Transport networks form the backbone of communication networks by cost-efficiently offering huge bandwidth and by guaranteeing a high service quality and availability. These requirements can best be met by using optical communication technologies. Currently, wavelength-switching is the most prominent network technology employing optical fiber communication and wavelength division multiplexing. It transports data in circuit-switched wavelength channels, the so-called lightpaths. While for years

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... rogress in optical networks has been defined by ever increasing transmission bit-rates, higher flexibility and manageability as well as multi-service and multi-layer integration are equally important criteria today. Accounting for these trends, optical burst switching (OBS) has been proposed as a highly dynamic optical network architecture. It offers fine-granular transport of different packet-switched services and applies statistical multiplexing directly in the optical layer. This thesis presents the design, modeling, and evaluation of the optical burst transport network architecture (OBTN). The architecture is motivated by the need for flexible, scalable, and cost-efficient transport in next generation networks. In addition, it is stimulated by the research activities towards highly dynamic optical network infrastructures. OBTN defines a network architecture to transport and switch optical burst data in a core network. The design objectives for the OBTN architecture are (i) an overall high quality of service, (ii) a network design allowing for cost-efficiency and scalability, and (iii) a network evolution perspective based on the current wavelength-switched networks. These objectives are achieved by combining selected concepts, architectures, and strategies of optical burst and optical packet switching as well as of multi-layer traffic engineering. In order to provide the background information for the design of OBTN, Chapter 2 introduces the general characteristics, requirements, and trends for next generation transport networks. Also, it discusses the concept of layering in next generation networks and its application in layer networks for the virtualization of transport resources. Consequently, virtual topology design and dimensioning are analyzed to quantify the trade-offs regarding connectivity and resource requirements. Chapter 2 also reviews the fundamental technologies as well as currently emerging data and control plane architectures for optical transport networks. This presentation is then extended towards a long-term perspective. It describes architectural constraints and classification criteria for highly dynamic optical network architectures. These criteria are used to characterize the fast optical circuit switching, optical burst switching, and optical packet switching architectures. Then, hybrid optical network architectures are discussed as a framework to combine wavelength-switched and optical burst/packet-switched networks. i ii Summary Chapter 3 discusses the state of research and technology for optical burst switching to structure the design space and identify promising approaches. Thus, it presents the requirements for the different functions in an OBS network and classifies the proposed architectures and mechanisms. Particularly, it addresses contention resolution which is necessary to achieve a high QoS in burst-switched networks. Here, wavelength conversion, fiber delay line buffering, alternative/deflection routing, and their combinations are looked at. It is concluded that wavelength conversion is a promising primary contention resolution strategy but should be complemented by FDL buffering and/or alternative routing. Thus, architectures, parameters, and operational strategies for FDL buffers are discussed in detail. This is supported by Appendix A which analyzes the performance of shared FDL buffers for different configurations and traffic characteristics. The review of alternative/deflection routing shows that it can only support other contention resolution schemes if it is closely controlled, i.e., if extensive deflections and route variations are avoided. Finally, architectures and realization aspects for burst-switched core nodes are presented to understand their resource and scalability constraints. Chapter 4 presents the design rationale for OBTN and explains how OBTN combines a burstswitched client layer network with a wavelength-switched server layer network. Then, it introduces its fundamental concepts, namely the dense virtual topology, constrained alternative routing, and shared overflow capacity. These components are analyzed regarding their consequences for the overall node and network architecture. Further architectural details and variants as well as operational strategies of OBTN are discussed to complete the presentation. Finally, a qualitative discussion of OBTN with respect to optical burst switching and hybrid optical networks concludes this chapter. Chapter 5 describes a unified resource model which allows to dimension and evaluate burstswitched architectures with different virtual topologies. Also, it details the dimensioning process for OBTN. Then, it addresses the simulation methodology and the reference evaluation scenario used in Chapter 6. It discusses metrics for node and network resources as well as for QoS performance. Finally, it derives QoS objectives for burst-switched core networks. Chapter 6 evaluates OBTN and compares it with the two burst-switched reference architectures OBS and Burst-over-Circuit-Switching. OBS uses a sparse virtual topology while BoCS employs a full-mesh virtual topology. The evaluations in Section 6.1 show that for the same high target QoS, suitable OBTN dimensionings require substantially less resources in burstswitched nodes than OBS and slightly less than BoCS. This improvement comes at the cost of higher resource requirements compared to OBS in the underlying wavelength-switched server layer. However, applying the cost relations for lambda grid networks, in which bandwidth is considered a commodity and client layer resources the major cost driver, OBTN yields an overall cost reduction. The best results for OBTN are obtained when approximately 10 % of the network capacity is assigned as shared overflow capacity. The comparison of OBTN and OBS is extended towards OBS architectures without an FDL buffer and OBS architectures with alternative routing. It is demonstrated that bufferless OBS with and without alternative routing requires approximately the same amount of server layer resources as OBTN. However, it consumes more client layer resources. For OBS with an FDL buffer, alternative routing does neither impact the client layer nor the server layer resources substantially. Furthermore, the effectiveness of constrained alternative routing and of the shared overflow capacity in OBTN is assessed by isolating them. This is achieved by comparing OBTN Zusammenfassung Transportnetze stellen das Rückgrad von Telekommunikationsnetzen dar, für die sie große Bandbreiten kostengünstig, ausfallsicher und mit hoher Dienstgüte bereitstellen. Da diese Anforderungen durch optische Kommunikationsnetze am besten erfüllt werden können, basieren Transportnetze heute meist auf Glasfasernetzen mit Wellenlängenmultiplex-Technik. Die momentan wichtigste optische Netzarchitektur schaltet im Netz Wellenlängenkanäle und baut damit sogenannte Lichtpfade auf. In diesen Lichtpfaden werden die Daten verschiedenster darüber liegender Netzschichten transportiert. Viele Jahre lang wurde Fortschritt in optischen Netzen mit stetig steigenden Übertragungsbitraten gleichgestellt. Inzwischen haben aber hohe Flexibilität und Steuerbarkeit sowie die Möglichkeit verschiedene Transportdienste und Netzschichten auf einer Platform zu integrieren eine ebenso hohe Bedeutung erlangt.