Quality of service in optical burst switching networks

Tese dout., Engenharia Electrónica e Computação, Universidade do Algarve, 2009Fundação para e Ciência e a Tecnologi

Offset time-emulated architecture for optical burst switching-modelling and performance evaluation

L'evolució de les xarxes publiques de transport de dades destaca per el continu augment de la demanda de tràfic a la que estan sotmeses. La causa és la imparable popularització d'Internet i del seu ús per a tot tipus d'aplicacions. Les xarxes de commutació de ràfegues òptiques (OBS: Optical Bursts Switching) són una solució extraordinàriament prometedora per la pròxima generació de xarxes, tant per la flexibilitat que ofereixen com per el seu alt rendiment fruit de l'explotació de la multiplexació estadística en el domini òptic.Aquesta tesi presenta l'anàlisi, modelització i avaluació de les xarxes de commutació de ràfegues òptiques basades en l'emulació del temps de compensació (emulated offset time: E-OBS). El concepte d'E-OBS defineix una arquitectura de xarxa OBS per al transportar i commutar ràfegues òptiques en una xarxa troncal en la que, al contrari de l'arquitectura convencional (C-OBS) en la que el temps de compensació s'introdueix des dels nodes d'accés, el temps de compensació s'introdueix en cadascun dels nodes de la xarxa per mitjà d'un retardador de fibra addicional. L'arquitectura E-OBS permet superar algunes de les desavantatges inherents a arquitectures C-OBS, però la seva gran virtut és la compatibilitat amb les xarxes de commutació de circuits òptics (OCS: Optical Circuit Switching) actuals i les futures xarxes de commutació de paquets òptics (OPS: Optical Packet Switching), de manera que les xarxes OBS basades en una arquitectura E-OBS) poden facilitat enormement la transició de unes a les altres.A ala vista dels principals requeriments de disseny de les xarxes OBS, que són la resolució de contencions en el domini òptic, la provisió de qualitat de servei (QoS) i l'òptim encaminament de les ràfegues per tal de minimitzar la congestió de la xarxa, . en aquesta tesi es proposa un disseny de l'arquitectura E-OBS basada en (i) un mètode viable per a la provisió del temps de compensació, (ii) una qualitat alta global de servei, i (iii) un mecanisme d'encaminament que minimitzi congestió de xarxa.- La primera part d'aquesta tesi proporciona la informació documental necessària per al disseny d'E-OBS.- La segona part se centra en l'estudi de la funcionalitat i viabilitat de l'arquitectura E-OBS. S'introdueixen els principis d'operació d'E-OBS i s'identifiquen els principals esculls que presenten les arquitectures C-OBS i que deixen de ser-ho en una arquitectura E-OBS. Alguns d'aquests esculls són la dificultat d'utilitzar un algorisme d'encaminament amb rutes alternatives, la complexitat dels algoritmes de reserva de recursos i la seva falta d'equitat, la complexitat en la provisió de la QoS, etc. En aquesta segona part es constata que l'arquitectura E-OBS redueix la complexitat dels de reserva de recursos i es verifica la viabilitat d'operació i de funcionament de la provisió del tremps de compensació en aquesta arquitectura a partir de figures de comportament obtingudes amb retardadors de fibra comercialment disponibles.- La tercera part encara el problema de la provisió de la QoS. Primer s'hi revisen els conceptes bàsics de QoS així com els mecanismes de tractament de la QoS per a xarxes OBS fent-ne una comparació qualitativa i de rendiment de tots ells. Com a resultat s'obté que el mecanisme que presenta un millor comportament és el d'avortament de la transmissió de les ràfegues de més baixa prioritat quan aquestes col·lisionen amb una de prioritat més alta (es l'anomenat Burst Preemption mechanism), el qual en alguns casos presenta un problema de senyalització innecessària. Aquesta tercera part es conclou amb la proposta d'un mecanisme de finestra a afegir al esquema de Burst Preemption que només funciona sobre una arquitectura E-OBS i que soluciona aquest problema.- En la quarta part s'afronta el problema de l'encaminament en xarxes OBS. S'estudia el comportament dels algoritmes d'encaminament adaptatius, els aïllats amb rutes alternatives i els multicamí distribuïts, sobre xarxes E-OBS. A la vista dels resultats no massa satisfactoris que s'obtenen, es planteja una solució alternativa que es basa en model d'optimització no lineal. Es formulen i resolen dos models d'optimització per als algoritmes encaminament de font multicamí que redueixen notablement la congestió en les xarxes OBS.Finalment, aquesta tesi conclou que l'arquitectura E-OBS és factible, que és més eficient que la C-OBS, que proveeix eficaçment QoS, i que és capaç d'operar amb diverses estratègies d'encaminament i de reduir eficaçment la congestió de xarxa.The fact that the Internet is a packet-based connection-less network is the main driver to develop a data-centric transport network. In this context, the optical burst switching (OBS) technology is considered as a promising solution for reducing the gap between transmission and switching speeds in future networks.This thesis presents the analysis, modelling, and evaluation of the OBS network with Emulated offset-time provisioning (E-OBS). E-OBS defines an OBS network architecture to transport and switch optical data bursts in a core network. On the contrary to a conventional offset-time provisioning OBS (C-OBS) architecture, where a transmission offset time is introduced in the edge node, in an E-OBS network the offset time is provided in the core node by means of an additional fibre delay element. The architecture is motivated by several drawbacks inherent to C-OBS architectures. It should be pointed out that the E-OBS has not been studied intensively in the literature and this concept has been considered rather occasionally.Due to the limitations in optical processing and queuing, OBS networks need a special treatment so that they could solve problems typical of data-centric networks. Contention resolution in optical domain together with quality of service (QoS) provisioning for quality demanding services are, among other things, the main designing issues when developing OBS networks. Another important aspect is routing problem, which concerns effective balancing of traffic load so that to reduce burst congestion at overloaded links. Accounting for these requirements, the design objectives for the E-OBS architecture are (i) feasibility of offset-time provisioning, (ii) an overall high quality of service, and (iii) reduction of network congestion. These objectives are achieved by combining selected concepts and strategies, together with appropriate system design as well as network traffic engineering.The contributions in this thesis can be summarized as follows.- At the beginning, we introduce the principles of E-OBS operation and we demonstrate that C-OBS possesses many drawbacks that can be easily avoided in E-OBS. Some of the discussed issues are the problem of unfairness in resources reservation, difficulty with alternative routing, complexity of resources reservation algorithms, efficiency of burst scheduling, and complexity in QoS provisioning. The feasibility of E-OBS operation is investigated as well; in this context, the impact of congestion in control plane on OBS operation is studied. As a result, we confirm the feasibility of E-OBS operation with commercially available fibre delay elements.- Then, we provide both qualitative and quantitative comparison of the selected, most addressed in the literature, QoS mechanisms. As an outcome a burst preemption mechanism, which is characterized by the highest overall performance, is qualified for operating in E-OBS. Since the preemptive mechanism may produce the overbooking of resources in an OBS network we address this issue as well. We propose the preemption window mechanism to solve the problem. An analytical model of the mechanism legitimates correctness of our solution.- Finally, we concern with a routing problem - our routing objective is to help the contention resolution algorithms in the reduction of burst losses. We propose and evaluate two isolated alternative routing algorithms designed for labelled E-OBS networks. Then we study multi-path source routing and we use network optimization theory to improve it. The presented formulae for partial derivatives, to be used in a non-linear optimization problem, are straightforward and very fast to compute. It makes the proposed non-linear optimization method a viable alternative for linear programming formulations based on piecewise linear approximations.Concluding, E-OBS is shown to be a feasible OBS network architecture of profitable functionality, to support efficiently the QoS provisioning, and to be able to operate with different routing strategies and effectively reduce the network congestion

Algorithms for quality of service provisioning and enhancement in optical burst switched networks

Ph.DDOCTOR OF PHILOSOPH

Artificial intelligence (AI) methods in optical networks: A comprehensive survey

Producción CientíficaArtificial intelligence (AI) is an extensive scientific discipline which enables computer systems to solve problems by emulating complex biological processes such as learning, reasoning and self-correction. This paper presents a comprehensive review of the application of AI techniques for improving performance of optical communication systems and networks. The use of AI-based techniques is first studied in applications related to optical transmission, ranging from the characterization and operation of network components to performance monitoring, mitigation of nonlinearities, and quality of transmission estimation. Then, applications related to optical network control and management are also reviewed, including topics like optical network planning and operation in both transport and access networks. Finally, the paper also presents a summary of opportunities and challenges in optical networking where AI is expected to play a key role in the near future.Ministerio de Economía, Industria y Competitividad (Project EC2014-53071-C3-2-P, TEC2015-71932-REDT

Towards Scalable Design of Future Wireless Networks

Wireless operators face an ever-growing challenge to meet the throughput and processing requirements of billions of devices that are getting connected. In current wireless networks, such as LTE and WiFi, these requirements are addressed by provisioning more resources: spectrum, transmitters, and baseband processors. However, this simple add-on approach to scale system performance is expensive and often results in resource underutilization. What are, then, the ways to efficiently scale the throughput and operational efficiency of these wireless networks? To answer this question, this thesis explores several potential designs: utilizing unlicensed spectrum to augment the bandwidth of a licensed network; coordinating transmitters to increase system throughput; and finally, centralizing wireless processing to reduce computing costs. First, we propose a solution that allows LTE, a licensed wireless standard, to co-exist with WiFi in the unlicensed spectrum. The proposed solution bridges the incompatibility between the fixed access of LTE, and the random access of WiFi, through channel reservation. It achieves a fair LTE-WiFi co-existence despite the transmission gaps and unequal frame durations. Second, we consider a system where different MIMO transmitters coordinate to transmit data of multiple users. We present an adaptive design of the channel feedback protocol that mitigates interference resulting from the imperfect channel information. Finally, we consider a Cloud-RAN architecture where a datacenter or a cloud resource processes wireless frames. We introduce a tree-based design for real-time transport of baseband samples and provide its end-to-end schedulability and capacity analysis. We also present a processing framework that combines real-time scheduling with fine-grained parallelism. The framework reduces processing times by migrating parallelizable tasks to idle compute resources, and thus, decreases the processing deadline-misses at no additional cost. We implement and evaluate the above solutions using software-radio platforms and off-the-shelf radios, and confirm their applicability in real-world settings.PhDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133358/1/gkchai_1.pd

Datacenter Traffic Control: Understanding Techniques and Trade-offs

Datacenters provide cost-effective and flexible access to scalable compute and storage resources necessary for today's cloud computing needs. A typical datacenter is made up of thousands of servers connected with a large network and usually managed by one operator. To provide quality access to the variety of applications and services hosted on datacenters and maximize performance, it deems necessary to use datacenter networks effectively and efficiently. Datacenter traffic is often a mix of several classes with different priorities and requirements. This includes user-generated interactive traffic, traffic with deadlines, and long-running traffic. To this end, custom transport protocols and traffic management techniques have been developed to improve datacenter network performance. In this tutorial paper, we review the general architecture of datacenter networks, various topologies proposed for them, their traffic properties, general traffic control challenges in datacenters and general traffic control objectives. The purpose of this paper is to bring out the important characteristics of traffic control in datacenters and not to survey all existing solutions (as it is virtually impossible due to massive body of existing research). We hope to provide readers with a wide range of options and factors while considering a variety of traffic control mechanisms. We discuss various characteristics of datacenter traffic control including management schemes, transmission control, traffic shaping, prioritization, load balancing, multipathing, and traffic scheduling. Next, we point to several open challenges as well as new and interesting networking paradigms. At the end of this paper, we briefly review inter-datacenter networks that connect geographically dispersed datacenters which have been receiving increasing attention recently and pose interesting and novel research problems.Comment: Accepted for Publication in IEEE Communications Surveys and Tutorial