Nasser Yazdani

Mutual information-based feature selection for intrusion detection systems

As the network-based technologies become omnipresent, threat detection and prevention for these systems become increasingly important. One of the effective ways to achieve higher security is to use intrusion detection systems, which are software tools used to detect abnormal activities in the computer or network. One technical challenge in intrusion detection systems is the curse of high dimensionality. To overcome this problem, we propose a feature selection phase, which can be generally implemented in any intrusion detection system. In this work, we propose two feature selection algorithms and study the performance of using these algorithms compared to a mutual information-based feature selection method. These feature selection algorithms require the use of a feature goodness measure. We investigate using both a linear and a non-linear measure-linear correlation coefficient and mutual information, for the feature selection. Further, we introduce an intrusion detection system that uses an improved machine learning based method, Least Squares Support Vector Machine. Experiments on KDD Cup 99 data set address that our proposed mutual information-based feature selection method results in detecting intrusions with higher accuracy, especially for remote to login (R2L) and user to remote (U2R) attacks.

A Quality of Service Architecture for IEEE 802.16 Standards

A worldwide demand for a high-speed, always-on broadband wireless system across residential and business regions is emerging rapidly due to an increasing reliance on Internet for information, business and entertainment, as well as new bandwidth-intensive applications. The IEEE 802.16 air interface standard is truly a state-of-the-art specification for fixed broadband wireless access (BWA) systems employing a point-to-multipoint (PMP) architecture. Although IEEE 802.16 standards define different mechanisms to provide quality of service requirements, it is the responsibility of the developers to obtain efficient designs and thus, providing QoS in BWA systems has become a challenging issue for designers of such systems. In this paper, we introduce a novel architecture to support quality of service in IEEE 802.16 standards. Moreover, we propose a design approach to implement such architecture. Simulation result shows the high performance of our architecture for all types of traffic classes defined by the standard

An analytical model of delay in multi-hop wireless ad hoc networks

Several analytical models of different wireless networking schemes such as wireless LANs and meshes have been reported in the literature. To the best of our knowledge, all these models fail to address the accurate end-to-end delay analysis of multi-hop wireless networks under unsaturated traffic condition considering the hidden and exposed terminal situation. In an effort to gain deep understanding of delay, this paper firstly proposes a new analytical model to predict accurate media access delay by obtaining its distribution function in a single wireless node. The interesting point of having the media access delay distribution is its generality that not only enables us to derive the average delay which has been reported in almost most of the previous studies as a special case but also facilitates obtaining higher moments of delay such as variance and skewness to capture the QoS parameters such as jitters in recently popular multimedia applications. Secondly, using the obtained single node media access delay distribution, we extend our modeling approach to investigate the delay in multi-hop networks. Moreover, probabilities of collisions in both hidden and exposed terminal conditions have been calculated. The validity of the model is demonstrated by comparing results predicted by the analytical model against those obtained through simulation experiments.

Improving performance of transport protocols in multipath transferring schemes

One major drawback of multipath transferring schemes inspired by usage of different paths with diverse delays is the emergence of reordering among packets of the same flow. In this paper, we present two separate approaches to resolve this problem for UDP and TCP connections. By properly scheduling the packets among multiple paths, our UDP-based approach tries to deliver data to the receiver in-order, while imposing a minimum possible delay and small buffer space on the receivers application. We theoretically prove the optimality of the proposed method and then present its analytical results. Unfortunately, in the case of TCP, the reordering intensifies the problem by bringing more timeouts and many unnecessary fast-retransmits which eventually degrades the throughput of TCP connections considerably. To address these issues, we first present the general conditions that should be held to avoid timeouts in multipath schemes. Then, we enhance our approach by preventing nonessential fast-retransmit/recovery events in TCP. Moreover, we introduce an analytical model to estimate the probability of triggering 3rd duplicate ACK in our method. Finally, through simulation experiments we show that the performance of our multipath methods is comparable with the optimal one-path transmissions (with aggregated bandwidth); especially, in terms of throughput and fast-retransmit ratio parameters.

Improved algorithms for leader election in distributed systems

An important challenge confronted in distributed systems is the adoption of suitable and efficient algorithms for coordinator election. The main role of an elected coordinator is to manage the use of a shared resource in an optimal manner. Among all the algorithms reported in the literature, the Bully and Ring algorithms have gained more popularity. In this paper, we describe novel approaches towards improving the Bully and Ring algorithms and also propose the heap tree mechanism for electing the coordinator. The higher efficiency and better performance of our presented algorithms with respect to the existing algorithms is validated through extensive simulation results.

Efficient construction of network topology to conserve energy in wireless ad hoc networks

Wireless ad hoc networks are usually composed of battery constraint devices, which make energy conservation a vital concern of their design. Reducing energy consumption has been addressed through different aspects till now. Topology Control (TC) is a well-known approach which tries to assign transmission ranges of nodes to optimize their energy utilization while keeping some network properties like connectivity. However, in current TC schemes, the transmission range of each node is mostly accounted as the exclusive estimator for its energy consumption, while ignoring the amount of data it sends or relays. In this paper, we redefine the problem of Topology Control regarding both transmission range and traffic load parameters. After proving the NP-hardness of the new problem, we mathematically formulate it as a mixed integer linear programming problem to find optimal solutions. Then, we introduce polynomial-time heuristic algorithms to practically solve the problem. During construction of network topology, we deliberately take into account the impact of the employed routing method on load of individual nodes. Finally, we show the advantages of our proposals through simulations.

Energy conserving movement-assisted deployment of ad hoc sensor networks

Sensor network deployment is very challenging due to hostile and unpredictable nature of usage environments. In this letter, we propose two methods for the self-deployment of mobile sensors. The first one is a randomized solution that provides both simplicity and applicability to different environments. Inspired by simulated annealing, it improves both speed and energy conservation of the deployment process. The other method is suggested for environments where sensors form a connected graph, initially. At the cost of this extra limitation, we gain considerable improvements.

Effect of the contention window size on performance and fairness of the IEEE 802.11 standard

IEEE 802.11 is a widely used standard for MAC and PHY layers of WLANs. Unfortunately, the access methods offered in this standard cannot support QoS (Quality of Service) for real-time traffics. Using multimedia applications over WLANs is increasing and, on the other hand, it seems that the access methods employed in this standard causes high variations in delay or jitter and wastes bandwidth due to collisions. There are many methods to enable DCF—basic access method in 802.11—with service differentiation and QoS. The difficulty in majority of these methods is unfair bandwidth allocation among low and high priority traffics at high loads resulting starvation for low priority traffics. In this paper, we modify the way that the CW (Contention Window) size is calculated after a successful transmission and study the effect of the CW size on performance and fairness. Results of our simulations show that the performance of DCF with this modification is better, specially, for traffics in which throughput is the most important parameter. Besides, this method provides better fairness among low and high priority traffics. We also employ a scheme to enable 802.11 with service differentiation which grants dynamic priority to low priority traffics to prevent starvation, specially, in high loads.

Chain-Based Anonymous Routing for Wireless Ad Hoc Networks

Wireless ad hoc networks are so vulnerable to passive attacks and eavesdropping adversaries due to their shared medium which makes network traffic easy to capture and analyze. Therefore, security and privacy protections are of extreme importance for protocols and applications in such networks. In this paper, we introduce a new framework for anonymous routing, named chain-based routing, to improve the privacy. In our framework, nodes on a path are virtually bound to each other like a chain. Each node is only aware of its associated links in a flow and does not require any other information about source, destination, or other parts of the chain. Based on this framework, we propose an on-demand routing protocol, called Chain-based Anonymous Routing (CAR), which uses unicast-based broadcast data transfer to fulfill anonymous communication in wireless ad hoc networks. Through hiding identifiers of nodes inside the chain, CAR realizes sender, receiver, and relationship anonymity in addition to untraceability in the network. Moreover, it is resistant to a wide range of passive attacks while adapting to implement other security mechanisms in the presence of active attacks.

Reliability-Aware Task Allocation in Distributed Computing Systems using Hybrid Simulated Annealing and Tabu Search

Reliability is one of the important issues in the design of distributed computing systems (DCSs). This paper deals with the problem of task allocation in heterogeneous DCSs for maximizing system reliability with several resource constraints. Memory capacity, processing load and communication rate are major constraints in the problem. Reliability oriented task allocation problem is NP-hard, thus many algorithms were presented to find a near optimal solution. This paper presents a Hybrid of Simulated Annealing and Tabu Search (HSATS) that uses a non-monotonic cooling schedule to find a near optimal solution within reasonable time. The HSATS algorithm was implemented and evaluated through experimental studies on a large number of randomly generated instances. Results have shown that the algorithm can obtain optimal solution in most cases. When it fails to produce optimal solution, deviation is less than 0.2 percent. Therefore in terms of solution quality, HSATS is significantly better than pure Simulated Annealing.