Efficient resource utilization and fast failure recovery are essential design goals of next-generation backbone networks. The need for efficient resource utilization has motivated the development of various protocols and techniques that offer data services over legacy backbone networks such as Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH). Enabling improved utilization with enhanced network reliability requires various network optimizations, both at the protocol and system levels. In this dissertation, we present a set of network optimization techniques that improve the performance of an end-user connected to classical packet networks such as Internet. First, we introduce an efficient path selection algorithm that enables seamless bandwidth upgrade for an existing Ethernet connection over SONET/SDH backbone using virtual concatenation technique. We also provide a heterogenous concatenation technique that improves the bandwidth utilization and that is easy to maintain. Second, we present a novel failure localization technique, that can detect single-link or simultaneous multiple-link failures. This technique is based on constructing a set of monitoring paths and cycles from one or more monitoring locations in the network. Third, we present an efficient routing and wavelength assignment scheme for backbone networks with stale network-state information. Finally, we present an e±cient server placement scheme for supporting multiple-description-coding (MDC) based media streaming over content delivery networks. We show that by using MDC-encoded media, intelligent server placement, and efficient path selection, the performance of an end-user can be greatly improved.

The rapid increase in demand for bandwidth in optical networks over the last two decades has led to the development of wavelength division multiplexing where multiple channels are transmitted simultaneously at different wavelengths over a single optical-fiber to maximize the usage of the bandwidth available in fiber. Increasing demand for bandwidth has led to narrower channel spacing and the use of advanced modulation schemes that are more spectrally efficient than traditional on-off keying techniques [1]. Nonlinearities and dispersion effects in fiber accumulate over a long distance and can adversely affect the quality of a channel. Hence the ability to measure detailed features of the optical spectrum is crucial to study the performance of a communication link. A conventional optical spectrum analyzer (OSA) based on a diffraction grating has a wide wavelength or frequency scanning range, but suffers from poor frequency resolution. The narrowest resolution bandwidth reported for a grating based OSA is - 0.06nm or 7.5GHz at 1550nm [1]. Various spectral features of interest, such as the transmission spectrum of a laser and modulation spectrum of a channel require sub-picometer resolution, which cannot be achieved by conventional methods using a diffraction grating. High resolution spectrum analyzers (HRSAs) have been built based on heterodyne detection where a portion of the optical spectrum is converted to radio-frequency (RF) with DC corresponding to the local-oscillator (LO) central frequency [3-6]. This is a common technique used in RF-spectrum analyzers. The resolution bandwidth is determined by the electrical bandwidth of the optical receiver. The lowest resolution bandwidth reported is of the order of tens of MHz [6]. Widespread implementation of these instruments however, has been limited owing to their cost and size, one of the major factors being the external cavity (ECT) lasers used as the local-oscillator source in such instruments. We have built a coherent-channel analyzer (CCA) based on balanced coherent detection using a commercial distributed-feedback (DFB) laser as the LO. The use of a DFB laser for the CCA has the potential of reducing the cost of the instrument by at least one-tenth of the price of an HRSA. In this thesis we describe the working of the CCA. We provide an end-to-end system model, analyze the resolution and sensitivity performance of the system, and demonstrate a frequency resolution of 100MHz over the DFB tuning range of 200GHz with a sensitivity of -95dBm. The CCA provides a practical, cost and size effective alternative to the HRSA at the cost of tunability. / Graduate

Optical networks based on Wavelength Division Multiplexing (WDM) technology show many clear benefits in terms of high capacity, flexibility and low power consumption. All these benefits make WDM networks the preferred choice for today’s and future transports solutions which are strongly driven by a plethora of emerging online services. In such a scenario, capability to provide high capacity during the service provisioning phase is of course very important, but it is not the only requirement that plays a central role. Traffic dynamicity is another essential aspect to consider because in many scenarios, e.g., in the case of real time multimedia services, the connections are expected to be provisioned and torn down quickly and relatively frequently. High traffic dynamicity may put a strain on the network control and management operations (i.e., the overhead due to control message exchange can grow rapidly) that coordinate any provisioning mechanisms. Furthermore, survivability, in the presence of new failure scenarios that goes beyond the single failure assumption, is still of the utmost importance to minimize the network disruptions and data losses. In other words, protection against any possible future failure scenario where multiple faults may struck simultaneously, asks for highly reliable provisioning solutions. The above consideration have a general validity i.e., can be equally applied to any network segment and not just limited to the core part. So, we also address the problem of service provisioning in the access paradigm. Long reach Passive Optical Networks (PONs) are gaining popularity due to their cost, reach, and bandwidth advantages in the access region. In PON, the design of an efficient bandwidth sharing mechanism between multiple subscribers in the upstream direction is crucial. In addition, Long Reach PONs (LR-PONs) introduces additional challenges in terms of packet delay and network throughput, due to their extended reach. It becomes apparent that effective solutions to the connection provisioning problem in both the core and access optical networks with respect to the considerations made above can ensure a truly optimal end-to-end connectivity while making an efficient usage of resources. The first part of this thesis focuses on a control and management framework specifically designed for concurrent resource optimization in WDM-based optical networks in a highly dynamic traffic scenario. The framework and the proposed provisioning strategies are specifically designed with the objective of: (i) allowing for a reduction of the blocking probability and the control overhead in a Path Computation Element (PCE)-based network architecture, (ii)  optimizing resource utilization for a traffic scenario that require services with diverse survivability requirements which are achieved by means of  dedicated and shared path-protection, and (iii) designing provisioning mechanism that guarantees high connection availability levels in Double Link Failures (DLF) scenarios. The presented results show that the proposed dynamic provisioning approach can significantly improve the network blocking performance while making an efficient use of primary/backup resources whenever protection is required by the provisioned services. Furthermore, the proposed DLF schemes show good performance in terms of minimizing disruption periods, and allowing for enhanced network robustness when specific services require high connection availability levels. In the second part of this thesis, we propose efficient resource provisioning strategies for LR-PON. The objective is to optimize the bandwidth allocation in LR-PONs, in particular to: (i) identify the performance limitations associated with traditional (short reach) TDM-PON based Dynamic Bandwidth Allocation (DBA) algorithms when employed in long reach scenarios, and (ii) devise efficient DBA algorithms that can mitigate the performance limitations imposed by an extended reach. Our proposed schemes show noticeable performance gains when compared with conventional DBA algorithms for short-reach PON as well as specifically devised approaches for long reach. / <p>QC 20130520</p>

The emergence of new bandwidth-intensive applications articulated by distance learning, online gaming, Web 2.0 and movie delivery by means of high-definition video, has ultimately justified the necessity of upgrading the access network infrastructure to provide fat-bandwidth pipelines at subscriber close proximity. Passive optical networks (PONs) are an emerging technology to deliver these services. This thesis presents innovative work performed towards the application of coarse wavelength division multiplexing (CWDM) to route communications to and from reflective optical network units (ONUs) incorporated in time and wavelength division multiplexed PONs. The concept of coarse and dense WDM grid integration and its adaptation in access networks to map, for the first time, selective closely-spaced wavelengths into coarse passband windows of Gaussian and flat-top arrayed waveguide gratings (AWGs), exhibiting coarse-fine grooming, is initially developed. This is followed by the identification of a new network architecture combining multiple PONs, using a coarse AWG to form a next-generation access network. A significant feature of this approach allows for time division multiplexing (TDM) and WDM PON technologies to be integrated through the 7 nm coarse passband windows of a single AWG, providing for interoperability and high scalability. The network performance through simulation, in the presence of polarisation-dependent wavelength shift and associated polarisation-dependent loss, shows the capability of a single optical line terminal (OLT) to access various physical PONs in 25 km proximity with multiple wavelengths through a single AWG router. This approach enables centralised bandwidth allocation and a smooth migration path between time-shared and densely-penetrated access networks. Furthermore, to demonstrate full-duplex operation, allowing for increased bandwidth utilisation of the reflective access network architecture, full-duplex functionality is achieved by using polarisation division multiplexing. This is implemented in the OLT by assigning each ONU downstream data and continues waves on orthogonal states of polarisation. Hence, by assuming the use of symmetrical broadband services, the novel multi-PON access network verifies its potential to double the bandwidth utilisation for each subscriber, allowing for increased bidirectional network throughput. In addition, an experimental test-bed is performed which demonstrates the core operation of the network being, by means of a readily-available 2.7 nm-wide AWG router. Hence, the practical feasibility of the new access network concept is demonstrated.

Zhao, Qiguang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 72-76). / Abstracts in English and Chinese. / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Telecommunications network hierarchy --- p.2 / Chapter 1.2 --- PON architectures for access networks --- p.4 / Chapter 1.2.1 --- TDM-PON --- p.5 / Chapter 1.2.2 --- WDM-PON --- p.7 / Chapter 1.3 --- Motivation of this thesis --- p.8 / Chapter 1.4 --- Outline of this thesis --- p.11 / Chapter Chapter 2 --- Previous Internetworking Architectures for Optical Network Units in Passive Optical Networks --- p.12 / Chapter 2.1 --- Introduction --- p.13 / Chapter 2.2 --- Previous internetworking architectures with ONU-broadcast capability / Chapter 2.2.1 --- Virtual ring network construction --- p.14 / Chapter 2.2.2 --- Reflection mechanism employing a FBG --- p.15 / Chapter 2.2.3 --- Loop-back mechanism in TDM-PON --- p.16 / Chapter 2.3 --- Previous internetworking architectures with ONU-VPGs formation capability --- p.17 / Chapter 2.3.1 --- E-CDMA application --- p.17 / Chapter 2.3.2 --- SCM technique --- p.18 / Chapter 2.3.3 --- Reflective waveband grouping mechanism --- p.20 / Chapter 2.4 --- Previous protection scheme for internetworking architectures --- p.21 / Chapter 2.4.1 --- Local ring protection in TDM-PON --- p.21 / Chapter 2.5 --- Summary --- p.22 / Chapter Chapter 3 --- Novel Internetworking Architecture with ONU-Broadcast Capability in a WDM-PON --- p.24 / Chapter 3.1 --- Introduction --- p.25 / Chapter 3.2 --- Network topology and wavelength assignment --- p.26 / Chapter 3.3 --- Operation principle --- p.27 / Chapter 3.4 --- Experimental demonstration --- p.31 / Chapter 3.5 --- Power budget and scalability --- p.34 / Chapter 3.6 --- Summary --- p.36 / Chapter Chapter 4 --- Novel Internetworking Architectures with ONU- VPGs Formation Capability in a WDM-PON --- p.37 / Chapter 4.1 --- Introduction --- p.38 / Chapter 4.2 --- Novel architecture with ONU-VPGs formation based on RF tone technique --- p.39 / Chapter 4.2.1 --- Introduction --- p.39 / Chapter 4.2.2 --- Network topology and wavelength assignment --- p.40 / Chapter 4.2.3 --- Media access control protocol: CSMA/CA protocol --- p.42 / Chapter 4.2.4 --- Experimental demonstration --- p.43 / Chapter 4.2.5 --- Discussion --- p.47 / Chapter 4.2.6 --- Summary --- p.49 / Chapter 4.3 --- Novel architecture with ONU-VPGs formation in optical layer --- p.51 / Chapter 4.3.1 --- Introduction --- p.51 / Chapter 4.3.2 --- Network topology and wavelength assignment --- p.51 / Chapter 4.3.3 --- Operation principle --- p.54 / Chapter 4.3.4 --- Experimental demonstration --- p.56 / Chapter 4.3.5 --- Discussion --- p.58 / Chapter 4.3.6 --- Summary --- p.65 / Chapter 4.4 --- Comparisons --- p.66 / Chapter 4.5 --- Summary --- p.67 / Chapter Chapter 5 --- Summary and Future Works --- p.68 / Chapter 5.1 --- Summary of the thesis --- p.69 / Chapter 5.2 --- Future works --- p.70 / LIST OF PUBLICATIONS --- p.71 / BIBLIOGRAPHY --- p.72

Optical signal-to-noise ratio (OSNR) is considered as the dominant performance parameter at the physical layer in optical networks. This thesis is interested in control and optimization of channel OSNR by using optimization and game-theoretic approaches, incorporating two physical constraints: the link capacity constraint and the channel OSNR target. To start, we study OSNR optimization problems with link capacity constraints in single point-to-point fiber links via two approaches. We first present a framework of a Nash game between channels towards optimizing individual channel OSNR. The link capacity constraint is imposed as a penalty term to each cost function. The selfish behavior in a Nash game degrades the system performance and leads to the inefficiency of Nash equilibria. From the system point of view, we formulate a system optimization problem with the objectives of achieving an OSNR target for each channel while satisfying the link capacity constraint. As an alternative to study the efficiency of Nash equilibria, we use the system framework to investigate the effects of parameters in cost functions in the game-theoretic framework. Then extensions to multi-link and mesh topologies are carried out. We propose a partition approach by using the flexibility of channel power adjustment at optical switches. The multi-link structure is partitioned into stages with each stage being a single sink. By fully using the flexibility, a more natural partition approach is applied to mesh topologies where each stage is a single link. The closed loop in mesh topologies can be unfolded by selecting a starting link. Thus instead of maximization of channel OSNR from end to end, we consider minimization of channel OSNR degradation between stages. We formulate a partitioned Nash game which is composed of ladder-nested stage Nash games. Distributed algorithms towards the computation of a Nash equilibrium solution are developed for all different game frameworks. Simulations and experimental implementations provide results to validate the applicability of theoretical results.

We study the stability of power control algorithms applied to optical networks in the presence of both time-delays and uncertainties. The objective of power control algorithms acting on optical networks is to ensure each signal channel attains an optimal optical signal-to-noise ratio (OSNR) value such that transmission errors are minimized. The inputs to the optical network are the transmitter powers and the outputs of the optical network are the OSNR values. The primal control algorithms adjust the channel powers at the transmitters using the channel OSNR values as feedbacks to attain OSNR optimality. We also present the dual control algorithm located at the links which transmits a channel price as an additional feedback to the primal control algorithms. Together, these are called primal-dual control algorithms. We present robust OSNR models for optical networks with multiple time-delays. Specifically, we consider additive system uncertainties, input multiplicative uncertainties on the signal powers, and transmitter noise uncertainties, all within a norm-bounded uncertainty framework. We analyze and modify both central cost based algorithms and game-theoretic based algorithms, with an emphasis on the latter, to ensure the stability of the closed-loop system. We apply time-delay stability analyses to exploit the structures of the closed-loop systems for each type of control algorithm. These techniques include frequency analyses, Lyapunov-Razumikhin techniques, and Lyapunov-Krasovskii techniques. Due to nonlinearities in the closed-loop system models, and their time-scale separated dynamics, we apply singular perturbation theory modified to handle either Lyapunov-Razumikhin theory or Lyapunov-Krasovskii theory. Singular perturbation theory, modified for time-delays, allows us to decouple complicated closed-loop systems into two simpler subsystems, one on a "slow" time-scale, and the other on a "fast" time-scale. We develop stability conditions for primal algorithms applied to arbitrary networks with delays. We also develop stability conditions for primal-dual algorithms applied to single-links, single-sink networks, two channel networks, and multi-link networks with both time-delays and uncertainties. The main results are presented as either LMI conditions and algebraic criteria. Simulations verify the stability of the closed-loop systems in the presence of time-delays. In addition, the simulations show the stabilization of perturbed systems at the expense of transient convergence time.

Optical signal-to-noise ratio (OSNR) is considered as the dominant performance parameter at the physical layer in optical networks. This thesis is interested in control and optimization of channel OSNR by using optimization and game-theoretic approaches, incorporating two physical constraints: the link capacity constraint and the channel OSNR target. To start, we study OSNR optimization problems with link capacity constraints in single point-to-point fiber links via two approaches. We first present a framework of a Nash game between channels towards optimizing individual channel OSNR. The link capacity constraint is imposed as a penalty term to each cost function. The selfish behavior in a Nash game degrades the system performance and leads to the inefficiency of Nash equilibria. From the system point of view, we formulate a system optimization problem with the objectives of achieving an OSNR target for each channel while satisfying the link capacity constraint. As an alternative to study the efficiency of Nash equilibria, we use the system framework to investigate the effects of parameters in cost functions in the game-theoretic framework. Then extensions to multi-link and mesh topologies are carried out. We propose a partition approach by using the flexibility of channel power adjustment at optical switches. The multi-link structure is partitioned into stages with each stage being a single sink. By fully using the flexibility, a more natural partition approach is applied to mesh topologies where each stage is a single link. The closed loop in mesh topologies can be unfolded by selecting a starting link. Thus instead of maximization of channel OSNR from end to end, we consider minimization of channel OSNR degradation between stages. We formulate a partitioned Nash game which is composed of ladder-nested stage Nash games. Distributed algorithms towards the computation of a Nash equilibrium solution are developed for all different game frameworks. Simulations and experimental implementations provide results to validate the applicability of theoretical results.

We study the stability of power control algorithms applied to optical networks in the presence of both time-delays and uncertainties. The objective of power control algorithms acting on optical networks is to ensure each signal channel attains an optimal optical signal-to-noise ratio (OSNR) value such that transmission errors are minimized. The inputs to the optical network are the transmitter powers and the outputs of the optical network are the OSNR values. The primal control algorithms adjust the channel powers at the transmitters using the channel OSNR values as feedbacks to attain OSNR optimality. We also present the dual control algorithm located at the links which transmits a channel price as an additional feedback to the primal control algorithms. Together, these are called primal-dual control algorithms. We present robust OSNR models for optical networks with multiple time-delays. Specifically, we consider additive system uncertainties, input multiplicative uncertainties on the signal powers, and transmitter noise uncertainties, all within a norm-bounded uncertainty framework. We analyze and modify both central cost based algorithms and game-theoretic based algorithms, with an emphasis on the latter, to ensure the stability of the closed-loop system. We apply time-delay stability analyses to exploit the structures of the closed-loop systems for each type of control algorithm. These techniques include frequency analyses, Lyapunov-Razumikhin techniques, and Lyapunov-Krasovskii techniques. Due to nonlinearities in the closed-loop system models, and their time-scale separated dynamics, we apply singular perturbation theory modified to handle either Lyapunov-Razumikhin theory or Lyapunov-Krasovskii theory. Singular perturbation theory, modified for time-delays, allows us to decouple complicated closed-loop systems into two simpler subsystems, one on a "slow" time-scale, and the other on a "fast" time-scale. We develop stability conditions for primal algorithms applied to arbitrary networks with delays. We also develop stability conditions for primal-dual algorithms applied to single-links, single-sink networks, two channel networks, and multi-link networks with both time-delays and uncertainties. The main results are presented as either LMI conditions and algebraic criteria. Simulations verify the stability of the closed-loop systems in the presence of time-delays. In addition, the simulations show the stabilization of perturbed systems at the expense of transient convergence time.

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