1,720,972 research outputs found
On-line routing of MPLS tunnels with time-varying bandwidth profiles
No full textWe consider the problem of routing bandwidth-guaranteed flows with time-varying bandwidth profiles on an MPLS network. We assume that each demand is routed in a fixed LSP, and that the amount of bandwidth that must be reserved along the LSP varies during the day according to a piece-wise mask which is known in advance. Such profiles can be explicitly declared by the VPN customers in the SLA, or, alternatively, predicted by the ISP based on past measurements. We propose a simple on-line algorithm based on shortest-path computation with link weights influenced by the residual peak bandwidth. We also provide an ILP formulation for the associated off-line problem, and adopt it as a reference performance bound for the on-line algorithm. The results presented show that the proposed algorithm, despite its simplicity, closely approximates the optimal solution. The paper shows that the a priori knowledge of the per-demand traffic profiles, still within a fixed routing framework, can be exploited to achieve a sensible bandwidth saving, and/or to differentiate bandwidth provisioning (and billing) on a per-hour basis
Distributed Schemes for Diverse Path Computation in Multi-Domain MPLS Networks
No full textMPLS is currently used by several JSPs to carry some high-value traffic components, such as telephony over IP trunks and VPNs. For this type of traffic, service availability is a critical QoS dimension that needs to be protected from network failures. With MPLS-TE, this can be achieved by means of path protection schemes, where active and backup LSPs are routed along diverse paths. Besides protection, path diversity can be exploited for load balancing, another common means of QoS improvement. In order to preserve other QoS requirements, the paths must meet certain constraints (e.g., bandwidth availability, low load) and/or minimize some metric (e.g., hop count). This requires the ability to establish path diversity in an optimal way. In many cases of practical interest, the QoS traffic has an interdomain scope. This is the case for ToIP and VPN traffic between different carriers, or between different ASs owned by the same carrier, as found, for example, after corporate acquisitions or mergers. Therefore, path diversity is a requirement for interdomain traffic engineering. In this work we address path diversity in a multidomain network, where individual domains are capable of connection-oriented forwarding and endowed with an MPLS-TE control plane. For administrative and/or scalability reasons intradomain routing information is not disseminated externally, so dynamic path computation must be achieved by a distributed scheme based on interdomain collaboration. We briefly describe three alternative schemes recently proposed for interdomain diverse path computation, and quantitatively assess their performance with simulations over real ISP topologies
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Routing demands with time-varying bandwidth profiles on a MPLS network
No full textIn this work we consider theproblem of routing bandwidth-guaranteed flows withtimW#(#(U:WT bandwidth profiles on a MPLS network. Weassum that eachdemUfl is routed in an explicitly routed LSP, and theamUxI of bandwidth that mat be reserved along the LSP varies during the day according to a piece-wisemiec which is known in advance. The tim#W#U:fl# bandwidth profiles can be explicitly declared by the VPNcustomIz in the SLA, or alternatively predicted by the ISP based on pastmtUI##flIU:fl# In this fram(xTU: we propose asimIfl on-linealgorithm foroptimW selection of LSP paths. We also provide an ILP formW#U:flW for the associated o#-line problem and adopt it as a referenceperformUWV bound for the on-line algorithm Additionally, wecomI#V theperformU:flI of fixed and variable routing in presence oftimfl#flU:flI#V bandwidth profiles. The results presented here suggest that the a priori knowledge of theper-demU: tra#c profiles can be exploited to achieve a fixed routing configuration, which can bemflxflflTU:I immflflT by variable reconfigurations. We relate our findings with a couple of previous works that in di#erent application contexts achievedsimeve results
Understanding Optimal Data Gathering in the Energy and Latency Domains of a Wireless Sensor Network
No full textThe problem of optimal data gathering in wireless sensor networks (WSNs) is addressed by means of optimization techniques. The goal of this work is to lay the foundations to develop algorithms and techniques that minimize the data gathering latency and at the same time balance the energy consumption among the nodes, so as to maximize the network lifetime. Following an incremental-complexity approach, several mathematical programming problems are proposed with focus on different network performance metrics. First, the static routing problem is formulated for large and dense WSNs. Optimal data-gathering trees are analyzed and the effects of several sensor capabilities and constraints are discussed, e.g., radio power constraints, energy consumption model, and data aggregation functionalities. Then, dynamic re-routing and scheduling are considered. An accurate network model is proposed that captures the tradeoff between the data gathering latency and the energy consumption, by modeling the interactions among the routing, medium access control and physical layers.For each problem, extensive simulation results are provided. The proposed models provide a deeper insight into the problem of timely and energy efficient data gathering. Useful guidelines for the design of efficient WSNs are derived and discussed
Variations on the Author
Full text link“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
Full text linkWe 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
Full text linkWe 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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