1,721,047 research outputs found
Better-Than-Best-Effort Class for the GEOCAST Project
No full textThis paper presents an access scheme for a class of service, named Better-than-Best-Effort (BBE), optimised for supporting non real-time traffic over a geostationary (GEO) satellite ATM (Asynchronous Transfer Mode) network. The BBE class has been designed to also efficiently support multicast traffic. In ATM frameworks, the IP traffic is mapped onto ATM connections, each one belonging to a pre-defined class of service and characterized by several QoS (Quality of Service) parameters, describing its behaviour in terms of the bandwidth and delay requirements. Since the traffic characteristics are often unknown (e.g., for most multicast and best-effort IP traffic), the connections of the proposed class of service require only two simple parameters: the amount of bandwidth to be reserved and the desired average delay. The reserved bandwidth is accessed on-demand, so that if the BBE connections do not request the full bandwidth, the leftover capacity can be distributed among the best-effort connections. Through the application of control theory methods, the Bandwidth-on-Demand (BoD) scheme developed for the BBE class of service can regulate usage of the satellite bandwidth to ensure the delay requirements. OPNET simulations have been executed to evaluate the impact of the proposed scheme
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
Network layer security: Design for a cross layer architecture
Get PDFTraditional modular layering schemes have served a major part in the development of a variety of protocols. However, as the physical layer impairments become more unpredictable, a cross layer design (CLD) which is dynamic in nature provides better performance. CLD introduces new challenges in protocol design as well as in the area of security. Using numerical analysis, we show that a link layer design employing header compression and cross layer signalling to protect protocol headers can limit packet discarding. This paper also reviews the IPsec protocol and describes how IPsec can be modified for cross layer architecture. © 2007 IEEE
A cross-layer architecture for satellite network security: CL-IPsec
Get PDFCross-layer architectures (CLAs) are proposed to improve performance in networks where physical layer impairments are unpredictable and provision of security services may be challenging, as in satellite networks. This paper proposes an extension to the IPsec protocol, named Cross-Layer IPsec (CL-IPsec), able to provide authentication and integrity services through a cross-layer architecture when the adopted protocol is UDP-Lite. This is suitable for multicast applications that are cost-effectively provided by satellite systems. A satellite emulation platform has been used to validate the CL-IPsec implementation and to evaluate the performance improvement derived from the proposed CLA. © 2008 IEEE
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
Multimedia traffic scheduling in DVB-S2 networks with mobile users
No full textDVB-S2 is a second-generation standard for satellite transmissions, developed to improve the performance of DVB-S. Recently, research efforts have been devoted to extend this standard for mobile usage. In this paper we consider a scenario composed of a Ku-band GEO bent-pipe satellite, a gateway and some mobile users. The interest is here in investigating the performance of a scheduling scheme to manage DVB-S2 resources on the forward channel for the delivery of video CBR and FTP traffic flows to mobile users. A novel scheduler scheme, called UBMT, has been proposed that aims to manage CBR packet transmission deadlines while maximizing the aggregated goodput. Simulation runs have permitted to validate the optimal performance achieved by UBMT in comparison with other schemes. The impact of different TCP versions has been investigated as well showing the good results obtained with the SACK option
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