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With the recent advances in the telecommunications and auto industries, we have witnessed growing interest in ITS, of which VANETs are an essential component. SDN can bring advantages to ITS through its ability to provide flexibility and programmability to networks through a logically centralized controller entity that has a comprehensive view of the network. However, as the SDN paradigm initially had fixed networks in mind, adapting it to work on VANETs requires some changes to address particular characteristics of this kind of scenario, such as the high mobility of its nodes. There has been initial work on bringing SDN concepts to vehicular networks to expand its abilities to provide applications and services through the increased flexibility, but most of these studies do not directly tackle the issue of loss of connectivity with said controller entity. In this article, we propose a hierarchical SDN-based vehicular architecture that aims to have improved performance in the situation of loss of connection with the central SDN controller. Simulation results show that our proposal outperforms traditional routing protocols in the scenario where there is no coordination from the central SDN controller. [ABSTRACT FROM PUBLISHER]

In this paper, we present an Efficient COngestion DEtection (ECODE) protocol that aims at evaluating the traffic characteristics of each road segment (i.e., the road section connecting between any two successive intersections). Moreover, ECODE efficiently and reliably detects road segments with high traffic congestion in any urban grid-layout area. The traffic situation and the congestion level of each road segment changes from time to time. Proactive, reactive, and hybrid iterative execution schemes have been proposed to execute ECODE repeatedly and to thus obtain a more real-time traffic evaluation of each road segment. These iterative execution schemes aim also at investigating the effects of several data dissemination mechanisms that are usually used to control the congestion over the communication network. ECODE is discussed and its performance is reported on and compared to previous protocols in this field; an extensive set of scenarios and experiments have been used which are in turn implemented by NS-2. From the experimental results, ECODE achieves a 30% more accurate evaluation of traffic characteristics compared to previous protocols in this field. Moreover, it consumes on average 60% of the bandwidth that was consumed by the previous protocols. Considering the iterative execution schemes of ECODE, the proactive scheme consumes 50% more bandwidth than the reactive scheme. However, the accuracy of the traffic evaluation per road segment using the reactive scheme is lower than the accuracy of the proactive scheme used for short intervals. The hybrid scheme lies between the proactive and the reactive schemes in terms of the bandwidth consumption and the accuracy of congestion level evaluation. Finally, we have used ECODE to evaluate the traffic congestion level and to investigate the traffic distribution over some main streets in the downtown area of Ottawa; this has been set up as a practical example of the application of ECODE. [ABSTRACT FROM AUTHOR]

Context awareness, intended as providing the current execution environment at the service level, is a fundamental capability in future mobile systems. Unfortunately, the real-world realization of such scenarios is currently undermined by inefficient context data delivery mechanisms, which introduce excessive overhead over bandwidth-constrained wireless fixed infrastructures. To efficiently offload context access from fixed infrastructures to mobile nodes, this paper presents a new data caching algorithm that exploits peculiar aspects of context distribution, mainly limited data lifetime and interests similarity between nodes in physical proximity, to properly select the data to evict when necessary. Our solution considers a history over past data accesses and information over data replication to better exploit the limited available space. Extensive simulation results, collected in NS2 simulator, support our assumptions and demonstrate that our caching solution improves system scalability while adding a limited management overhead. [ABSTRACT FROM AUTHOR]

Abstract: The provision of video dissemination capabilities over vehicular networks improves the service experience from users’ side for applications such as heavy traffic notification, hazard warnings and event advertisement. However, the combination of video streaming’s stringent requirements and the dynamic topology of Vehicular Ad Hoc Networks (VANETs) poses severe challenges for efficient and effective video dissemination. We propose in this work a receiver-based solution that conducts video transmissions decoupled from the relay nodes selection mechanism, namely REDEC. This solution takes advantage of the reactive nature of the receiver-based approach without incurring excessive collisions and overhead due to the transmission of videos large packets at a high frequency. We have also conducted extensive simulation experiments using variety of scenarios with different densities and data exchange rate. Our results indicate clearly that our proposed REDEC protocol outperforms other solutions and is scalable while fulfilling the end-to-end delay requirements of video streaming. Furthermore, we have observed that REDEC also offers higher video reception rates when compared to existing video streaming solutions. [Copyright &y& Elsevier]

Pore networks can be simulated in silico by using the dual site-bond Model. In this approach, a set of cavities (sites) are interconnected to each other by means of a set of throats (bonds), while considering that each site should be always larger than any of its delimiting bonds. The NoMISS greedy algorithm has been implemented recently in order to address this task; nevertheless, even if this procedure is relatively fast, there arises problems related to large memory consumption and long computing time, as pore networks become somewhat large. Here, three parallel methods are proposed to allow a proficient construction of large pore networks. The first method is a parallel Monte Carlo procedure, which applies a number of exchanges among pore sizes in order to obtain a valid pore network. The other two methods are parallel versions of the pioneering NoMISS greedy algorithm. The first version uses a static data partitioning to speed up the running time, whilst the second applies a dynamic data distribution policy to improve the pore network quality. The obtained results show the behavior of each proposed version with respect to their performance and quality, by employing the resources of a 125-core Linux cluster. [ABSTRACT FROM AUTHOR]

One of the most challenging issues facing vehicular networks lies in the design of an efficient MAC protocol due to the mobile nature of nodes and the interference associated with the dynamic environment. Moreover delay constraints for safety applications add complexity and latency requirements to the design. Existing MAC protocols overcome some challenges however don’t provide an integrated solution. Hence, the merit if this work lies in designing an efficient MAC protocol that incorporates various VANet’s challenges in a complete end-to-end solution. In this work, we propose an efficient Multichannel QoS Cognitive MAC (MQOG). MQOG assesses the quality of channel prior to transmission employing dynamic channel allocation and negotiation algorithms to achieve significant increase in channel reliability, throughput and delay constraints while simultaneously addressing Quality of Service. The uniqueness of MQOG lies in making use of the free unlicensed bands. The proposed protocols were implemented in OMNET++ 4.1, and extensive experiments demonstrated a faster and more efficient reception of safety messages compared to existing VANet MAC Protocols. Finally, improvements in delay, packet delivery ratios and throughput were captured. [ABSTRACT FROM AUTHOR]

Large scale dense Wireless Sensor Networks (WSNs) will be increasingly deployed in different classes of applications for accurate monitoring. Due to the high density of nodes in these networks, it is likely that redundant data will be detected by nearby nodes when sensing an event. Since energy conservation is a key issue in WSNs, data fusion and aggregation should be exploited in order to save energy. In this case, redundant data can be aggregated at intermediate nodes reducing the size and number of exchanged messages and, thus, decreasing communication costs and energy consumption. In this work, we propose a novel Data Routing for In-Network Aggregation, called DRINA, that has some key aspects such as a reduced number of messages for setting up a routing tree, maximized number of overlapping routes, high aggregation rate, and reliable data aggregation and transmission. The proposed DRINA algorithm was extensively compared to two other known solutions: the Information Fusion-based Role Assignment (InFRA) and Shortest Path Tree (SPT) algorithms. Our results indicate clearly that the routing tree built by DRINA provides the best aggregation quality when compared to these other algorithms. The obtained results show that our proposed solution outperforms these solutions in different scenarios and in different key aspects required by WSNs. [ABSTRACT FROM PUBLISHER]

ABSTRACT Intelligent transportation systems have attracted many researchers. These latter have invested much effort to develop many applications and services mainly for vehicular systems. Services can be classified as safety or convenience services. A service discovery mechanism is needed to permit the discovery and the interaction with the existing services. However, so far security issues for service discovery in vehicular systems have not been widely considered, mainly for the convenience type of applications. Thus, a secure service discovery and communication protocol is necessary to prevent from many attacks and malicious processes in the vehicular system. In this paper, we investigate the possible attacks that can occur during the service discovery and communication processes. Then, we present our proposed group-based authentication scheme for secure service discovery and communication in vehicular systems. Our proposed scheme is mainly dedicated for the convenience type of applications. We discuss the security requirements achieved by our proposed protocol and we report on its performance evaluation. We prove through our extensive set of simulations that our proposed scheme achieves a high success rate for the secure discovery of services, while maintaining the scalability of the network and low discovery delays. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We consider sensor networks where the sensor nodes are attached on entities that move in a highly dynamic, heterogeneous manner. To capture this mobility diversity we introduce a new network parameter, the direction-aware mobility level, which measures how fast and close each mobile node is expected to get to the data destination (the sink). We then provide local, distributed data dissemination protocols that adaptively exploit the node mobility to improve performance. In particular, “high” mobility is used as a low cost replacement for data dissemination (due to the ferrying of data), while in the case of “low” mobility either (a) data propagation redundancy is increased (when highly mobile neighbors exist) or (b) long-distance data transmissions are used (when the entire neighborhood is of low mobility) to accelerate data dissemination toward the sink. An extensive performance comparison to relevant methods from the state of the art demonstrates significant improvements, i.e. latency is reduced by even four times while keeping energy dissipation and delivery success at very satisfactory levels. [Copyright &y& Elsevier]

In recent years, we have witnessed an increasing interest in deploying wireless sensor networks (WSNs) for real-life applications. However, before WSNs become a commodity, several challenging issues remain to be resolved. Object-tracking sensor network (OTSN)-based applications are widely viewed as being among the most interesting applications of WSNs. OTSN is mainly used to track certain objects in a monitored area and to report their location to the application's users. However, OTSNs are well known for their energy consumption when compared with other WSN applications. In this paper, we propose a prediction-based tracking technique using sequential patterns (PTSPs) designed to achieve significant reductions in the energy dissipated by the OTSNs while maintaining acceptable missing rate levels. PTSP is tested against basic tracking techniques to determine the appropriateness of PTSP under various circumstances. Our experimental results have shown that PTSP outperforms all the other basic tracking techniques and exhibits significant amounts of savings in terms of the entire network's energy consumption. [ABSTRACT FROM PUBLISHER]

Abstract: Dynamic balancing of computation and communication load is vital for the execution stability and performance of distributed, parallel simulations deployed on the shared, unreliable resources of large-scale environments. High Level Architecture (HLA) based simulations can experience a decrease in performance due to imbalances that are produced initially and/or during run time. These imbalances are generated by the dynamic load changes of distributed simulations or by unknown, non-managed background processes resulting from the non-dedication of shared resources. Due to the dynamic execution characteristics of elements that compose distributed applications, the computational load and interaction dependencies of each simulation entity change during run time. These dynamic changes lead to an irregular load and communication distribution, which increases overhead of resources and latencies. A static partitioning of load is limited to deterministic applications and is incapable of predicting the dynamic changes caused by distributed applications or by external background processes. Therefore, a scheme for balancing the communication and computational load during the execution of distributed simulations is devised in a scalable hierarchical architecture. The proposed balancing system employs local and cluster monitoring mechanisms in order to observe the distributed load changes and identify imbalances, repartitioning policies to determine a distribution of load and minimize imbalances. A migration technique is also employed by this proposed balancing system to perform reliable and low-latency load transfers. Such a system successfully improves the use of shared resources and increases distributed simulations’ performance by minimizing communication latencies and partitioning the load evenly. Experiments and comparative analyses were conducted in order to identify the gains that the proposed balancing scheme provides to large-scale distributed simulations. [ABSTRACT FROM AUTHOR]

Collaborative Virtual Environments (CVEs) such as military training programs, emergency preparedness simulations, and online games place strict requirements on network performance when participating users share the 3D virtual environment through their mobile devices in an ad hoc network. However, most support systems for existing CVEs are confined to a desktop setting, thus preventing collaboration while users are mobile. In this work, we propose and evaluate a Gnutella peer-to-peer network over mobile ad hoc networks (MANETs) to support Mobile Collaborative Virtual Environment (MCVE) applications. Both architectures share some common features such as decentralization, self-reorganization, and self-healing. However, peer-to-peer networks and MANETs operate on different network layers, and thus, cause poor performance. To address this problem, we explore a novel cross-layer approach to improve the overall performance of CVEs over MANETs. The network layer should be aware of the user's physical position in the virtual environment (VE) in order to minimize network traffic and cope with a moderate workload between nodes. In this paper, we present a cross-layer approach model for collaborative virtual environment over MANET. We describe its implementation and evaluate its performance using NS2 simulator. [ABSTRACT FROM AUTHOR]

With the rapidly growing popularity of mobile ad hoc networks (MANETs), many security concerns have arisen from this type of network. In particular, malicious nodes will jeopardize the security of mobile networks if the issues of secure data exchange are not handled properly. Encryption cannot fully protect the data communicated between nodes, as routing information may expose the identities of the communicating nodes and put their relationships at risk. In this paper, we propose an efficient anonymous routing protocol that uses a mobile agent paradigm for MANETs, which we refer to as ARMA. In our protocol, we take advantage of a trust system to prevent effectively the misbehavior of malicious nodes so that only trustworthy nodes are allowed to participate in communications. Furthermore, we present the Malicious Encryption and Malicious ID attacks, as well as other attacks, and note how our scheme is robust to them. Through the proof of protocol correctness, our protocol is analyzed to show how it offers provable security properties. Finally, we provide its performance evaluation based on simulation experiments implemented in an ns-2 simulator. Compared to the secure distributed route construction protocol (SDAR) protocol, our experimental results demonstrate that our scheme not only achieves the necessary anonymity in wireless and mobile networks, but also provides more security with reasonably little additional overhead. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract-Data Distribution Management (DDM) is one of the most critical component of any large-scale interactive distributed simulation systems. The aim of DDM is to reduce and control the volume of information exchanged among the simulated entities (federates) in a large-scale distributed simulation system. In order to fulfill its goal, a considerable amount of DDM messages needs to be exchanged within the simulation (federation). The question of whether each message should be sent immediately after it is generated or held until it can be grouped with other DDM messages needs to be investigated further. Our experimental results have shown that the total DDM time of a simulation varies considerably depending on which transmission strategy is used. Moreover, in the case of grouping, the DDM time depends on the size of the group. In this paper, we propose a novel DDM approach, which we refer to as Adaptive Grid-based (AGB) DDM. The AGB protocol is distinct from all existing DDM implementations, because it is able to predict the average amount of data generated in each time step of a simulation. Therefore, the AGB DDM approach controls a simulation running in the most appropriate mode to achieve a desired performance. This new DDM approach consists of two adaptive control parts: 1) the Adaptive Resource Allocation Control (ARAC) scheme and 2) the Adaptive Transmission Control (ATC) scheme. The focus of this paper is on the ATC scheme. We describe how to build a switching model to predict the average amount of DDM messages generated and how the ATC scheme uses this estimation result to optimize the overall DDM time. Our experimental results provide a clear evidence that the ATC scheme is able to achieve the best performance in DDM time when compared to all existing DDM protocols using an extensive set of experimental case studies. [ABSTRACT FROM AUTHOR]

Abstract: Data distribution management (DDM) plays a key role in traffic control for large-scale distributed simulations. In recent years, several solutions have been devised to make DDM more efficient and adaptive to different traffic conditions. Examples of such systems include the region-based, fixed grid-based, and dynamic grid-based (DGB) schemes, as well as grid-filtered region-based and agent-based DDM schemes. However, less effort has been directed toward improving the processing performance of DDM techniques. This paper presents a novel DDM scheme called the adaptive dynamic grid-based (ADGB) scheme that optimizes DDM time through the analysis of matching performance. ADGB uses an advertising scheme in which information about the target cell involved in the process of matching subscribers to publishers is known in advance. An important concept known as the distribution rate (DR) is devised. The DR represents the relative processing load and communication load generated at each federate. The DR and the matching performance are used as part of the ADGB method to select, throughout the simulation, the devised advertisement scheme that achieves the maximum gain with acceptable network traffic overhead. If we assume the same worst case propagation delays, when the matching probability is high, the performance estimation of ADGB has shown that a maximum efficiency gain of 66% can be achieved over the DGB scheme. The novelty of the ADGB scheme is its focus on improving performance, an important (and often forgotten) goal of DDM strategies. [Copyright &y& Elsevier]

Abstract: This paper considers the problem of self-diagnosis of wireless and mobile ad hoc networks (MANETs) using the comparison approach. In this approach, a network (MANET) consists of a collection of n independent heterogeneous mobile or stationary hosts interconnected via wireless links, and it is assumed that at most of these hosts are faulty. In order to diagnose the state of the MANET, tasks are assigned to pairs of hosts and the outcomes of these tasks are compared. The agreements and disagreements between the hosts are the basis for identifying the faulty ones. The comparison approach is believed to be one of the most practical fault identification approaches for diagnosing hard and soft faults. We develop a new distributed self-diagnosis protocol, called Dynamic-DSDP, for MANETs that identifies both hard and soft faults in a finite amount of time. The protocol is constructed on top of a reliable multi-hop architecture. Correctness and complexity proofs are provided and they show that our Dynamic-DSDP performs better, from a communication complexity viewpoint, than the existing protocols. We have also developed a simulator, that is scalable to a large number of nodes. Using the simulator, we carried out a simulation study to analyze the effectiveness of the self-diagnosis protocol and its performance with regards to the number of faulty hosts. The simulation results show that the proposed approach is an attractive and viable alternative or addition to present fault diagnosis techniques in MANET environments. [Copyright &y& Elsevier]

Abstract: In recent years, we have witnessed a growing interest in high performance computing (HPC) using a cluster of workstations. This growth made it affordable to individuals to have exclusive access to their own supercomputers. However, one of the challenges in a clustered environment is to keep system failure to the minimum and to achieve the highest possible level of system availability. High-Availability (HA) computing attempts to avoid the problems of unexpected failures through active redundancy and preemptive measures. Since the price of hardware components are significantly dropping, we propose to combine both HPC and HA concepts and layout the design of a HA–HPC cluster, considering all possible measures. In particular, we explore the hardware and the management layers of the HA–HPC cluster design, as well as a more focused study on the parallel-applications layer (i.e. FT-MPI implementations). Our findings show that combining HPC and HA architectures is feasible, in order to achieve HA cluster that is used for High Performance Computing. [Copyright &y& Elsevier]

Abstract: Coverage is an important issue related to WSN quality of service. Several centralized/decentralized solutions based on geometry information and under the assumption of disk sensing range have been introduced in the literature. However, disk sensing range assumption is too strong in the real world and cannot be held in scenarios requiring high accuracy, such as the emergency preparedness class of applications. This paper proposes a new intersection point method (IPM) that extends the disk sensing range assumption to an irregular simple polygon assumption. A unit circle test method has also been devised in order to provide a controllable degree of accuracy in the determination of fully covered nodes. By adjusting the radius r u of this unit circle test, the algorithm can be made tolerant to holes of a certain size which makes the solution flexible when the degree of accuracy must be controlled. IPM performance was evaluated through a set of simulation experiments implemented in the NS-2 simulator, which were compared to the results obtained using the central angle method (CAM) proposed by D. Tian and N.D. Georganas, and the association sponsors method (ASM) proposed by A. Boukerche, X. Fei and Regina B. Araujo. The results show that under the simple polygon sensing range assumption, our solution can efficiently identify fully covered sensors, discover holes (blind points) and archive better quality results than CAM and ASM. The performance and flexibility of IPM makes it a potential solution for applications that require a high rate of coverage with controllable hole tolerance. [Copyright &y& Elsevier]

Abstract: One of the challenges for 3D multiuser virtual simulation environments (3DMUVEs) developers is to keep the shared virtual simulation environment synchronized among all the participating users’ terminals. Support to 3DMUVEs through traditional client–server communication model offers simpler management but can lead to bottlenecks and higher latencies. Peer-to-peer communication model, on the other hand, offers no central coordination but are more complex to manage. Current peer-to-peer networks, such as KaZaA and Gnutella, provide multimedia sharing services but do not support multiuser 3D virtual environment (VE) applications. This paper describes a solution to support 3DMUVEs in a hybrid peer-to-peer Gnutella network, which provides session control and distributed shared VE synchronization. As a result of this work, two components specified by the ongoing multiuser extension to the MPEG-4 standard were implemented and integrated to the Gnutella network for control and synchronization. This solution minimizes the disadvantages of client–server and pure peer-to-peer models. The results show that this approach can be a feasible solution, specially for spontaneous 3DMUVEs that can emerge from any user, with no investment needed (apart from his own computer). The use of peer-to-peer networks such as the Gnutella could be used as a test environment for companies wishing to check both their multiuser 3DMUVEs software for correctness and their acceptance by the users community before making heavy investments. [Copyright &y& Elsevier]

Abstract: Collaborative and distributed simulation environments that span across large interconnection networks, such as the Internet, are a promising way of supporting applications distributed over multiple computing sites. How-ever, communication-intensive distributed applications may suffer from variable communication delays, jitter, and latency experienced over the network. We term a loosely coupled domain the combination of multiple sites connected through an internetwork. In this paper, we focus on large-scale distributed simulations based upon local time warp deployed over several sites connected through an interconnection network (a loosely coupled domain). We propose and study a mechanism to tune elaboration according to varying communication performances, to reduce resource consumption and rollback costs that result from unpredictable network behavior. The mechanism is composed of two parts that operate in a completely distributed way: a local elaboration rate control and a message flow control. The experimental study is conducted through emulation to exert a control on injected delays. Our results show that the mechanism is able to globally tune the entire simulation, so as to reduce the escalation of allocated computational resources and the cost of rollbacks. As delays disappear, the mechanism allows elaboration to resume normal rate. [Copyright &y& Elsevier]

Recent advances in wireless data communications tech nology have spawned an increasing demand for various types of services over wireless and wireline networks. As a result, we are witnessing an explosive growth of research and development efforts in the field of wireless and personal communication systems (PCS). Parallel simulation techniques have been investigated in studies to decrease the execution times of PCS simulations. In this paper, we present a partitioning algorithm for SWiMNet, a two-stage PCS parallel simulation testbed which makes use of a conservative scheme at Stage 1, and Time Warp at Stage 2. The partitioning algorithm focuses on statically distributing the load of the simu lation evenly in order to decrease the rollback overhead in Stage 2. The algorithm is based on an estimation of the loads involved by the model components. This paper discusses the algorithm, its implementation on a work station cluster, and the performance results of the simu lation of a real suburban area serviced by an FCA-based PCS network. The results are compared with a round- robin partitioning algorithm. The results show that the investigated partitioning algorithm can achieve a re duction of up to 60% in the rollback message overhead. [ABSTRACT FROM PUBLISHER]

The article focuses on the Quality of Service (QoS) routing policies and their effectiveness in heterogeneous wired and wireless networks. It explores routing algorithms which will take into account the dynamic change of communication networks and discuss their advantages and drawbacks when compared to traditional solutions. It stresses on the integration of QoS which focuses on a tutorial-based approach and on the evolution of routing decisions applied in heterogeneous networks that may include the load level traffic patterns and topology of the network changes the routing policy adapts for the chosen router.