Some aspects of traffic control and performance evaluation of ATM networks

The emerging high-speed Asynchronous Transfer Mode (ATM) networks are expected to integrate through statistical multiplexing large numbers of traffic sources having a broad range of statistical characteristics and different Quality of Service (QOS) requirements. To achieve high utilisation of network resources while maintaining the QOS, efficient traffic management strategies have to be developed. This thesis considers the problem of traffic control for ATM networks. The thesis studies the application of neural networks to various ATM traffic control issues such as feedback congestion control, traffic characterization, bandwidth estimation, and Call Admission Control (CAC). A novel adaptive congestion control approach based on a neural network that uses reinforcement learning is developed. It is shown that the neural controller is very effective in providing general QOS control. A Finite Impulse Response (FIR) neural network is proposed to adaptively predict the traffic arrival process by learning the relationship between the past and future traffic variations. On the basis of this prediction, a feedback flow control scheme at input access nodes of the network is presented. Simulation results demonstrate significant performance improvement over conventional control mechanisms. In addition, an accurate yet computationally efficient approach to effective bandwidth estimation for multiplexed connections is investigated. In this method, a feed forward neural network is employed to model the nonlinear relationship between the effective bandwidth and the traffic situations and a QOS measure. Applications of this approach to admission control, bandwidth allocation and dynamic routing are also discussed. A detailed investigation has indicated that CAC schemes based on effective bandwidth approximation can be very conservative and prevent optimal use of network resources. A modified effective bandwidth CAC approach is therefore proposed to overcome the drawback of conventional methods. Considering statistical multiplexing between traffic sources, we directly calculate the effective bandwidth of the aggregate traffic which is modelled by a two-state Markov modulated Poisson process via matching four important statistics. We use the theory of large deviations to provide a unified description of effective bandwidths for various traffic sources and the associated ATM multiplexer queueing performance approximations, illustrating their strengths and limitations. In addition, a more accurate estimation method for ATM QOS parameters based on the Bahadur-Rao theorem is proposed, which is a refinement of the original effective bandwidth approximation and can lead to higher link utilisation

Integration Protocols for Voice and Data Traffic

Increasing demands for multimedia services offer integration of multimedia traffic as a hot issue in the future research areas. As a result, in the literature, many multiplexing schemes have been proposed. However, most of them have been implemented with a high complexity, others may be non-effective to satisfy the multiplexing performance criteria, while the rest are still not subjected to a wide range of analysis. Therefore, there is a critical need for comparing some of the recommended multiplexing schemes as well as developing a simple and effective integration protocol while still achieving reasonable bandwidth utilization. This thesis is intended to examine integration protocols for multimedia traffic, with primary focusing on voice-data integration. Firstly, a survey of the existing multiplexing schemes and related issues are presented. Next, an Adaptive Round Robin (ARR) protocol is proposed, as an alternative for voice-data integration, and extensively simulated. Finally, further comparisons, based on computer simulations, are carried out for various multiplexing schemes including Strictly Priority Servicing (SPS), Fixed Round Robin (FRR), Dynamic Bandwidth Allocation/(T1, T2) and Queue Length Threshold (QLT).As a contribution of the thesis, the proposed protocol tries to avoid the drawbacks of the previous multiplexing schemes besides satisfying the multiplexing performance criteria. The protocol differs from the others in that, it gives a limited priority for voice over data, it organizes the incoming packets to the single First-in First-out (FIFO) output buffer rather than the only outgoing scheduling, i.e., all data sources are polled in order according to the adaptation policy; however, before a data source can send a packet, all active voice sources are polled in order. Thus it provides an improvement in voice delay performance without significant effect on data delay performance over previous protocols. In addition, simulation comparisons between various multiplexing schemes have been discussed. In these simulations voice packets are assumed to be generated from on-off sources (talkspurt-silence calls), which is closer to reality and which is not considered in most of the performance analyses of previous schemes

Application of Visual Simulation in Communication Systems

A communications system is a collection of individual communications networks, transmission systems, relay stations, tributary stations, and data terminal equipment (DTE) usually capable of interconnection and interoperation to form an integrated whole. The components of a communications system serve a common purpose, are technically compatible, use common procedures, respond to controls, and operate in unison. A typical communication link includes, at a minimum, three key elements: a transmitter, a communication medium (or channel), and a receiver. The ability to simulate all three of these elements is required in order to successfully model any end-to-end communication system. In order to achieve this target we have used a simulation software “VisSim” ,or Visual Simulator ,that allows us to use a graphical approach to simulation and modeling. With graphical programming, the diagram is the source code, depicted as an arrangement of nodes connected by wires. Each piece of data flows through the wires, to be consumed by nodes that transform the data mathematically or perform some action such as I/O. The visual simulator allows us to model end-to-end communication systems at the signal or physical level. We use VisSim/ Comm to build both transmitter and receiver models, filters and equalizers, as well as channel models and coding techniques from a first principles perspective, by selecting and connecting predefined blocks. In this project work we simulate a variety of models including analog, digital and mixed mode designs, and quickly simulate their behavior using the VisSim/Comm software and graphical programming

COSSAP simulation model of DS-CDMA indoor microwave ATM LAN

This thesis presents an original work in the area of designing and implementing a simulation testbed for modelling a high speed spread spectrum Asynchronous Transfer Mode (ATM) Local Area Network (LAN). The spread spectrum technique used in this LAN model is Direct Sequence Code Division Multiple Access (DS-CDMA). The simulation model includes at least a physical layer of such a LAN, embedded into the COSSAP1 simulation environment, and has been fully tested. All the newly developed building blocks are comprised of standard blocks from the COSSAP libraries or compatible user-built primitive blocks (only where it is absolutely necessary), and are flexible enough to allow the modification of simulation or model parameters; such as the number of signal channels, modulation method used, different spreading code sequences and so on. All these changes can be made with minimal effort. Another significant contribution made in this thesis is the extended research into evaluating the Bit Error Rate (BER) performance of different spread spectrum COMA coding schemes for an indoor microwave A1M LAN [8]. Different spread spectrum CDMA coding schemes are compared for their transmission error rate in Additive White Gaussian Noise (AWGN) channel with varying transmitted signal power and at different channel Signal to Noise Ratio (SNR) levels. Since a wireless microwave channel is very prone to transmission errors, a major contribution of the simulation testbed developed in this thesis is its use in the finding of an optimal physical layer transmission scheme with the best Bit Error Rate (BER) performance in an indoor environment

Study of modulation techniques for multiple access satellite communications

Multiple access communication utilizing small ground stations for satellite communication modulation - multiplexing technique

Performance analysis of an asynchronous transfer mode multiplexer with Markov modulated inputs

Ankara : Department of Electrical and Electronics Engineering and the Institute of Engineering and Science of Bilkent University, 1993.Thesis (Ph.D.) -- Bilkent Iniversity, 1993.Includes bibliographical references leaves 108-113.Asynchronous Transfer Mode (ATM) networks have inputs which consist of superpositions of correlated cell streams. Markov modulated processes are commonly used to characterize this correlation. The first step through gaining an analytical insight in the performance issues of an ATM network is the analysis of a single channel. One objective of this study is the performance analysis of an ATM multiplexer whose input is a Markov modulated periodic arrival process. Based on the transient behavior of the nD/D/1 queue, we present an approximate method to compute the queue length distribution accurately. The method reduces to the solution of a linear differential equation with variable coefficients. Another general traffic model is the Markov Modulated Poisson Process (MMPP). We employ Pade approximations in transform domain for the deterministic service time distribution in an M MPP/D/1 queue so as to compute the distribution of the buffer occupancy. For both models, we also provide algorithms for analysis in the case of finite queue capacities and for computation of effective bandwidth.Akar, NailPh.D

Satellite Data Communications Link Requirements for a Proposed Flight Simulation System

The purpose of this study was to investigate the requirements necessary for data and voice communication via satellite, linking Embry-Riddle Aeronautical University (ERAU) and other flight training facilities. The proposed research was conducted following a descriptive method of collecting information, generating and analyzing data, and listing the results for the proposed link requirements. The current fiber-optic communications link at ERAU in Daytona Beach was presented to establish a general foundation of communications. Research was done into methods used by satellite common carriers for realistic data and calculations. A proposed data link to connect flight simulators at the ERAU Prescott campus with the air traffic control simulation facilities at the ERAU Daytona Beach campus was developed. Data link requirements based on this scenario were gathered and the final assessment was presented. A suggested method of implementing this proposal, including carrier service and equipment selection, was developed and further research into expanding this proposal into a network was suggested