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Y. Nishimura

Bio: Y. Nishimura is an academic researcher from NEC. The author has contributed to research in topics: Spare part & Synchronous optical networking. The author has an hindex of 1, co-authored 1 publications receiving 192 citations.

Papers
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Proceedings ArticleDOI
02 Dec 1990
TL;DR: In order to achieve fast restoration, a distributed control mechanism that is applicable to both line and path restoration is proposed, and the shared use of spare channels for various failure scenarios, including multiple failure cases, are allowed.
Abstract: With the advent of networking technologies intelligent network elements, such as the digital cross-connect system (DCS), will make it possible to dynamically reconfigure a network for restoration purposes. Both restoration control of DCSs and spare-channel design issues are presented, and how they work together so that a fast and economical SONET self-healing network is obtained. In order to achieve fast restoration, a distributed control mechanism that is applicable to both line and path restoration is proposed. The proposed method allows the shared use of spare channels for various failure scenarios, including multiple failure cases, so that the efficient use of spare channels can be achieved. A linear-programming-based scheme is proposed to obtain spare-channel assignment, where a network-flow technique is used. Through a simulation study, a fast and economical self-healing network is verified. >

193 citations


Cited by
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Book
01 Jan 2004
TL;DR: Throughout, the authors focus on the traffic demands encountered in the real world of network design, and their generic approach allows problem formulations and solutions to be applied across the board to virtually any type of backbone communication or computer network.
Abstract: In network design, the gap between theory and practice is woefully broad. This book narrows it, comprehensively and critically examining current network design models and methods. You will learn where mathematical modeling and algorithmic optimization have been under-utilized. At the opposite extreme, you will learn where they tend to fail to contribute to the twin goals of network efficiency and cost-savings. Most of all, you will learn precisely how to tailor theoretical models to make them as useful as possible in practice. Throughout, the authors focus on the traffic demands encountered in the real world of network design. Their generic approach, however, allows problem formulations and solutions to be applied across the board to virtually any type of backbone communication or computer network. For beginners, this book is an excellent introduction. For seasoned professionals, it provides immediate solutions and a strong foundation for further advances in the use of mathematical modeling for network design. (Less)

1,093 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined different approaches to protect a mesh-based WDM optical network from such failures and proposed distributed protocols for path and link restoration, and formulated a model of protection-switching times for different protection schemes based on a fully distributed control network.
Abstract: In a wavelength-division-multiplexing (WDM) optical network, the failure of network elements (e.g., fiber links and cross connects) may cause the failure of several optical channels, thereby leading to large data losses. This study examines different approaches to protect a mesh-based WDM optical network from such failures. These approaches are based on two survivability paradigms: 1) path protection/restoration and 2) link protection/restoration. The study examines the wavelength capacity requirements, and routing and wavelength assignment of primary and backup paths for path and link protection and proposes distributed protocols for path and link restoration. The study also examines the protection-switching time and the restoration time for each of these schemes, and the susceptibility of these schemes to multiple link failures. The numerical results obtained for a representative network topology with random traffic demands demonstrate that there is a tradeoff between the capacity utilization and the susceptibility to multiple link failures. We find that, on one hand, path protection provides significant capacity savings over link protection, and shared protection provides significant savings over dedicated protection; while on the other hand, path protection is more susceptible to multiple link failures than link protection, and shared protection is more susceptible to multiple link failures than dedicated protection. We formulate a model of protection-switching times for the different protection schemes based on a fully distributed control network. We propose distributed control protocols for path and link restoration. Numerical results obtained by simulating these protocols indicate that, for a representative network topology, path restoration has a better restoration efficiency than link restoration, and link restoration has a faster restoration time compared with path restoration.

913 citations

Proceedings ArticleDOI
21 Mar 1999
TL;DR: This study examines different approaches to protect mesh based WDM optical networks from single-link failures, and formulated integer linear programs to determine the capacity requirements for the above protection schemes for a static traffic demand.
Abstract: This investigation considers optical networks which employ wavelength cross-connects that enable the establishment of wavelength-division-multiplexed (WDM) channels, between node-pairs. In such and other networks, the failure of a network element (e.g., fiber link, cross-connect, etc.) may cause the failure of several optical channels, thereby leading to large data losses. This study examines different approaches to protect mesh based WDM optical networks from single-link failures. These approaches are based on two basic survivability paradigms: (a) path protection/restoration, and (b) link protection/restoration. In path- and link-protection schemes, backup paths and wavelengths are reserved in advance at the time of call setup. Path- and link-restoration schemes are dynamic schemes in which backup paths are discovered (from the spare capacity in the network) upon the occurrence of a failure. In part 1 of this study presented in this paper, we formulated integer linear programs to determine the capacity requirements for the above protection schemes for a static traffic demand.

727 citations

Journal ArticleDOI
Bharat T. Doshi1, Subrahmanyam Dravida1, P. Harshavardhana1, Oded Hauser1, Yufei Wang1 
TL;DR: This paper reports test results for large carrier-scale networks that indicate that subsecond restoration, high capacity efficiency, and scalability can be achieved without fault isolation and with moderate processing.
Abstract: The explosion of data traffic and the availability of enormous bandwidth via dense wavelength division multiplexing (DWDM) and optical amplifier (OA) technologies make it important to study optical layer networking and restoration. This paper is concerned with fast distributed restoration and provisioning for generic mesh-based optical networks. We consider two problems of practical importance: determining the best restoration route for each wavelength demand, given the network topology and the capacities and primary routes of all demands, and determining primary and restoration routes for each wavelength demand to minimize network capacity and cost. The approach we propose for both problems is based on precomputing. For each problem, we describe specific algorithms used for computing routes. We also describe endpoint-based failure detection, message flows, and cross-connect actions for execution of fast restorations. Finally, we report test results for large carrier-scale networks that include both the computational performance of the optimization algorithms and the restoration speed obtained by simulation. Our results indicate that subsecond restoration, high capacity efficiency, and scalability can be achieved without fault isolation and with moderate processing. We also discuss methods for scaling algorithms to problems with very large numbers of demands. The wavelength routing and restoration algorithms, the failure detection, and the message exchange and activation architectures we propose are collectively known as WaveStar™ advanced routing platform.

312 citations

Journal ArticleDOI
TL;DR: The main finding is that a span-restorable mesh network can be extremely robust under dual-failure events against which they are not specifically designed.
Abstract: The most common aim in designing a survivable network is to achieve restorability against all single span failures, with a minimal investment in spare capacity. This leaves dual-failure situations as the main factor to consider in quantifying how the availability of services benefit from the investment in restorability. We approach the question in part with a theoretical framework and in part with a series of computational routing trials. The computational part of the analysis includes all details of graph topology, capacity distribution, and the details of the restoration process, effects that were generally subject to significant approximations in prior work. The main finding is that a span-restorable mesh network can be extremely robust under dual-failure events against which they are not specifically designed. In a modular-capacity environment, an adaptive restoration process was found to restore as much as 95% of failed capacity on average over all dual-failure scenarios, even though the network was designed with minimal spare capacity to assure only single-failure restorability. The results also imply that for a priority service class, mesh networks could provide even higher availability than dedicated 1+1 APS. This is because there are almost no dual-failure scenarios for which some partial restoration level is not possible, whereas with 1+1 APS (or rings) there are an assured number of dual-failure scenarios for which the path restorability is zero. Results suggest conservatively that 20% or more of the paths in a mesh network could enjoy this ultra-high availability service by assigning fractional recovery capacity preferentially to those paths upon a dual failure scenario.

269 citations