1,720,958 research outputs found
Analysis and Enhancement of TCP Vegas Congestion Control in a Mixed TCP Vegas and TCP Reno Network Scenario
No full textIts more refined congestion control mechanisms, also based on the estimation of round trip delays, allow TCP Vegas to outperform the more widespread TCP Reno congestion control, based only on the packet loss detection, in a number of network environments. However, these mechanisms make TCP Vegas less aggressive with respect to TCP Reno; thereby TCP Vegas sources show high weakness in taking the available bandwidth when competing with other TCP Reno sources. This is a major reason that hinders the spread of TCP Vegas among Internet users. In this work, after a preliminary analytic study about the limits of TCP Vegas in mixed network environments, we describe a new adaptive mechanism for TCP Vegas, called TCP NewVegas, designed in order to improve its performance even in heterogeneous network scenarios. The large number of simulations, presented in this paper, show that TCP NewVegas guarantees good performance even in mixed network environments, without canceling the desirable features (e.g. fairness) that TCP Vegas exhibits in homogeneous environments. © 2003 Elsevier Science B.V. All rights reserved
TCP over wireless links with Rayleigh fading: some considerations about energy efficiency and TCP performance
No full textAntwerp (B
Experimental Analysis of TCP and UDP Traffic Performance over Infra-structured 802.11b WLANs
No full textIn this paper we present the results of experiments carried out in an infra-structured 802.11b WLAN comprising a single Access Point (AP) and a number of user terminals. The aim of this work is twofold: by the one hand, we validate well-known ¿TCP (UDP) over 802.11¿ analytic models by means of experimental results; by the other hand, we focus our analysis on TCP behavior over 802.11b. We present results about flow fairness, about interaction between WLAN link layer parameters (ARQ) and transport protocols and about TCP flows traffic characteristics. With respect to earlier related works, an added value of our analysis is given by a more accurate knowledge and control of key parameters that highly affect the system performance (e.g., mobile station transmission bitrate, maximum number of retransmission attempts, TCP version, etc.) that guarantees the reliability of numerical results. This is a key issue in order to confidently explain observed experimental phenomena
Simple Models and their Limits for TCP/IP Network Analysis and Dimensioning
No full textThe analysis and design of TCP/IP networks is a key component in the development of the Internet. We consider how simple analytical modelling of the key network elements can yield sufficiently accurate performance results by means of simulations with actual TCP sources. The defined modelling approach, named the fixed point model, is exploited to state a dimensioning problem of an IP network dominated by TCP traffic. The procedure for the TCP/IP network capacity dimensioning is based on the definition of a user satisfaction index, suitable for a best-effort scenario
Investigating TCP Single Source Behavior in Time-Varying Capacity Network Scenarios
No full textSome recent simulation works have pointed out that TCP appears to suffer the variability of the available bandwidth when it shares the network resources with higher priority traffic. This paper describes an analytic model able to reproduce TCP behavior under a time-varying available capacity. The aim is to investigate the interaction between TCP and high-priority real-time traffic (e.g., voice and video). The accuracy of the model against simulations is shown to be satisfactory and superior with respect to other popular TCP models in a definite range of network scenarios. Besides, by means of the proposed model and the several simulations carried out in this work we gain air interesting insight on TCP behavior in the considered network environment
Investigating interactions between ARQ mechanisms and TCP over wireless links
No full textIn this paper we investigate interactions
between TCP and wireless ARQ mechanisms. The aim
is to understand what is the best conguration of the
wireless link protocol in order to guarantee TCP performance,
seemingly a controversial issue. Interactions between
TCP and different link layer mechanisms are evaluated
by means of an analytic model, that reproduces a
generic selective repeat ARQ protocol (widely used in the
current wireless environments) and the TCP behavior in a
wired-cum-wireless network scenario. A numerical investigation
is carried out in a specic case study (TCP over
3G radio access) by means of simulations collected with
a very detailed UMTS-TDD simulator based on ns. Our
main nding is that fully reliable ARQ protocols are the
best choices from the TCP perspective; in fact, whereas a
residual packet loss left over by not fully reliable ARQ protocols
may not degrade appreciably TCP throughput performance
as long as it is a fraction of the overall end-to-end
TCP packet loss, no apparent performance advantages (e.g.
energy savings) come from limiting the numbe
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
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
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