1,720,953 research outputs found
Routing and Disaster Awareness in Optical Networks
No full textOptical networks facilitate the configurations of high-speed network connections with tremendous bandwidth between the optical switches. Optical switches are interconnected by optical fibers that act as the mediums in which data are transferred using lightpaths. Due to the importance of optical networks to many societal needs, e.g., the Internet and banking services, network connections must be configured as efficient and reliable as possible. This thesis focus on two important research topics related to the management and survivability of network connections, namely routing and disaster awareness. Routing enables the assignment of the optimal end-to-end path to each network connection, while disaster awareness increases the preparedness of network operators in ensuring that network connections are protected against the adverse impacts of disasters. The first part of the thesis, namely Chapters 2, 3 and 4 relate to the topic of routing, specifically on technology-aware routing, impairment-aware routing and risk-averse routing. Technology-aware routing is required for establishing network connections across multi-domain networks with technology incompatibilities, impairment-aware routing enables network operators to establish network connections in the presence of transmission impairments, and risk-averse routing enables connections to be assigned with the safest paths (against failing due to disasters). The second part of the thesis, namely Chapters 4 and 5 relate to the topic of disaster awareness, by proposing approaches for ensuring the survivability of network connections in the risk of disasters, such as modeling of (spatiotemporal) disasters, identifying vulnerable connections, detecting spatially-close fiber segments, computing spatially-close intervals of spatially close fibers, and grouping spatially-close fibers efficiently. Though the thesis emphasizes on optical network use cases, the provided insights and contributions in each chapter are general enough to be extended for application in other network types as well.Network Architectures and Service
On Centrality-Related Disaster Vulnerability of Network Regions
No full textNetworks are typically embedded in non-homogeneous areas and different parts/regions of the network may therefore be at risk from different types of disasters. This non-homogeneity leads to difficulties in protecting the network against (the risk of) disasters. Network operators need to be able to integrate predictions on possible future disaster events in the planning of their network operation. Especially the (future) availability of network links is crucial in configuring network connections, since the requested availability of network connections is stipulated in Service Level Agreements and must be satisfied, even under the threat of disasters. In this paper, we propose (1) a novel model to characterize disaster areas, with occurrences of each type of disaster represented by a temporal distribution (e.g., Poisson process), and (2) two metrics, namely a betweenness-centrality metric for network regions and an impact metric that indicates the magnitude of the threat posed by disasters within a network region during a given time period.Embedded System
Spatiotemporal Risk-Averse Routing
No full textA cyber-physical system is often designed as a network in which critical information is transmitted. However, network links may fail, possibly as the result of a disaster. Disasters tend to display spatiotemporal characteristics, and consequently link availabilities may vary in time. Yet, the requested connection availability of traffic must be satisfied at all times, even under disasters. In this paper, we argue that often the spatiotemporal impact of disasters can be predicted, such that suitable actions can be taken, before the disaster manifests, to ensure the availability of connections. Our main contributions are three-fold: (1) we propose a generic grid-based model to represent the risk profile of a network area and relate the risk profile to the availability of links and connections, (2) we propose a polynomial-time algorithm to identify connections that are vulnerable to an emerging disaster risk, and (3) we consider the predicted spatiotemporal disaster impact, and propose a polynomial-time algorithm based on an auxiliary graph to find the most risk-averse path under a time constraint.Network Architectures and Service
Detection of Spatially-Close Fiber Segments in Optical Networks
No full textSpatially-close network fibers have a significant chance of failing simultaneously in the event of man-made or natural disasters within their geographic area. Network operators are interested in the proper detection and grouping of any existing spatially-close fiber segments, to avoid service disruptions due to simultaneous fiber failures. Moreover, spatially-close fibers can further be differentiated by computing the intervals over which they are spatially close. In this paper, we propose (1) polynomial-time algorithms for detecting all the spatially-close fiber segments of different fibers, (2) a polynomial-time algorithm for finding the spatially-close intervals of a fiber to a set of other fibers, and (3) a fast exact algorithm for grouping spatially-close fibers using the minimum number of distinct risk groups. All of our algorithms have a fast running time when simulated on three real-world network topologies.Network Architectures and Service
Backup rules in Software-Defined Networks
No full textThe past century of telecommunications has shown that failures in networks are prevalent. Failure recovery processes are therefore needed. Failure recovery is mainly influenced by (1) detection of the failure, and (2) circumvention of the detected failure. However, especially in SDNs where controllers recompute network state reactively, this leads to high delays. Hence, next to primary rules, backup rules should be installed in the switches to quickly detour traffic once a failure occurs. In this work, we propose algorithms for computing an all-to-all primary and backup network forwarding configuration that is capable of circumventing link and node failures. After initial recovery, we recompute network configuration to guarantee protection from future failures. Our algorithms use packet-labeling to guarantee correct and shortest detour forwarding and are able to discriminate between link and node failures. The computational complexity of our solution is comparable to that of all-to-all shortest paths computations. Our experimental evaluation shows that network configuration complexity decreases significantly compared to classic disjoint paths computations. Finally, we provide a proof-of-concept OpenFlow controller in which our proposed configuration is implemented, demonstrating that it readily can be applied in production networks.Network Architectures and Service
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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