Tarik Taleb

A Stable Routing Protocol to Support ITS Services in VANET Networks

There are numerous research challenges that need to be addressed until a wide deployment of vehicular ad hoc networks (VANETs) becomes possible. One of the critical issues consists of the design of scalable routing algorithms that are robust to frequent path disruptions caused by vehicles mobility. This paper argues the use of information on vehicles movement information (e.g., position, direction, speed, and digital mapping of roads) to predict a possible link-breakage event prior to its occurrence. Vehicles are grouped according to their velocity vectors. This kind of grouping ensures that vehicles, belonging to the same group, are more likely to establish stable single and multihop paths as they are moving together. Setting up routes that involve only vehicles from the same group guarantees a high level of stable communication in VANETs. The scheme presented in this paper also reduces the overall traffic in highly mobile VANET networks. The frequency of flood requests is reduced by elongating the link duration of the selected paths. To prevent broadcast storms that may be intrigued during path discovery operation, another scheme is also introduced. The basic concept behind the proposed scheme is to broadcast only specific and well-defined packets, referred to as ldquobest packetsrdquo in this paper. The performance of the scheme is evaluated through computer simulations. Simulation results indicate the benefits of the proposed routing strategy in terms of increasing link duration, reducing the number of link-breakage events and increasing the end-to-end throughput.

Detecting and avoiding wormhole attacks in wireless ad hoc networks

A particularly severe attack on routing protocols in ad hoc networks is the so-called worm- hole attack in which two or more colluding attackers record packets at one location, and tunnel them to another location for replay at that remote location. When this attack targets specifically routing control packets, the nodes that are close to the attackers are shielded from any alternative routes with more than one or two hops to the remote location. All routes are thus directed to the wormhole established by the attackers. In the optimized link state routing protocol, if a wormhole attack is launched during the propagation of link state packets, the wrong link information percolates throughout the network, leading to routing disruption. In this article we devise an efficient method to detect and avoid wormhole attacks in the OLSR protocOLSR protocolol. This method first attempts to pinpoint links that may potentially be part of a wormhole tunnel. Then a proper wormhole detection mechanism is applied to suspicious links by means of an exchange of encrypted probing packets between the two supposed neighbors (endpoints of the wormhole). The proposed solution exhibits several advantages, among which are its nonreliance on any time synchronization or location information, and its high detection rate under various scenarios.

Explicit Load Balancing Technique for NGEO Satellite IP Networks With On-Board Processing Capabilities

Non-geostationary (NGEO) satellite communication systems offer an array of advantages over their terrestrial and geostationary counterparts. They are seen as an integral part of next- generation ubiquitous communication systems. Given the non-uniform distribution of users in satellite footprints, due to several geographical and/or climatic constraints, some Inter-Satellite Links (ISLs) are expected to be heavily loaded with data packets while others remain underutilized. Such scenario obviously leads to congestion of the heavily loaded links. It ultimately results in buffer overflows, higher queuing delays, and significant packet drops. To guarantee a better distribution of traffic among satellites, this paper proposes an explicit exchange of information on congestion status among neighboring satellites. Indeed, a satellite notifies its congestion status to its neighboring satellites. When it is about to get congested, it requests its neighboring satellites to decrease their data forwarding rates by sending them a self status notification signaling message. In response, the neighboring satellites search for less congested paths that do not include the satellite in question and communicate a portion of data, primarily destined to the satellite, via the retrieved paths. This operation avoids both congestion and packet drops at the satellite. It also ensures a better distribution of traffic over the entire satellite constellation. The proposed scheme is dubbed Explicit Load Balancing (ELB) scheme. While the multi-path routing concept of ELB has many advantages, it may lead to persistent packet reordering. In case of connection-oriented protocols, this phenomenon results in unnecessary shrinkage of the data transmission rate. A solution to this issue is also incorporated in the design of ELB. The interactions of ELB with mechanisms that provide different QoS by differentiating traffic (e.g., Differentiated Services) are also discussed. The good performance of ELB, in terms of better traffic distribution, higher throughput, and lower packet drops, is verified via a set of simulations using the Network Simulator (NS).

Angelah: a framework for assisting elders at home

The ever growing percentage of elderly people within modern societies poses welfare systems under relevant stress. In fact, partial and progressive loss of motor, sensorial, and/or cognitive skills renders elders unable to live autonomously, eventually leading to their hospitalization. This results in both relevant emotional and economic costs. Ubiquitous computing technologies can offer interesting opportunities for in-house safety and autonomy. However, existing systems partially address in-house safety requirements and typically focus on only elder monitoring and emergency detection. The paper presents ANGELAH, a middleware-level solution integrating both elder monitoring and emergency detection solutions and networking solutions. ANGELAH has two main features: i) it enables efficient integration between a variety of sensors and actuators deployed at home for emergency detection and ii) provides a solid framework for creating and managing rescue teams composed of individuals willing to promptly assist elders in case of emergency situations. A prototype of ANGELAH, designed for a case study for helping elders with vision impairments, is developed and interesting results are obtained from both computer simulations and a real-network testbed.

Recent trends in IP/NGEO satellite communication systems: transport, routing, and mobility management concerns

Non-geostationary (NGEO) satellite communication systems are seen as an attractive solution to realize the vision of anywhere, anytime pervasive access to the Internet. Their design and development have thus gained tremendous interest in the last few years. Commencing with a brief overview of general NGEO satellite configurations, this article next addresses the key technical difficulties in the development of NGEO IP-based satellite communications systems. The article discusses routing concerns, mobility management, and transport protocols with an emphasis on TCP performance in NGEO satellite networks. Some key innovations are presented. The recursive, explicit, and fair window adjustment (REFWA) scheme is presented as a solution to improve the efficiency and fairness of TCP in NGEO systems. An improvement to the REFWA scheme, REFWA plus, is also described to combat link errors in satellite environments.

Protocols for reliable data transport in space internet

A variety of protocols have been proposed for reliable data transport in space Internet and similar network environments. It is necessary to conduct a survey on these protocols to investigate and compare among them. In this article, we present a survey on the protocols proposed for reliable data transport in space Internet, with a focus on the latest developments. The survey includes the following contents: (1) classification of these protocols into different approaches; (2) discussions and comments on the design and operation methods of the protocols; and (3) comparisons and comments on the main techniques and performance of the protocols.

A Cross-Layer Approach for an Efficient Delivery of TCP/RTP-Based Multimedia Applications in Heterogeneous Wireless Networks

Recent trends in the telecommunication industry have been moving toward the development of ubiquitous information systems, where the provision of a plethora of advanced multimedia services should be possible, regardless of time and space limitations. An efficient and seamless delivery of multimedia services over various types of wireless networks is still a challenging task. The underlying difficulty consists of the disparity in the bandwidth availability over each network type. Indeed, the fundamental challenge upon a handoff phenomenon in a heterogeneous wireless network consists of an efficient probing of the bandwidth availability of the new network, followed by a prompt adjustment of the data delivery rate. This paper presents a cross-layer approach that involves five layers, namely, physical, data link, application, network, and transport layers. The three former layers are used to anticipate the handoff occurrence and to locate the new point of attachment to the network. Based on their feedback, the transport layer is used then to probe the resources of the new network using low-priority dummy packets. Being the most widely used protocol for multimedia delivery, this paper addresses multimedia applications based on the Transmission Control Protocol (TCP) and the Real-time Transport Protocol (RTP). The design of the whole cross-layer architecture is discussed, and enhancements to the two protocols are proposed. The performance of the enhanced TCP and the RTP are evaluated and compared against existing schemes through extensive simulations. The obtained results are encouraging and promising for the delivery of multimedia services in heterogeneous wireless networks.

An explicit and fair window adjustment method to enhance TCP efficiency and fairness over multihops Satellite networks

Transmission control protocol (TCP) is the most widely used transport protocol in todays Internet. Despite the fact that several mechanisms have been presented in recent literature to improve TCP, there remain some vexing attributes that impair TCPs performance. This paper addresses the issue of the efficiency and fairness of TCP in multihops satellite constellations. It mainly focuses on the effect of the change in flows count on TCP behavior. In case of a handover occurrence, a TCP sender may be forced to be sharing a new set of satellites with other users resulting in a change of flows count. This paper argues that the TCP rate of each flow should be dynamically adjusted to the available bandwidth when the number of flows that are competing for a single link, changes over time. An explicit and fair scheme is developed. The scheme matches the aggregate window size of all active TCP flows to the network pipe. At the same time, it provides all the active connections with feedbacks proportional to their round-trip time values so that the system converges to optimal efficiency and fairness. Feedbacks are signaled to TCP sources through the receivers advertised window field in the TCP header of acknowledgments. Senders should accordingly regulate their sending rates. The proposed scheme is referred to as explicit and fair window adjustment (XFWA). Extensive simulation results show that the XFWA scheme substantially improves the system fairness, reduces the number of packet drops, and makes better utilization of the bottleneck link.

R-MAC: Reservation Medium Access Control Protocol for Wireless Sensor Networks

As sensor nodes are subject to strict power limitations and often deployed in harsh environments, there is significant potential for a node to be hidden from another node. The impact of hidden nodes on performance of the IEEE 802.15.4 low-rate wireless personal area network protocol is evaluated. At lower Tx power, as a result of hidden nodes, there are more collisions in the network increasing the cost of packet delivery. The simulation results indicate that there exists an optimum transmission power that minimizes the impact of hidden nodes, and it depends on factors such as network load, desired throughput and beacon order. Results indicate that additional throughput gain and lower cost per packet delivered can be achieved by increasing the beacon order at higher Tx power.Energy consumption is a critical issue in wireless sensor networks as the battery of a sensor node, in most cases, cannot be recharged or replaced after deployment. In order to detect an event, a sensor node spends most of the time in monitoring its environment, during which a significant amount of energy can be saved by placing the radio in the low power sleep mode when no reception and/or transmission of data is involved. In this paper, we discuss the design of a new MAC protocol for wireless sensor networks, which mainly avoids overhearing, collisions, and frequent commutation between sleep and active modes. These issues are generally considered to be the most important reasons behind energy waste in heavy loaded conditions of wireless sensor networks. The proposed protocol, called Reservation-MAC (R-MAC), uses two separate periods during the communication process. In the first period, nodes compete for time slots reservation for their future transmissions, and in the second period, each node transmits its data or receive data from a corresponding sender. Once a node is aware of its transmission and/or reception time slot, it stays active only for these time slots and goes back to the sleep mode during the remaining time of the transmission period. In our experiments, the performance of the R-MAC protocol is studied in saturated conditions and compared with the well known S-MAC and T- MAC protocols. Depending on the traffic load, the proposed MAC protocol significantly improves the energy consumption compared to S-MAC and T-MAC.

SAT04-3: ELB: An Explicit Load Balancing Routing Protocol for Multi-Hop NGEO Satellite Constellations

Due to geographical and/or climatic constraints, the community of future satellite users will exhibit a significant variance in its density over the Globe. This density variance will yield a scenario where some satellite links are congested while others are underutilized. To ensure an intelligent engineering of traffic over satellite networks, this paper proposes a routing protocol that enables neighboring satellites to explicitly exchange information on their congestion status. A soon-to-be-congested satellite requests its neighboring satellites to decrease their data forwarding rates. In response, the neighboring satellites search for less congested paths that do not include the satellite in question and communicate a portion of data, primarily destined to the satellite, via the retrieved paths. By so doing, congestion, and the resulting packet drops, can be avoided. A better distribution of traffic among satellites can be guaranteed as well. The proposed scheme is dubbed Explicit Load Balancing (ELB) scheme. A set of simulations is conducted to evaluate the performance of the ELB scheme using the Network Simulator. In terms of Quality of Service, encouraging results are obtained: better traffic distribution, higher throughput, and lower packet drops.