Submitted in partial fulfillment for the Masters in Engineering Degree: Electrical Engineering, Department of Electrical Engineering, Durban University of Technology, Durban, South Africa, 2017. / All-optical networks (AON) based optical burst switching (OBS) promise to be the ultimate backbone network technology solution for next generation( NG) as well as fu­ ture generation (FG)networks because of their relatively higher resources utilization, great flexibility at lower cost and potential massive bandwidth capacities both at trans­ mission and switching levels. By design, buffering is not provisioned in interior nodes. End users exchange data with one another through end-to-end light channels, called lightpaths in which wavelength continuity is maintained. In practice, their establish­ ing, in a cost effective manner remains an inescapable challenge. The routing and wave­ length assignment (RWA) problem entices successful establishment of a physical route for each lightpath connection request, assigning a wavelength to each route and at the same time ensm·ing end to end continuity, subject to the limited number of wave­ lengths. The wavelengths must be assigned such that no lightpaths can share the same wavelength simultaneously on a given fibre, or else contentions may occur. Some data bursts may be discarded whenever contention occurs among multiple bursts that arrive simultaneously at any interior node using the same wavelength and are intended for the same output port. Because of the buffer-less nature of OBS networks, conten­ tion/congestion in the core network can quickly lead to degradation in overall network performance at moderate to high traffic levels due to heavy burst loses. In this disser­ tation we propose and evaluate a congestion management approach we refer to as '"en­ hanced congestion management" which gears towards rendering and guaranteeing a consistent QoS as well as rational and fair use of available network links. Simulation results show that the scheme can effectively minimize both contention and congestion and at the same time improving both throughput and effective utilization under mod­ erate to high network traffic loads / M

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A single user deconcentrator is designed for a circuit switched digital switching system which emphasizes mass conferencing. The switching system consists of distributed concentrators which include a first level of conferencing and a broadcast bus which includes a second level of conferencing. The deconcentrator features volume adjustment of individual conferences as well as a third and last level of conferencing- a conference of the individual conferences obtained from the broadcast bus. The design identifies the MSI and SSI components of the deconcentrator and provides an estimate of timing and board size. An alternative volume adjustment algorithm and the extension of a single user deconcentrator to a multi-user deconcentrator is discussed.

This paper architecturally describes the switching portion of a digital communications system that is dedicated to conferencing. The basic ideas and methods of circuit switching and packet switching are introduced. The conferencing function is described, and some resulting design considerations are discussed. The architecture of the switch is then presented. Circuit switching techniques are used throughout the architecture of the switch, coupled with arithmetic processing to accomplish the conferencing function. The architecture is developed in such a way that it is expandable in all directions to meet a given set of requirements. The requirements include the number of users the system supports and the number of conference channels provided. The processing stages of the switch can be sized based on these requirements and the chosen component speeds. The basic timing of each stage is given to describe its operation and establish the critical delay paths. The resulting switching methods first introduced. The switch is also tested to see if it fits the criteria for being a distributed processing system. It is concluded that if the provision for dynamic reconfiguration is added, the switch fits the criteria. Finally, further topics of study are suggested.

This thesis is mainly a survey of optical devices used in optical logic and optical space, time and frequency division switching. These are mainly optical logic devices, optical switches, optical switching matrices, optical memories and optical wavelength multiplexers and demultiplexers and optical wavelength shifters. The devices are based on a variety of operating principles and are implemented with a variety of technologies. The basic principles and technologies are described together with typical performance parameters. The different devices and technologies are compared, and areas of possible improvements indicated. As an application of this survey, the possibility of implementing optical logic circuits and an optical time-division switch for Sonet based transmission systems is discussed. / Master of Science

Data link control, multiple access, and flow control for data communication have at last advanced to the state that it is possible for applications that require combining these techniques to be carried out. Therefore, research efforts are now beginning to focus on the performance of these applications, rather than the previous trend of carrying out the performance of each scheme separately. This study analyses the performance of a Very Small Aperture Terminal (VSAT) satellite star network. The network uses roll-call polling as its multiple access scheme, High-level Data Link Control or HDLC, and go-back-N Automatic Repeat Request, for error control. The network is a VSAT packet-switched network, that carries out its communications task on a Time Division Multiplexing (TDM) satellite channel. This research consists of three major parts. First, the performance analysis of the single-hop star architecture network is carried out. This includes the study of a polling communication system for the inbound, VSAT-to-Hub line. The time delay of a packet using the inbound line is evaluated. Secondly, the performance analysis of the TDM outbound Hub-to-VSAT line is represented. The throughput of the multiplexed system for the outbound Hub-to-VSAT line, as well as the average time delay of a packet are determined. Thirdly, both the analysis of the inbound, and outbound lines are combined to provide the performance of the double-hop architecture of the network. The time delay of a VSAT-to-VSAT packet is found. / Master of Science

The main focus of the thesis is to derive stability criteria for networked control system (NCS) models featuring imperfections such as time-varying and constant delays, quantization, packet dropouts, and non-uniform sampling intervals. The main method of proof is based on matrix algebra, as opposed to methods using Lyapunov functions or integral quadratic constraints (IQC). This work puts a particular focus on handling systems with a single integrator. This framework is elaborated in different specific directions as motivated by practical realizations of NCSs, as well as through numerical examples. A novel proof of the discrete time multivariate circle criterion and the Tsypkin criterion for systems including a single integrator is presented, as well as a stability criterion for linear systems with a single integrator subject to variable sampling periods and sector-bounded nonlinear feedback. Four stability criteria for different classes of systems subject to packet loss and time-varying delay are given. Stability criteria for a closed loop system switching between a set of linear time-invariant systems (LTIs) are proved. This result is applied to a single-link NCS with feedback subject to packet loss. Finally, necessary and sufficient conditions for delay-independent stability of an LTI system subject to nonlinear feedback are derived.

Les travaux de cette thèse portent sur l’analyse de stabilité et la synthèse de commandes robustes pour les systèmes affines à commutation en temps continu en présence d’incertitudes paramétriques constantes. On propose deux méthodes de commande permettant de garantir la stabilité asymptotique globale des systèmes affines à commutation avec paramètres inconnus. La première approche est basée sur l’estimation des paramètres inconnus et la reconstruction de l’état d’équilibre associée pour permettre d’appliquer une commande robuste adaptative. La seconde méthode est basée sur une augmentation d’état par l’ajout d’une action intégrale dans la boucle de commande qui garantit une erreur statique nulle. Pour chaque approche, deux lois de commande sont proposées. Une méthode du type « min switching » qui sélectionne la commutation la plus apte à stabiliser le système et une méthode de type « Embedded » permettant de générer une commande polytopique des différents modes possibles. Les résultats sont appliqués aux convertisseurs de puissance de topologie Flyback avec preuve de stabilité dans les deux modes de conduction (continue et discontinue) / This PhD thesis is focused on stability analysis and robust control synthesis for continuous time switching affine systems in presence of constant parametric uncertainties. Two control methods are proposed to guarantee global asymptotic stability of switching affine systems with unknown parameters. The first approach is based on the estimation of the unknown parameters and the reconstruction of the related equilibrium state to allow the application of a robust adaptive control. The second method is based on a state augmentation by adding an integral action in the control loop that guarantees a null steady state error. For each approach, two control laws are proposed. A "min switching" method that selects the most suitable mode to stabilize the system and an "Embedded" method that generates a polytopic control of the different possible modes. The results are applied to Flyback topology power converters with proof of stability in both conduction modes (continuous and discontinuous)

by Kit-man Chan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 82-86). / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Overview of Integrated Service Digital Networks --- p.1 / Chapter 1.2 --- Multirate Loss Networks --- p.5 / Chapter 1.3 --- Previous Work --- p.7 / Chapter 1.4 --- Organization --- p.11 / Chapter 1.5 --- Publications --- p.12 / Chapter 2 --- Call Admission in Multirate Loss Networks --- p.13 / Chapter 2.1 --- Introduction --- p.13 / Chapter 2.2 --- Two Adaptive Routing Rules --- p.15 / Chapter 2.3 --- Call Admission Policies --- p.17 / Chapter 2.4 --- Analysis of Call Admission Policies --- p.25 / Chapter 2.4.1 --- "The CS, LO, GB and the EB Policies" --- p.25 / Chapter 2.4.2 --- The DP Policy --- p.29 / Chapter 2.5 --- Performance Comparisons --- p.32 / Chapter 2.6 --- Concluding Remarks --- p.35 / Chapter 3 --- Least Congestion Routing in Multirate Loss Networks --- p.41 / Chapter 3.1 --- Introduction --- p.41 / Chapter 3.2 --- The M2 and MTB Routings --- p.42 / Chapter 3.2.1 --- M2 Routing --- p.43 / Chapter 3.2.2 --- MTB Routing --- p.43 / Chapter 3.3 --- Bandwidth Sharing Policies and State Aggregation --- p.45 / Chapter 3.4 --- Analysis of M2 Routing --- p.47 / Chapter 3.5 --- Analysis of MTB Routing --- p.50 / Chapter 3.6 --- Numerical Results and Discussions --- p.53 / Chapter 3.7 --- Concluding Remarks --- p.56 / Chapter 4 --- The Least Congestion Routing in WDM Lightwave Networks --- p.60 / Chapter 4.1 --- Introduction --- p.60 / Chapter 4.2 --- Architecture and Some Design Issues --- p.62 / Chapter 4.3 --- The Routing Rule --- p.66 / Chapter 4.4 --- Analysis of the LC Routing Rule --- p.67 / Chapter 4.4.1 --- Fixed Point Model --- p.67 / Chapter 4.4.2 --- Without Direct-link Priority --- p.68 / Chapter 4.4.3 --- With Direct-link Priority --- p.72 / Chapter 4.5 --- Performance Comparisons --- p.73 / Chapter 4.6 --- Concluding Remarks --- p.75 / Chapter 5 --- Conclusions and Future Work --- p.79 / Chapter 5.1 --- Future Work --- p.80

by Kwok Siu Yu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 48-49). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background of switching networks --- p.1 / Chapter 1.2 --- Nonblocking properties of 3-stage networks --- p.5 / Chapter 1.3 --- Wide-sense nonblocking networks --- p.10 / Chapter 1.4 --- Routing algorithms by packing --- p.12 / Chapter 2 --- The Concept of the Upper Ideals --- p.15 / Chapter 3 --- "Routing algorithm over the network [6x10, 3x3, 10x6]" --- p.26 / Chapter 4 --- Simulation Program (SP) --- p.30 / Chapter 5 --- "Nonexistence of routing algorithm over the network [5x8, 3x3, 8x5]" --- p.35 / Chapter 6 --- Packing algorithms --- p.42 / Chapter 7 --- Summary and directions of further study --- p.47