1,720,972 research outputs found
Megalos: A scalable architecture for the virtualization of large network scenarios
Full text linkWe introduce an open-source, scalable, and distributed architecture, called Megalos, that supports the implementation of virtual network scenarios consisting of virtual devices (VDs) where each VD may have several Layer 2 interfaces assigned to virtual LANs. We rely on Docker containers to realize vendor-independent VDs and we leverage Kubernetes for the management of the nodes of a distributed cluster. Our architecture does not require platform-specific configurations and supports a seamless interconnection between the virtual environment and the physical one. Also, it guarantees the segregation of each virtual LAN traffic from the traffic of other LANs, from the cluster traffic, and from Internet traffic. Further, a packet is only sent to the cluster node containing the recipient VD. We produce several example applications where we emulate large network scenarios, with thousands of VDs and LANs. Finally, we experimentally show the scalability potential of Megalos by measuring the overhead of the distributed environment and of its signaling protocols
MRT: A Fast Multi-Threaded MRT Parser
No full textBGP is the inter-domain routing protocol of the Internet. BGP routers exchange BGP Updates, and adjust their routing table to reflect changes in the network. A wide variety of research and operational projects leverage on massive processing of BGP Updates, so it is crucial to analyse such data in the most efficient way. Hence, different MRT parsers have been developed. Most of them are unsuitable for big data analyses due to various limitations. In this paper, we present MRT, a multi-threaded MRT parser library written in C. We show its architecture, a performance comparison with other MRT parsers, and its possible integration into a data processing pipeline
VFTGen: A Tool to Perform Experiments in Virtual Fat Tree Topologies
No full textData centers are a critical part of the Internet infrastructure. In fact, most of the relevant online services are hosted in a data center. Data center networks are complex, since they are characterized by a high density architecture and by a high level of redundancy. Fat tree topologies are currently the most used in hyperscale data centers. Performing tests in such topologies would be unfeasible, because of the high costs of the required equipment and due to the involvement of human resources. This would limit the automation and reproducibility of tests, leading to a more error-prone testing pipeline. This paper presents VFTGen, a tool that, leveraging on the virtualization and the Software Defined Data Center concepts, automatically builds, deploys and configures arbitrary fat tree topologies in a virtual environment. We demonstrate the ease of use of the tool and its value as a support to the study or the development of networking protocols for fat trees
Kathará: A Lightweight Network Emulation System
No full textIn computer networks, tests to ensure the correct behaviour of network equipment or protocols are often required. Because of the high cost of physical hardware, these tests are always performed in a virtual environment. Kathará is a network emulation system which accurately reproduces the behaviour of a real system. It can exploit several virtualization technologies leveraging on its modularity. Lately, Kathará has been rewritten to overcome some implementation limitations and performance issues. This paper presents the Kathará model and its new architecture, demonstrating its value, comparing its scalability and performance with Netkit (another state-of-the-art tool for network emulation) and with the previous version of Kathará
Long-Lasting Sequences of BGP Updates
No full textThe Border Gateway Protocol (BGP) is the protocol that makes the various networks composing the Internet communicate to each other. Routers speaking BGP exchange updates to keep the routing up-to-date and allow such communication. This usually is done to reflect changes in the routing configurations or as a consequence of link failures. In the Internet as a whole it is normal that BGP updates are continuously exchanged, but for any specific IP prefix, these updates are supposed to be concentrated in a short time interval that is needed to react to a network change. On the contrary, in this paper we show that there are many IP prefixes involved in quite long sequences consisting of a large number of BGP updates. Namely, examining ∼ 30 billion updates collected by 172 observation points distributed worldwide, we estimate that almost 30 % of them belong to sequences lasting more than one week. Such sequences involve 222285 distinct IP prefixes, approximately one fourth of the number of announced prefixes. We detect such sequences using a method based on the Discrete Wavelet Transform. We publish an online tool for the exploration and visualization of such sequences, which is open to the scientific community for further research. We empirically validate the sequences and report the results in the same online resource. The analysis of the sequences shows that almost all the observation points are able to see a large amount of sequences, and that 53 % of the sequences last at least two weeks
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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