1,720,974 research outputs found
An Analytical Study of the Resource Diffusion in Non-homogeneous P2P Networks
No full textOne of the most popular P2P application is file sharing. Its purpose is to spread out different contents, ranging from multimedia to data and software. In order to understand the dynamics of such application, it is important to study the movement of shared resources across the network. We consider a non-homogeneous distribution of the resources, by grouping peers into Autonomous Systems. We propose a probabilistic model that takes into account the peers behavior, and we exploit it to study the resource diffusion and the impact of freeloaders
Evaluation of different scheduling policies in IaaS applications by Mean Field analysis
No full textCloud Computing is emerging today as a commercial infrastructure that through the use of virtualization aims to provide on demand computing resources. In particular, the Infrastructure as a Service (IaaS) is a cloud service that allows the user to perform and execute any OS and application in virtual environments. In this work we present an evaluation of different policies for the assignment of virtual machines that IaaS providers can adopt in order to both efficiently planning their infrastructures and guaranteeing the quality of service expected by customers. The study is based on the exploitation of a Mean Field Model, able to evaluate systems with a relevant number of interacting entities, that can provide interesting insights derived from the computation of different performance indexes such as the request loss rate, the mean number of executing/available resources, and the overall ratio of satisfied requests to mention a few
Modelling Search, Availability, and Parallel Download in P2P File Sharing Applications with Fluid Model
No full textFile transfer using Peer-to-Peer file sharing applications is usually divided into two steps: resource search and resource download. Depending on the file size and its popularity, either of the two phases can become the bottleneck. In this paper we describe both the location and download phases of a generic Peer-to-Peer file sharing application using a fluid model. The proposed model allows the computation of the transfer time distribution, and it is capable of considering some advanced characteristic such as parallel downloads and on-off peer behavior. Model parameters reflect network, application, resource and user characteristics, and can be tuned to analyze a large number of different real Peer-to-Peer implementations.ile transfer using Peer-to-Peer file sharing applications is usually divided into two steps: resource search and resource download. Depending on the file size and its popularity, either of the two phases can become the bottleneck. In this paper we describe both the location and download phases of a generic Peer-to-Peer file sharing application using a fluid model. The proposed model allows the computation of the transfer time distribution, and it is capable of considering some advanced characteristic such as parallel downloads and on-off peer behavior. Model parameters reflect network, application, resource and user characteristics, and can be tuned to analyze a large number of different real Peer-to-Peer implementations
Modeling Biological Pathways: an Object-oriented like Methodology Based on Mean Field Analysis
No full textIn this paper we propose an object-oriented methodology based on Mean Field Analysis that can be used to describe in an intuitive manner the behavior of systems composed by a large number of interacting objects. For instance, this technique is well suited to study complex biopathways. We apply this approach to model the lac operon gene regulatory mechanism and glycolysis pathway. Numerical results obtained from the analysis of the model are presented
Analysis of Resource Transfers in Peer-to-Peer File Sharing Applications using Fluid Models
No full textThis paper proposes a stochastic fluid flow model to compute the transfer time distribution of resources in peer-to-peer file sharing applications. The amount of bytes transferred among peers is represented by a continuous quantity (the fluid level) whose flow rate is modulated by a set of discrete states representing the concurrent upload and download operations on the peers participating to the transfer. A transient solution of the model is then performed to compute the probability that a peer can download a given resource in less than t units of time as a function of several system parameters. In particular, the impact of file popularity, bandwidth characteristics, concurrent downloads and uploads, cooperation level among peers, and user behavior are included in our model specification. We also provide numerical results aiming at proving the potentialities of the approach we adopted as well as to investigate interesting issues related to the effect of incentive mechanisms on the user cooperation
On the Use of Petri Nets for the Computation of Completion Time Distributon for Short TCP Transfers
No full textIn this paper we describe how the completion time distribution for short TCP connections can be computed using Deterministic Stochastic Petri Net (DSPN) models of TCP protocol. A DSPN model of TCP is a representation of the finite state machine description of the TCP transmitter behavior, and provides an accurate description of the TCP dynamics. The DSPN requires as input only the packet loss probability, and the average round trip time for the TCP connections being considered. The proposed model has been validated by comparing it against simulation results in various network scenarios, thus proving that the model is accurate. Numerical results are presented to prove the flexibility and the potentialities of the proposed methodology
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No full textFixed Point Approximations for TCP Behavior in Networks of Routers
No full textIn this paper we use fixed point methods to model the behavior of a population of TCP fows traversing a network of routers implementing either Drop Tail or the RED queue management policies. We formulate a non-linear problem with the router average queue lengths as unknowns. Once the average queue lengths are obtained, other metrics such as router loss probability, TCP flow throughput, TCP flow end-to-end loss rates, and average round trip time can be easily obtained. Comparison with simulation for a variety of scenarios shows that the model is quite accurate in its predictions
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
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