Universität Stuttgart
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Item Open Access Novel network architecture for optical burst transport(2006) Gauger, Christoph; Kühn, Paul (Prof. Dr.-Ing. Dr. h. c. mult.)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. While for years progress 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 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. The method of event-driven simulation is used to evaluate OBTN regarding its node and network resource requirements and QoS performance. Chapter 2 introduces the general characteristics, requirements, and trends for next generation transport networks in general and optical networks in particular. 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 as well as hybrid optical network architectures. Chapter 3 discusses the state of research and technology for optical burst switching. It presents the requirements for key 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. This is supported by Appendix A which analyzes the performance of nodes with fiber delay line buffers. Finally, architectures and realization aspects for burst-switched core nodes are presented to explain their resource and scalability constraints. Chapter 4 motivates and introduces the fundamental concepts of OBTN, 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. Finally, OBTN is compared qualitatively with optical burst switching and hybrid optical networks. Chapter 5 describes a unified resource model which allows dimensioning and evaluating burst-switched architectures with different virtual topologies. Then, it addresses the simulation methodology, the reference evaluation scenario used in Chapter 6 as well as the metrics for node and network resources and QoS performance. Chapter 6 evaluates OBTN and compares it with the two burst-switched reference architectures OBS and Burst-over-Circuit-Switching (BoCS). OBS uses a sparse virtual topology while BoCS employs a full-mesh virtual topology. The evaluations show that for the same high target QoS, suitable OBTN dimensionings require substantially less resources in burst-switched 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. Concluding, OBTN is shown to offer an overall high QoS, to effectively reduce the node resources of the burst-switched client layer, and to perform well in a wavelength-switched network context.Item Open Access Modellierung und Bewertung von Verfahren zur Last- und Leistungsregelung in Steuereinheiten von B-ISDN/ATM-Vermittlungssystemen(2002) Schwarz, Albrecht; Kühn, Paul J. (Prof. Dr.-Ing. Dr. h.c. mult.)Behandelt wird die Problematik der Last- und Leistungsregelung im Kontext der ATM-basierten Breitband-Vermittlungstechnik.Item Open Access On the trade-off between element availability and cost in virtualized network infrastructures(2017) Herker, Sandra; Kirstädter, Andreas (Prof. Dr.-Ing.)Item Open Access Entwurf und Bewertung von Verfahren zur Verkehrslenkung in WDM-Netzen(2002) Späth, Jan; Kühn, Paul J. (Prof. Dr.-Ing. Dr. h. c. mult.)Es werden Verfahren zur Wegesuche und Ressourcen-Belegung in Netzen mit WDM-Technik (WDM: Wavelength Division Multiplex, Wellenlängenmultiplex) entworfen und bewertet.Item Open Access Adaptive error control for stratospheric long-distance optical links(2024) Parthasarathy, Swaminathan; Kirstädter, Andreas (Prof. Dr.-Ing.)Free-space optical (FSO) communication plays a crucial role in aerospace technology, utilizing lasers to establish high-speed, wireless connections over long distances. FSO surpasses conventional RF wireless technology in various aspects and supports high-data-rate connectivity for services such as Internet access, data transfer, voice communication, and image transfer. High-Altitude Platforms (HAPs) have emerged as ideal hosts for FSO communication networks, offering ultra-high data rates for applications like high-speed Internet, video conferencing, telemedicine, smart cities, and autonomous driving. FSO via HAPs ensures minimal latency, making it suitable for real-time tasks like remote surgery and autonomous vehicle control. The swift, long-distance communication links with low delays make FSO-equipped HAPs ideal for RF-congested areas, providing cost-effective solutions in remote regions and contributing to environmental monitoring. This thesis explores the use of adaptive code-rate Hybrid Automatic Repeat Request (HARQ) methods and channel state information (CSI) to improve the transmission efficiency of Free-Space Optical (FSO) links between High Altitude Platforms (HAPs). The study looks at channel problems like atmospheric turbulence and static pointing errors, focusing on the weak fluctuation regime of atmospheric turbulence. It explores the reciprocal behavior in bidirectional FSO channels to improve performance efficiency, providing evidence of channel reciprocity. The research proposes using HARQ, an adaptive Reed-Solomon (RS) code-rate technique, and different CSI types to address these impairments. Simulations of various situations are used to test how well these methods work. This helps us learn more about how efficient HARQ protocols are in inter-HAP FSO links, how important different CSI is in adaptive rate HARQ, and possible ways to make the system more efficient. This thesis looks at the channel model for inter-High Altitude Platform (HAP) Free-Space Optical (FSO) links in great detail, taking atmospheric conditions and static pointing errors into account. The channel is modeled as a lognormal fading channel under a weak fluctuation regime. The principle of channel reciprocity and the measures used to quantify it are discussed, providing a foundational understanding for the subsequent investigations. Forward Error Correction (FEC) schemes, with a specific emphasis on the Reed-Solomon (RS) scheme, and various Automatic Repeat reQuest (ARQ) schemes are thoroughly examined. A meticulous comparison of different ARQ schemes highlights that Selective Repeat ARQ (SR-ARQ) is the most efficient for high-error-rate channels, making it the preferred choice for inter-HAP FSO channels. Conversely, Stop and Wait ARQ (SW-ARQ) and Go-Back-N ARQ (GBN-ARQ) are found to be less suitable for these channels. An innovative approach is introduced, leveraging various types of Channel State Information (CSI) to adjust the Reed-Solomon Forward Error Correction (FEC) code-rate. Four types of CSI: perfect CSI (P-CSI), reciprocal CSI (R-CSI), delayed CSI (D-CSI), and fixed mean CSI (F-CSI) are employed. The adaptation of the Reed-Solomon FEC code-rate, aligned with Selective Repeat ARQ, is explored, and the optimal power selection is identified through rigorous analysis. It shows simulation models that use OMNET++ and gives information about the inter-HAP channel and the event-based selective repeat HARQ model. The study demonstrates reciprocity in the longest recorded ground-to-ground bidirectional Free-Space Optical (FSO) link, holding promise to mitigate signal scintillation caused by atmospheric turbulence. It evaluates the performance of different ARQ protocols and adaptive Hybrid Automatic Repeat Request (HARQ) schemes in inter-HAP FSO communication systems. The results show how channel state information, turbulence in the atmosphere, and pointing errors affect the performance of the system. They also suggest ways to improve system efficiency, such as using CSI prediction and soft combining. These findings offer valuable insights for the design and optimization of ARQ and HARQ schemes in inter-HAP FSO communication systems and suggest promising avenues for future research.Item Open Access Mobility support in industrial edge computing for latency critical applications(2024) Govindaraj, Keerthana; Kirstädter, Andreas (Prof. Dr.-Ing.)During the last decade, Industry 4.0 has gained increasing attention. Mainly two factors drive this enormous growth, firstly the pressing need for novel use cases in manufacturing industries and secondly the rapid progress of aiding technologies in wireless communication. The most prominent use cases that shape the future of manufacturing involve batch-size-one production, predictive maintenance, and AI-based quality monitoring. The devices and applications that majorly constitute these use cases are Augmented Reality devices (AR), Autonomous Guided Vehicle (AGV), and Collaborative Robots (CR). These applications have stringent requirements in terms of the amount of data that needs to be processed and the duration within which it needs to be processed. The devices running these applications are mobile in nature. Therefore, they have a small form factor and are resource constrained. Thus, these applications can be offloaded to computers with high resource availability. Cloud Computing (CC) has already paved its way into manufacturing to resolve some of the resource and accessibility issues. However, it is not a viable solution for Industry 4.0 applications due to the latency requirements as well as security concerns. Edge Computing (EC) is a novel paradigm proposed to alleviate the latency-related issues in many commercial use cases. Thus, EC is explored in this work for its viability in Industry 4.0 use cases to identify the challenges and examine their practicality in manufacturing infrastructure. In EC, the computing entities called Edge Servers (ES) are advised to be placed as close as possible to the source of data generation to reduce the latencies involved in communication. Since the backend network infrastructure in factories has limited capacity, and also over-provisioning it is expensive, the placement of ESs centrally at the factory data center creates an extensive load on the network. Therefore, a distributed EC is necessary ideally at the first hop of the communication channel. The first hop is catered by wireless technologies with high data transmission rates, such as 5G. However, the devices considered in Industry 4.0 use cases are highly mobile and the corresponding applications offloaded are stateful. Thus, to avoid data traffic over the backend network, the application on the ES needs to be migrated to a suitable ES closer to the mobile client. The downtime experienced during the migration process influences the quality of experience of the clients. Additionally, depending on the number of mobile devices present in the system, the number of migration triggers increases. Accordingly, a new ES needs to be selected for all the clients that experience response time violation. Moreover, the migration triggers need to be orchestrated to avoid congesting the backend network with the migration data. The state-of-the-art does not offer a complete mobility support solution for Industry 4.0 scenario. Thus, this work makes two major contributions to provide a practical approach for mobility support in industrial edge computing for latency critical applications. Firstly, it proposes a novel stateful migration scheme that reduces the downtime during the migration by a factor of 4−7 compared to an established state-of-the-art migration scheme. Subsequently, an extension of this migration schemed to further reduce the downtime to "zero". Secondly, it proposes a scheduling scheme to orchestrate multiple simultaneous migration triggers, that in turn reduces the total amount of data migrated by 64.15%. All the statements are backed by thorough evaluations done using an NS3-simulation environment.