over time a validity ratio above 97 percent even for high node speed. Second, while our proposed routing protocol provides around 97 percent routing validity, the OLSR can hardly deliver more than 60 percent. Third, the proposed protocol provides much more throughput than OLSR and much less end to end delay at moderate to high speeds and workloads.

In this paper, we propose a dynamic PKI for vehicular ad hoc networks aiming to distribute the role of the central certification authority (CA) among a set of dynamic chosen CAs. The election of dynamic CAs is based on a clustering algorithm where the cluster heads (CH) perform the role of CAs. The clustering process is based on both security and mobility. Furthermore, we define a new approach called the dynamic demilitarized zone (DDMZ) formed by confident nodes located at 1-hop from the CH of the same cluster and intended to perform the registration authorities (RA). Extensive simulations are conducted to evaluate the performance of our clustering algorithm and to investigate the impact of transmission range, speed of vehicles and inter vehicles distances on the stability of the security infrastructure.

The intrinsic characteristics of ad hoc networks, such as the frequent connectivity changes and the strict bandwidth and power constraints, impose further challenges, especially for routing tasks. Besides, existing routing algorithms devoted to ad hoc networks and based on proactive or reactive schemes suffer from scalability due to their intrinsic mechanisms. The control overhead induced by routing packets is a primary factor, since it increases with the number of nodes, especially in large and dense networks evolving in a dynamic environment. Relying on a virtual infrastructure seems a promising approach to overcome the scalability problem. The basic idea consists on assigning additional tasks to a limited set of dominating nodes, satisfying specific requirements. In this paper, we present a routing algorithm, which exploits the benefits of our clustering algorithm TBCA. Conducted simulations show the ability of our new approach to reduce the control overhead and improve the reactivity of routing to the topology changes.

In a dynamic network environment under heavy traffic load, shortest-path routing algorithms, particularly attempt to adapt to traffic changes, frequently exhibit oscillatory behaviors and cause performance degradation. In this paper, we first analyze, the instability factors and their results in the multicast infrastructure, and then analyze the solutions leading to stability in switched networks. Subsequently, we propose a solution to the above routing problem, where the route computation is based on the actual load on the network links. We propose a fast and simple heuristic algorithm named the Cost-Delay Shortest Path (CDSP) algorithm, which attempts to strike a balance between the different QoS parameters. The CDSP algorithm is based on a simple path exponential selection function taking simultaneously both the cost and delay into consideration and allowing the network load to be distributed in an optimal way.

Extending system lifetime by effectively managing power on participating nodes is critical in wireless ad hoc networks. Recent work has shown that, by appropriately powering off nodes, energy may be significantly saved. The IEEE 802.11 protocol specifies a simple power save mechanism (PSM) to conserve energy. Data frames are advertised during a fixed period of time, known as an ATIM window, at epochs known as beacon intervals. However, the announcement traffic puts a heavy constraint on the size of both the ATIM period and the beacon interval and consequently on throughput, end to end delay and power saving. In this paper, we address this problem by proposing the use of carrier sensing during the ATIM window to reduce the number of exchanged announcement frames. Carrier sensing is used as an energy efficient method to let nodes know if their neighbors are Awake. We propose two new protocols (the BTA-PSM and the UTA-PSM), derived from the PSM. These protocols try to enhance PSM's performances by inferring from the already advertised future behaviors of the neighboring nodes of a given mobile station. Simulation results testified to the superiority of BTA-PSM and UTA-PSM over PSM and the Dynamic Carrier Sense PSM (DCS-PSM) in ensuring greater power saving, higher throughput and lower delay.

The fulfilment of guaranteed multiple criteria based quality of service (QoS) for multimedia applications servicing multiple subscribers is known to be a NP complete problem. Moreover, finding the multicast graph respecting the defined QoS requirements and minimizing network resources is also a NP-complete optimization task. The well-known greedy algorithm Mamcra, proposed in the literature, computes the set of shortest paths from a source to all destination, and then reduces this set to an efficient set of multicast routes, without compromising the requested level of QoS. A closer look at Mamcra shows that it does not exploit further simple but possible reductions of the multicast sub-graph. In this paper, we propose a taboo search algorithm, named TabooQMR, that is augmented by some meta-heuristics to improve the multicast sub-graph computed by the greedy algorithm Mamcra, and leading to a considerable improvement, as demonstrated by the simulation results.

Designing power aware protocols becomes a pre-requisite to conserve energy and extend network life time. In fact, many target applications may require such features when being deployed for long periods in hostile environments, such as rescue or military operations. To assure power saving while preserving network capacity, relaying on a virtual backbone seems a promising approach. Through keeping a subset of nodes active for communication tasks, we allow other nodes to switch to sleep mode reducing consequently energy waste. However, the benefits of clustering come at a cost in terms of time and the prohibitive overhead incurred during the clusters' establishment and maintenance. In this paper, we investigate the influence of the underlying clustering algorithm on the performance of a power saving mechanism. The conducted simulations confirm the importance given to the choice of an efficient clustering algorithm to achieve energy efficiency while preserving network capacity.

Nowadays large scale data storage and processing can be achieved on a set of federated computers which can be interconnected over a LAN (local area network), a cluster or even a grid. Many researchers attempted to achieve this work on volunteer grids where the corresponding computers are voluntary connected or disconnected. In fact, this kind of grids presents several advantages such as the possibility of the simultaneous utilization of the corresponding computers by different users or/and applications. The big challenge of such grids is how to guarantee to their users the trust and the required security. In this paper, we show how identity federation based on agent technology can be exploited to deal with this mentioned challenge.

Wireless distributed systems (WDS) for IEEE 802.11 WLANs are gaining popularity as an effective mean to extend the network coverage area. However, the use of just one wireless channel restricts their efficiency. In this paper, we propose to use a multi-interface WDS to enhance its performance. We investigate two different scheduling policies the sequencing enforced policy (SEP) and the sequencing relaxed policy (SRP) which depend on whether packet sequencing is enforced within the WDS or rather re-established at its edge. For each policy, we investigated two different, yet very simple scheduling algorithms, the round robin and the random uniform algorithms, to dictate the selection of the interfaces. We show that both policies provide tangible improvements. Conducted simulations show, in particular, that the SRP results in almost doubling the network throughput when using just two interfaces per access point. The SRP policy along with the RR algorithm outperforms the SEP policy though it requires a resequencing action at the edge of the WDS. The end to end delays and the re-sequencing buffer sizes are also evaluated.

Multimedia applications are expected to guarantee end-to-end quality of service (QoS) and are characterized by stringent constraints on delay, delay-jitter, bandwidth, cost, etc. In the litterature, we observe that Kruskal's algorithm is limited to minimal (maximal) spanning unconstrained tree. In this paper, we extend Kruskal's algorithm to incorporate the delay bound constraint. Consequently, we propose a novel algorithm, called EKRUS (Extended Kruskal), for constructing multicast trees. The EKRUS' distinguishing features consists in a better management of Kruskal's priority queues, and in the provision of edge priority aggregation. Preliminary results show that our proposed EKRUS algorithm performs as good as the best well-known algorithms (such as the DDMC, DMCTc algorithms) while exhibiting better complexity. Furthermore, we believe that EKRUS is well suited to actual implementation in networks requiring support for multicast communication.

Routing in mobile ad hoc networks (MANETs) is central to their proper functioning. Mobility in such networks makes the routing a real challenging task. Routes validity plays a central leveraging mission to enhance network performances. Forwarding through incorrect routes not only results in traffic wandering inside the network without ever being able to be delivered to their ultimate destinations but also over consumes valuable network resources. As mobility of nodes gets higher, the routing period should be set smaller to be able to correctly track frequent changes in the topology. An adequate trade off should then be found between the size of the routing period which controls the amount of traffic overhead and the validity of routes which governs the performances of the network. In this paper, we propose a distributed algorithm to collect the network cartography. We study the validity of the network cartography as a function of time, load and mobility. This cartography is then used to dynamically and locally self regulate the routing period size in a way to lower the routing overhead and to maximize the routing pertinence. Simulation results show that our proposed scheme tracks correctly changes in the network dynamics and properly adjusts the current routing period size.

Proactive routing in MANETs induces high signaling overhead. Increasing the routing period size, while it reduces such an overhead, prevents to correctly track frequent changes in the topology and impacts the validity of routing as time goes farther from the start of the routing period. Routes' validity plays a central leveraging mission to enhance network performances as forwarding through incorrect routes not only results in traffic wondering inside the network without ever being able to be delivered to their ultimate destinations but also over consumes valuable network resources. In this paper, we propose an autonomic self tuning approach to dynamically gauge the size of the routing period in a way to properly calibrate between the amount of signaling overhead and the routing validity to yield better performances. First, we propose a distributed algorithm to collect the network cartography. We then study the validity of this cartography as a function of time and mobility. The validity of the cartography is then used to dynamically and locally self regulate the routing period size in a way to calibrate the signaling overhead and the routing pertinence. Simulation results show that our proposed scheme not only is capable of correctly tracking changes in network dynamics but also outperforms conventional proactive algorithms by doubling the network throughput at moderate to high workloads.

We first propose a new proactive routing framework based on probabilistic decisions and a generic model to compute the existence probabilities of nodes and links. Then, we present a distributed algorithm to collect the cartography of the network. This cartography is used to instantiate the existence probabilities. Conducted simulations show that our proposal yields substantially better routing validity. Nonetheless, it amounts to much longer routes. We proposed then a bounding technique to overcome this side effect and defined two probabilistic proactive routing variants. Conducted simulations show that our proposed bounded probabilistic proactive routing schemes outperform conventional routing protocols and yield up to 66 percent increase in throughput.

Different re-authentication methods have been proposed to reduce the time needed to complete a handover. If the handover latency is an important criterion, network operators have to take into account a lot of parameters while designing their networks, such as signaling overhead, functional properties or deployability. In this paper, a comparison of several 802.11 re-authentication method signaling overheads is given. Three methods have been evaluated thanks to a mathematical model, which integrates the size of all messages necessary to achieve complete authentications and re-authentications.

Due to their mobility, stations in ad hoc networks are equipped with autonomous batteries providing limited resources of energy. Thus power conservation proves to be a paramount factor to increase the network lifespan. A closer look at the mechanism of IEEE 802.11 PSM and all its numerous derivative proposals enables us to see some room for further improvements especially for large and dense cluster based networks. This paper presents an optimization of the functional properties of PSM to improve its energy conservation without changing or requiring additional control or management frames, yet it contributes to the betterment of all PSM derivatives especially for those based on a dynamic announcement window such as the Dynamic Carrier Sense DCS-PSM. PSM specifies that a station must announce its traffic before. The announcement traffic puts a heavy constraint on the size of both the ATIM period and the beacon interval and consequently on throughput, end to end delay and power saving. The proposed Neighborhood Aware Power Saving Mechanisms (NA-PSM and NTA-PSM) aim at reducing the number of exchanged announcement frames in order to increase the throughput and decrease both power consumption and delay. Simulation results testified to the superiority of NTA-PSM over PSM and the Dynamic Carrier Sense PSM (DCS-PSM) in ensuring greater power saving, higher throughput and lower delay.

The well-known greedy multicast routing algorithm Mamcra, proposed in the literature, computes the set of shortest paths from a source to all destinations, and then reduces this set to an efficient set of multicast routes, without compromising the requested level of QoS. In this paper, we propose a taboo search algorithm, named TabooQMR, that is augmented by some meta-heuristics to improve the multicast sub-graph computed by the greedy algorithm Mamcra, leading to a considerable improvement, as demonstrated by the simulation results.

This paper describes a new approach for routing in Mobile Ad Hoc Networks that is based on the concept of polymorphic behavior. This approach combines the benefits of proactive routing and probabilistic routing in time in a periodic manner in order to get the best of each approach at the appropriate

Different fast re-authentication methods have been proposed to reduce the secure handover latency in 802.11 networks. Fast re-authentication methods perform proactive distribution of authentication keys avoiding authentication exchanges during network re-entry. The efficiency of these methods depend

In 4G networks, various wireless access technologies will be integrated into a heterogeneous network based on an IP core network infrastructure. Thus, numerous works focus on mobility and vertical handover management to allow multiple-interfaces mobile terminals to roam seamlessly between these access networks. The different handoff schemes can be classified into three approaches according to where the decision to handoff is made: within the terminal, the network or thanks to a collaboration between them. However, these approaches still present some drawbacks; namely the problem of resource management whenever the handover is controlled by the mobile terminal (MT) and the problem of scalability and complexity whenever the handover is rather decided by the network. In this paper, we propose a new approach that explicitly takes into account management requirements, the current resource usage and user preferences. Furthermore, our solution provides means to select the "best-suited" network for each application according to its expectations in terms of QoS. A feasibility study of our solution is then conducted on a single mobile terminal by using typical scenarios and applying various algorithms to evaluate their behaviors.

Traditional IP multicast has been proposed in order to manage group communications over the Internet in a bandwidth efficient manner. Although this proposition has been well studied, there are still some problems for its deployment. In this paper, we propose a new algorithm mQMA that deals with two important problems of traditional IP multicast, i.e., multicast forwarding state scalability and multi-constrained QoS routing. The algorithm mQMA builds few trees and maintains few forwarding states for the groups thanks to the technique of multicast tree aggregation, which allows several groups to share the same delivery tree. Moreover, the algorithm mQMA builds trees satisfying multiple QoS constraints. We show, trough extensive simulations, that mQMA leverages the same QoS performances as Mamcra which is the main multi-constrained multicast routing algorithm. Moreover, mQMA reduces dramatically the number of trees to be maintained.

Many broadcasting protocols have been proposed to broadcast multimedia streams over broadband networks. These protocols are focusing on minimizing both the server and the network bandwidth and the client waiting time. While a special interest was given to these two criteria, only few works have discussed the implementation aspects of these protocols. An efficient broadcasting protocol proved analytically as optimal in terms of bandwidth consumption and waiting time minimization, should also take into account the implementation aspects. In this paper, we present a new proactive broadcasting protocol to deploy in an IP network. We show, through a comparative study, that our protocol slightly outperforms the theoretically most efficient known protocol.

The proliferation of new distributed application raises new requirements in term of communication functionalities such as group communication and quality of service handling. After a description of multicast services in ATM networks, we present an extension of the ATM multicast service to support multicast sessions with both dynamic and heterogeneous quality of service. Our proposed approach is based on integrating at the ATM switches QoS handling processes along with the required signalling procedures required to handle members join and leave in such environment.

Summary form only given. This paper aims to prove through an analytical study that even a loosely coupled architecture such as a grid computing can be used to support an effective multiagent system in many ways especially to speedup the dynamic time warp algorithm (DTW) for Arabic printed cursive OCR. The adaptation of the (DTW) algorithm to Arabic printed cursive OCR provides excellent recognition rate without a prior characters segmentation especially for some font sizes (16, 18, and 20). Experiments show that the DTW algorithm is able to recognize perfectly Arabic printed cursive characters by the use of a references library formed only of isolated characters (one occurrence per character). The major problem of the DTW is the slowness of its response time because of the enormous amount of computation to achieve. Multiagent systems (MAS) are very flexible and are considered to be a very attractive framework to support distributed applications, performance evaluation of the proposed MAS shows that the task granularity is one of the key performance parameters that can govern the number of agents to use and the achievable speedup. We found in particular that if the amount of computation achieved by the MAS is greater 2 times than the maximum amount of communication and synchronization required by any two agents (of the MAS) then the proposed MAS is effective.

Summary form only given. New emergent distributed multimedia applications require end-to-end quality of service (QoS) guarantees and have stringent constraints on delay, jitter, cost, etc. Taking into account such needs in IP networks stands of utmost necessity. MPLS and traffic engineering provide indeed an adequate mean to establish constrained routes which satisfy application requirements especially in terms of bandwidth and delay. These routes are computed by running a QoS algorithm on the traffic engineering database maintained by an extended IGP routing protocol. In this paper, we first study and analyze three known QoS algorithms, namely SPF-TE, WSPF and DORA. This study is done through very detailed simulations using ONS, a simulator of the OSPF protocol, recently developed and integrated into the well known NS simulator. We show that while all these algorithms outperform clearly SPF, the algorithm usually used within OSPF, DORA algorithm stands slightly better than the two others. Then, we propose three different potential improvements of DORA and propose a new QoS algorithm termed WDORA that incorporates one these improvements. We show that WDORA outperforms DORA for different performance metrics.

Video on demand (VoD) is a multimedia service which allows a remote user to select and then view video at his convenience at any time he wants. A VoD system is usually intended to provide VCR-like functions and capabilities. Required bandwidth and latency time, defined as user waiting time, are the most critical issues in VoD systems. While the majority of previous works have focused on minimizing the required bandwidth and the latency time, little attention has been given to interactivity handling. Interactive solutions propose either a very limited interactivity or require a server intervention to handle VCR operations, leading to an additional use of bandwidth. We describe a new broadcast protocol, named discrete interactive staggered broadcasting, DISB. This protocol treats interactivity through local-client resources, regardless of the number of downloading channels used. The evaluation of the DISB protocol is conducted through an analytical study. This study shows the DISB client buffer behavior, the client waiting time when performing a jump forward operation, the limit of a fast forward one and how DISB performs comparing to other staggered broadcasting protocols.

Speech is the most natural and widespread form of human communication. That is why speech synthesis has interested researchers for decades. It turns out that developing an unlimited text-to-speech system is an enormous task. The traditional methods (synthesis by rule and synthesis by concatenation of pre-recorded sounds) used for this have not given good results. In such a situation, neural networks (NNs) have the potential to give better results thanks to their property of interpolation and their capacity of generalisation. We present a synthesis system for the Arabic language. The choice of parameters which will be used to drive the NN is very important and have an effective influence on the quality of produced speech. Work has been done to evaluate different methods based on linear predictive coding; the resulting speech was machine-like and not intelligible. We suggest to use CELP to drive the NN, which provides high quality speech.

Text-to-speech synthesis is of great interest and its applications are several. For this reason, it has interested many researchers for decades. Two methods are usually used: synthesis by rule and synthesis by concatenation of pre-recorded sounds. But these methods have some disadvantages such as difficulty to be adapted to a new speaker or to a new language. Recently, neural networks (NN) have been used with nonconventional problems where a traditional solution seems impossible. Text-to-speech appears as one of these problems. In this field, it has been shown that NN don't work well when they are directly fed with speech samples. Therefore, works have been done to explore and evaluate different parametric forms of speech based on linear predictive coding (LPC), used for training, and found that LSP produced the best results. However, these methods don't take into account residual signal and speech produced was machine-like and not natural. We propose in this paper to drive the NN with codebook-excited linear prediction (CELP), which provides high quality speech, to perform Arabic speech synthesis.

A mobile stationless multi-hop packet radio network consists of a set of mobile and geographically distributed nodes (e.g., computers, terminals, etc., equipped with radio units), called packet radio units (PRUs), which communicate using a shared broadcast radio channel without a central station control. In this paper we consider the routing in highly mobile stationless multi-hop packet radio networks, We provide a validation of the use of the tier-ring architecture, and we present a scheme for handling mobile packet radio units in stationless environment by the use of a link-traversal approach when a node (packet radio unit) is no longer in possession of an outgoing link to communicate with the rest of the network.