1,721,031 research outputs found
Modeling the internet congestion controlas a time delay system: A robust stability analysis
No full textIn this paper control theoretic analysis is employed to model the Internet flow and congestion control as a time delay system. It is shown that the self-clocking principle, which is known to be a key component of the Transmission Control Protocol (TCP), corresponds to implement a simple proportional controller (P) plus a Smith predictor (SP). It is also shown that different variants of the TCP congestion control algorithms, such as classic TCP Reno or the recent Westwood TCP, can be modelled by proper input shaping of the reference signal. Finally, the robustness of the control algorithm in the face of uncertain round trip time delay is analysed
Nonlinear observer design to synchronize hyperchaotic systems via a scalar signal
No full textIn this brief control theory is used to formalize hyperchaos synchronization as a nonlinear observer design issue, Following this approach, a new systematic tool to synchronize a class of hyperchaotic systems via a scalar transmitted signal is developed, The proposed technique has been applied to synchronize two well-known hyperchaotic systems
A system theory approach for designing cryptosystems based on hyperchaos
No full textIn this paper a general methodology for designing chaotic and hyperchaotic cryptosystems is developed. The basic idea is to make the decrypter a nonlinear observer for the state of the encrypter. Referring to this concept, some propositions are given which enable the plaintext to be retrieved if proper structural properties of the chaotic system hold. The proposed tool proves to be powerful and flexible, since a wide class of cryptosystems can be designed by exploiting different chaotic and hyperchaotic circuits. The advantages of the suggested approach are illustrated in detail. In particular, the utilization of hyperchaos-based cryptosystems, as well as the increased complexity of the transmitted signal, make a contribution to the development of communication systems with higher security
Synchronization of high-order oscillators by observer design with application to hyperchaos-based cryptography
No full textThe aim of this paper is to make a contribution in the context of both hyperchaos synchronization and cryptography. The approach illustrated herein, which exploits the concept of observer from system theory, is at first applied for synchronizing via a scalar signal two recent examples of high-order oscillators, characterized by several positive Lyapunov exponents. Successively, an example of hyperchaos-based cryptography is illustrated. The advantages of the proposed tool are discussed in detail. In particular, the utilization of both synchronization of complex dynamics and cryptography seems to make a contribution to the development of communication systems with higher security
Synchronizing hyperchaotic systems by observer design
No full textIn this brief, a technique for synchronizing hyperchaotic systems is presented. The basic idea is to make the driven system a linear observer for the state of the drive system. By developing this approach, a linear time-invariant synchronization error system is obtained, for which a necessary and sufficient condition is given in order to asymptotically stabilize its dynamics at the origin. The suggested tool proves to be effective and systematic in achieving global synchronization. It does not require either the computation of the Lyapunov exponents, or the initial conditions belonging to the same basin of attraction. Moreover, it guarantees synchronization of a wide class of hyperchaotic systems via a scalar signal. Finally, the proposed tool is utilized to design a secure communications scheme, which combines conventional cryptographic methods and synchronization of hyperchaotic systems. The utilization of both cryptography and hyperchaos seems to make a contribution to the development of communication systems with higher security
Mathematical Analysis of Westwood+ TCP Congestion Control
No full textTCP congestion control is based on an additive-increase/multiplicative-decrease (AIMD) probing paradigm aimed at adapting the sending rate of TCP data sources to match the Internet timevarying available bandwidth. Westwood+ TCP has been recently proposed to improve the tracking of available bandwidth of classic TCP. It is based on an end-to-end estimate of the available bandwidth, which is obtained by properly counting and filtering the stream of acknowledgement
packets. The estimate is used to adaptively decrease the congestion window and slow start threshold after congestion so that it can be said that Westwoodþ TCP substitutes the classic multiplicative decrease with an adaptive decrease paradigm. The authors propose a mathematical analysis of the
additive-increase=adaptive-decrease (AIADD) paradigm to analyse the steady-state throughput provided by Westwood+ TCP and investigate the intra-protocol fairness of the AIADD paradigm and the inter-protocol friendliness between AIADD and AIMD algorithms. It is shown that (i) both classic and Westwoodþ TCP provide a throughput that is proportional to 1/sqrt(p), where p is the
segment drop probability, that is they are friendly to each other; and (ii) the throughput of Westwoodþ TCP is proportional to 1/sqrt(RTT), where RTT is the round trip time, whereas the throughput of Reno TCP is proportional to 1/RTT, i.e. Westwood+ TCP improves the intra-protocol fairness. Finally, Ns-2 simulations are reported in order to validate the mathematical model in the
presence of a wide range of network loads, loss probabilities and round trip times
Controlling chaotic dynamics using backstepping design with application to the Lorenz system and Chua's circuit
No full textIn this Letter backstepping design is proposed for controlling chaotic systems. The tool consists in a recursive procedure that combines the choice of a Lyapunov function with the design of feedback control. The advantages of the method are the following: (i) it represents a systematic procedure for controlling chaotic or hyperchaotic dynamics; (ii) it can be applied to several circuits and systems reported in literature; (iii) stabilization of chaotic motion to a steady state as well as tracking of any desired trajectory can be achieved. In order to illustrate the general applicability of backstepping design, the tool is utilized for controlling the chaotic dynamics of the Lorenz system and Chua's circuit. Finally, numerical simulations are carried out to show the effectiveness of the techniqu
Synchronisation of hyperchaotic oscillators using a scalar signal
No full textA method is presented for synchronising two recent examples of hyperchaotic oscillators via a scalar transmitted signal. The approach, based on linear control theory, is simple and rigorous. It does not require either the computation of the Lyapunov exponents or initial conditions belonging to the same basin of attraction
Synchronizing high dimensional chaotic systems via eigenvalue placement with application to cellular neural networks
No full textIn this paper a method for synchronizing high dimensional chaotic systems is developed. The objective is to generate a linear eri or dynamics between the master and the slave systems, so that synchronization is achievable by exploiting the controllability property of linear systems. The suggested approach is applied to Cellular Neural Networks (CNNs), which can be considered as a tool for generating complex hyperchaotic behaviors. Numerical simulations are carried out for synchronizing CNNs constituted by Chua's circuits
Intraprotocol fairness and interprotocol friendliness of TFRC congestion control algorithm
No full textThe TCP-friendly rate control (TFRC) algorithm has been proposed
for supporting applications such as video streaming or telephony over
the Internet, where a relative smooth sending rate is of importance.
The fairness and friendliness of TFRC over scenarios with multiple
congested routers is evaluated. Results obtained using the ns-2
simulator show that while TFRC improves network utilisation with
respect to Reno TCP, it exhibits a significant degree of unfairness and
unfriendliness towards Reno TCP
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