Ghassen Ben Brahim

Topology Control Schema for Better QoS in Hybrid RF/FSO Mesh Networks

The practical limitations and challenges of radio frequency (RF) based communication networks have become increasingly apparent over the past decade, leading researchers to seek new hybrid communication approaches. One promising strategy that has been the subject of considerable interest is the augmentation of RF technology by Free Space Optics (FSO), using the strength of each communication technology to overcome the limitations of the other. In this article, we introduce a new scheme for controlling the topology in hybrid Radio-Frequency/Free Space Optics (RF/FSO) wireless mesh networks. Our scheme is based on adaptive adjustments to both transmission power (of RF and FSO transmitters) and the optical beam-width (of FSO transmitters) at individual nodes, with the objective of meeting specified Quality of Service (QoS) requirements, specifically end-to-end delay and throughput. We show how one can effectively encode the instantaneous objectives and constraints of the system as an instance of Integer Linear Programming (ILP). We demonstrate that the technique of Lagrangian Relaxation (LR), augmented with iterative repair heuristics, can be used to determine good (albeit sub-optimal) solutions for the ILP problem, making the approach feasible for mid-sized networks. We make the proposed scheme viable for large-scale networks in terms of number of nodes, number of transceivers, and number of source-destination pairs by solving the ILP problem using a Particle Swarm Optimization (PSO) implementation.

A dynamic resource allocation scheme for delay-constrained multimedia services in CDMA 1/spl times/EV-DV forward link

CDMA2000 1/spl times/EV-DV has been proposed as one of the global standards of third-generation (3G) networks, which adopts TDM/CDM and adaptive modulation and coding (AMC) techniques to enhance the data rate. The current CDMA2000 1/spl times/EV-DV standard specifies all possible combinations of system parameters, but there is no any further specification in the standard on how to dynamically change the system parameters to support the quality-of-service (QoS) requirements imposed by the upper-layer applications. In the meantime, one of the major deficiencies of previous research work done in this area is that they all are based on the channel models of physical layer such as Rayleigh model, which is unable to capture the link-layer QoS parameters such as queueing delay. Since the dynamic resource allocation usually resides in the data link layer, a wireless channel model at the link layer would be desirable to handle the QoS requirements. In this paper, we develop a dynamic resource allocation scheme using the effective capacity link model to support delay-bounded multimedia services in CDMA2000 1/spl times/EV-DV networks. Extensive simulations have been set up and the simulation results show that the proposed dynamic resource allocation scheme significantly improves the delay and throughput performance for all types of application traffic with various QoS requirements.

A Model for Cooperative Mobility and Budgeted QoS in MANETs with Heterogenous Autonomy Requirements

Modern mobile ad-hoc networks (MANETs) frequently consist of nodes which exhibit a wide range of autonomy needs. This is particularly true in the settings where MANETs are most compelling, i.e. battlefield, response & rescue, and contexts requiring rapid deployment of mobile users. The time-critical nature of the underlying circumstances frequently requires deployment of both manned and unmanned nodes, and a coordination structure which provides prioritized tasking to them. Unlike consumer MANETs, these settings bring with them a common group purpose, making inter-node cooperation plausible. In this paper, we focus on how cooperation can improve MANET communications. We begin by taxonomizing all prior approaches and noting that no existing approach adequately captures networks where nodes exhibit a wide range of autonomy with respect to their mobility. To this end we present a new cooperative mobility model, developing a cost- benefit framework which enables us to explore the impact of cooperation in MANETs where nodes are, to varying extents, willing to move for the common good. In the second half of the paper, we describe the design of CoopSim, a platform for conducting simulation experiments to evaluate the impact of parameter, policy and algorithm choices on any system based on the proposed model. Finally, we present a small but illustrative case study and use the experimental evidence derived from it to give an initial evaluation of the merits of the proposed model and the efficacy of the CoopSim software.

A new AMC scheme for QoS provisioning in cdma2000 1xEV-DV networks

cdma2000 1xEV-DV has been proposed as one of the standards for the next generation multimedia wireless generation (MWG) systems, which adopts new techniques such as adaptive modulation and coding (AMC) schemes to enhance wireless data services. Although many possible combinations of system parameters have been specified in the current 1xEV-DV standard, there is no further specification on how to dynamically choose the optimal combination of system parameters, such as the number of Walsh codes, the number of time slots, the modulation scheme, and the channel data rate, according to variations of buffer usage and channel quality. In this paper, we first review the latest cdma2000 1xEV-DV standard focusing on its unique features. Then, we propose a new delay-bounded dynamic resource allocation scheme for the QoS provisioning in cdma2000 1xEV-DV networks. The proposed scheme supports dynamic resource allocation by selecting the optimal combination of system parameters to satisfy the QoS requirements imposed by user applications, based on not only the channel quality but also the queue length. Simulation results show the proposed resource allocation scheme can provide delay-bounded services to multimedia applications such as voice and video

A new Hybrid Genetic Variable Neighborhood search heuristic for the Vehicle Routing Problem with Multiple Time Windows

The Vehicle Routing Problem (VRP) is a known optimization problems falling under the category of NP-Hard set of problems. VRP, along with its variations, continue to be extensively explored by the research community due to their large domain of application (environment, agriculture, industry, etc.) and economic impact on improving the overall performance, Quality of Services and reducing the operational cost. In this paper, we focus on VRPMTW; a variant of VRP with Multiple Time Windows constraints. We introduce a novel Hybrid Genetic Variable Neighborhood Search (HGVNS) based heuristic for the optimization of VRPMTW. The proposed framework uses genetic cross-over operators on a list of best parents and new implementations of local search operators. Computational results on benchmark data show substantial performance improvement when using the newly introduced heuristic.

Determining vulnerability resolution time by examining malware proliferation rates

One of the ways that malware infects is by exploiting weaknesses in computer systems, often through conditions in software. When this happens, software and operating system vendors must repair these vulnerabilities by patching their software. However, vendors can release patches but cannot force users to apply them. Malware attempts to proliferate without regard to the state of the infected system; it is only once that the malware infection is stopped that we can truly say that systems are patched to eliminate that exploit. By examining appearance and disappearance of malware types, as determined through dynamic analysis of malware samples, classified by behavioral profiles correlated with a timeline of discovery dates, we can determine a more real-world average time for effective patch times, as opposed to the time it takes for a vendor to release a patch for a discovered vulnerability.

Using MapReduce and hierarchical entropy analysis to speed-up the detection of covert timing channels

Covert timing channels provide a mechanism to transmit unauthorized information across different processes. Applications that generate large datasets allow this information to be easily hidden within the big data, making it difficult to detect. In this paper, we introduce the application of big data analysis techniques, specifically MapReduce, in the process of speeding up the performance of covert time channels detection. The hierarchal entropy algorithm (HEA) is utilized to reveal a “needle” of covert timing channels from a huge “haystack” of inter-arrival times. A real indexed inter-arrival dataset of approximately 1.4 gigabyte is generated between two different machines and injected by 615 bytes of covert timing message. The HEA with MapReduce was able to uncover around 7*10−6 of hidden covert message from this huge amount of data in a significantly shorter time as compared to the classical sequential HEA.

Feature Extraction and Large Activity-Set Recognition Using Mobile Phone Sensors

Diese Arbeit beschaftigt sich mit dem Problem der Aktivitatserkennung unter Verwendung von Daten, die vom Mobiltelefon des Benutzers erhoben wurden. Wir beginnen mit der Betrachtung und Bewertung der Beschrankungen der gangigen Aktivitatserkennungsansatze fur Mobiltelefone. Danach stellen wir unseren Ansatz zur Erkennung einer grosen Anzahl von Aktivitaten vor, welche die meisten Nutzeraktivitaten abdeckt. Auserdem werden verschiedene Umgebungen unterstutzt, wie zum Beispiel zu Hause, auf Arbeit und unterwegs. Unser Ansatz empfiehlt ein einstufiges Klassifikationsmodell, dass die Aktivitaten genau klassifiziert, eine grose Anzahl von Aktivitaten umfangreich abdeckt und in realen Umgebungen umsetzbar anzuwenden ist. In der Literatur gibt es keinen einzigen Ansatz, der alle drei Eigenschaften in sich vereint. In der Regel optimieren vorhandene Ansatze ihre Modelle entweder fur einen oder maximal zwei der folgenden Eigenschaften: Genauigkeit, Umfang und Anwendbarkeit. Unsere Ergebnisse zeigen, dass unser Ansatz ausreichende Leistung im Hinblick auf Genauigkeit bei einem realistischen Datensatz erbringt, trotz deutlich erhohter Aktivitatszahl im Vergleich zu gangigen Modellen, die auf Aktivitatserkennen basieren.

Security-by-construction in web applications development via database annotations

Huge amounts of data and personal information are being sent to and retrieved from web applications on daily basis. Every application has its own confidentiality and integrity policies. Violating these policies can have broad negative impact on the involved companys financial status, while enforcing them is very hard even for the developers with good security background. In this paper, we propose a framework that enforces security-by-construction in web applications. Minimal developer effort is required, in a sense that the developer only needs to annotate database attributes by a security class. The web application code is then converted into an intermediary representation, called Extended Program Dependence Graph (EPDG). Using the EPDG, the provided annotations are propagated to the application code and run against generic security enforcement rules that were carefully designed to detect insecure information flows as early as they occur. As a result, any violation in the datas confidentiality or integrity policies is reported. As a proof of concept, two PHP web applications, Hotel Reservation and Auction, were used for testing and validation. The proposed system was able to catch all the existing insecure information flows at their source. Apart from the proof of concept and to comprehensively test the performance of our system, we compared it to JLift, a state-of-the-art type-based system approach to detect information leaks. Both approaches were run against custom made PHP web applications and publicly available applications downloaded from SourceForge and GitHub. The results show that our approach outperforms JLift in terms of accuracy and the number of false alarms, and is able to catch the insecure flows at their source when they first occurred.

MOLSR: Mobile-agent based optimized Link State Routing Protocol

The popularity of Mobile Ad Hoc networks (MANETs) continues to increase due to the technological advances in wireless radios and wireless networks. Given the unpredictability of the wireless medium, one of the major challenges in MANETs remains to be the efficiency of the underlying routing protocol. The Optimized Link State Routing Protocol (OLSR) is one of the most popular routing protocols being deployed in MANETs. OLSR uses multipoint relay mechanism (MPR) to maintain the topology information at each node. Instead of using blind broadcasting where each node sends a control message to all its neighbors, and consequently every neighbor forwards the message to its neighbors, MPR selects a small set of nodes to do the broadcasting such that all network nodes are covered. In this paper, we propose improving further the performance of OLSR by introducing the concept of Mobile Agent (MA) when maintaining the MANET topology information, resulting in MA-based OLSR (MOLSR). In MOLSR, MA will substitute MPR and will rely on message unicast instead of broadcast, a major improvement to current OLSR in terms of traffic overhead. In MOLSR, every node creates and launches a MA that intelligently travels the network and returns with the full topology. In case of an MA loss, MOLSR automatically recovers the MA and makes sure it covers the whole network. Extensive simulation results show that MOLSR outperforms OLSR in various areas, namely the total control messages, network utilization, and reliable message transfer.