Journal of Computer and Robotics
Volume:3 Issue: 2, Summer and Autumn 2010

Recently, Peer-to-Peer (P2P) networks contribute to a large fraction of the Internet backbone traffic. Consequently, misusing such networks for malicious purposes is a potential side effect. In this review article, we investigate different techniques of misusing P2P overlay networks to launch large-scale next-generation Distributed Denial of Service (DDoS) attacks. In particular, we investigate representative systems of the structured (Overnet), unstructured (Gnutella) and hybrid (BitTorrent) P2P overlay networks. Real world experiments indicate the high performance, difficulty in detection and tracking, and the low cost of launching such attacks.

The establishment as well as the survival of mobile ad-hoc networks relies on the cooperation of nodes for performing network operations such as routing and packet forwarding. In these networks, misbehaving nodes can severely degrade network’s performance by not cooperating in networking operations. In this paper, we study the issue of node misbehavior in packet forwarding. To counter this type of misbehavior, we propose a scheme based on the overhearing of MAC-layer acknowledgements. Our main idea centers on the exploitation of the fact that the impartial nodes within the intersection of the transmission zones of the ACK-transmitter and its successor overhear the transmitted acknowledgments by these two nodes. Therefore, if an ACK-transmitter emits an ACK for an in-transit packet, but on a timeout, no ACK is sensed from its successor, acknowledging the receipt of the packet, the misbehavior of the ACK-transmitter will be noticed by the impartial overhearing nodes and reported to the original data packet transmitter, i.e. to the node preceding the ACK- transmitter. We have conducted a series of NS-2 simulation experiments to evaluate the performance of our scheme.

Providing a high-quality service for transmission and playing real-time voice conversations (voice streaming) over wireless ad-hoc networks is no mean feat. Buffering together with adjusting the playout time of the packets is a receiver-side solution to overcome this challenge. In this paper, a new adaptive playout adjustment algorithm is proposed to stream the voice conversations over wireless ad-hoc networks. This algorithm always tries to be aware of the network's conditions, adapts itself with these conditions and adjusts the playout time of the voice packets as efficiently as possible. It is required that not only most of the packets be received before their playout time, as scheduled in the receiver, but also that the playout time not be too long so as to adversely affect the interactivity between the sender and the receiver. The main features of the presented method are: adjusting the threshold adaptively with respect to the varying conditions of the network in order to determine the state of system; calculating the mean network jitter dynamically based on the current conditions of the network in order to calculate the playout delay for the current packet; being optimistic about the future state of the network and not using the delay history in order to calculate the mean network delay. Simulation results show that the proposed algorithm adapts itself with the network's dynamics and adjusts the playout delay for voice packets better than the other algorithms.

Simultaneous estimation of the range and the angle of close emitters usually requires a multidimensional search. This paper proposes an algorithm to improve the position of an element for arrays designed on the basis of some certain or random rules. In the proposed method, one element moves along the same previous direction, maintaining its vertical distance from each source, to reach a constellation with less Cramer-Rao Bound (CRB). The efficiency of this method has been demonstrated through simulation and a comparative study has been conducted, contrasting both the CRB and the determinant of the received signal’s covariance matrix before and after applying our proposed scheme.

Modern integrated circuits consist of millions of standard cells and routing paths. In nano-scale designs, mis-prediction is a dominant problem that may diminish the quality of physical design algorithms or even result in the disruption of the convergence of the design cycle. In this paper, a new planning methodology is presented in which a master-plan of the chip is constructed at the early levels of the physical design, preparing for the operation of the subsequent physical design stages. As a proof of concept study, the proposed planning design flow is applied to both wire planning and buffer resource planning, and the outcomes are compared against conventional contributions. Experimental results reveal considerable improvements in terms of performance, timing yield and buffer usage.

The increasing diversity in packet-processing applications together with the rapid increase in channel bandwidth has brought about greater complexity in communication protocols. Also influenced by these factors is the computational load for packet-processing engines, demanding high performance microprocessor designs as an indispensable solution. This paper reports on extensive simulation experiments carried out for exploring the performance of instruction-level parallel Very Long Instruction Word (VLIW) processors executing packet- processing applications. On the grounds of the experimental results, a design space exploration has been used to derive an efficient application-specific VLIW processor architecture based on the VEX instruction set architecture. The VEX simulator toolset has been used for design space exploration, and a number of networking applications have been chosen to serve in guiding the architectural exploration. The optimization measures achieve up to 60% improvement in performance for the most representative packet-processing applications.

This paper undertakes the synthesis of a logic-based switching H2/H∞ state-feedback controller for continuous-time LTI singular perturbation systems. Our solution achieves a minimum bound on the H2 performance level, while also satisfying the H∞ performance requirements. The proposed hybrid control scheme is based on a fuzzy supervisor managing the combination of two controllers. A convex LMI-Based formulation of two fast and slow subsystem controllers leads to a structure which ensures a good performance in both transient and steady-state phases. The stability analysis leverages on the Lyapunov technique, inspired from the switching system theory, to prove that a system with the proposed controller remains globally stable in the face of changes in configuration (controller).

In recent years, sub-band speech recognition has been found useful in addressing the need for robustness in speech recognition, especially for the speech contaminated by band-limited noise. In sub-band speech recognition, the full band speech is divided into several frequency sub-bands, with the result of the recognition task given by the combination of the sub-band feature vectors or their likelihoods as generated by the corresponding sub-band recognizers. In this paper, we draw on the notion of discrete wavelet transform to divide the speech signal into sub-bands. We also make use of the robust features in sub-bands in order to obtain a higher sub-band speech recognition rate. In addition, we propose a likelihood weighting and fusion method based on the wavelet thresholding technique. The experimental results indicate that the proposed weighting methods for likelihood combination and classifiers fusion improve the sub-band speech recognition rate in noisy conditions.