1,720,959 research outputs found
Traffic analysis at short time-scales: an empirical case study from a 3G cellular network
No full textThe availability of synchronized packet-level traces
captured at different links allows the extraction of one-way delays
for the network section in between. Delay statistics can be used
as quality indicators to validate the health of the network and to
detect global performance drifts and/or localized problems. Since
packet delays depend not only on the network status but also on
the arriving traffic rate, the delay analysis must be coupled with
the analysis of the traffic patterns at short time scales.
In this work we report on the traffic and delay patterns
observed at short timescales in a 3G cellular mobile network.
We show that the aggregate traffic rate exhibits large impulses
and investigate on their causes. Specifically, we find that highrate
sequential scanners represent a common source of traffic
impulses, and identify the potential consequences of such traffic
onto the underlying network.
This case-study demonstrates that the microscopic analysis of
delay and traffic patterns at short time-scales can contribute
effectively to the task of troubleshooting IP networks. This is
particularly important in the context of 3G cellular networks
given their complexity and relatively recent deployment
On the Impact of Unwanted Traffic onto a 3G Network
No full textThe presence of "unwanted" (or background) traffic in the Internet is a well-known fact. In principle any network that has been engineered without taking into account the presence of unwanted traffic might experience troubles during periods of massive exposure to it, e.g. large-scale infections. A concrete example was provided by the spreading of Code-Red-II in 2001, which caused several routers crashes worldwide. Similar events might take place in 3G networks as well, with further potential complications due to the functional complexity and the scarcity of radio resources. In this explorative paper, we show that unwanted traffic is present also in GPRS/UMTS, mainly due to the widespread use of 3G connect cards for laptops. Based on a mixture of real-world measurements and theoretical speculations, we investigate the potential impact of such traffic onto the underlying network. We show that under certain hypothetical network configuration settings unwanted traffic, and specifically scanning traffic from infected mobile stations, can cause large-scale wastage of logical resources, and in extreme cases starvation. We urge the research community and network operators to consider the issue of 3G robustness to unwanted traffic as a prominent research area. The goal of this paper is to trigger interest and at the same time move a first pioneering step in this direction
Composition of GPRS/UMTS traffic : snapshots from a live network
No full textThis paper focuses on the traffic composition in a real GPRS/UMTS
network. We present results from two datasets covering two one-week measurement periods, in December 2004 and November 2005. We show how users and traffic split between access technologies (GPRS and UMTS) and services, and present an analysis of the per-user activity at the PDP-context level.
The results reported here provide an up-to-date view of the traffic and user activity in an operational 3G network. It should help those researchers interested in reproducing synthetic network scenarios to gain a better understanding about the traffic environment in a real network. Moreover, we discuss several technicalities found in performing such measurements, which should be helpful to those researchers active in 3G monitoring
Measurement-based Optimization of a 3G Core Network: A Case Study
No full textWe consider the optimization of the Core Network section of a mobile cellular network. While we focus on GPRS the proposed method can be applied to UMTS as well. The problem is to find an optimal assignment of PCUs (Packet Control Units, a module of the BSC) to SGSNs based on measured data. Two concurrent optimization goals apply: balance the number attached Mobile Stations among the available SGSNs, and at the same time minimize the inter-SGSN Routing Area Updates. The input data for the optimization can be extracted from the live tra#c signaling by passively monitoring the Gb links between the PCUs and SGSNs. We show how to estimate the mobility matrix and the distribution of attached Mobile Stations for each Routing Area, and how to clean-up the data at hand. A novel ILP formulation is provided for the (re)assignment problem. We present exemplary numerical results for a case study based on real traces from an operational network
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
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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