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Video broadcasting in reti dinamiche: opportunità dei sistemi peer-to-peer live streaming
No full textIl traffico IP determinato dalle applicazioni video sta crescendo esponenzialmente, questo è attribuibile alla diffusione di dispositivi quali tablet, smartphone, smartTV. Contemporaneamente la diffusione della tecnologia over the top (OTT) streaming, cioè la distribuzione di contenuti video su Internet utilizzando i comuni protocolli di trasporto dati, ha permesso a soggetti diversi dai soli operatori di telecomunicazioni di inserirsi in questo mercato. Tale tecnologia non utilizza una rete dedicata, talvolta può accadere che la larghezza di banda disponibile sia inferiore a quella necessaria al video streaming, determinando così una degradazione della qualità video. Lo standard Dynamic Adaptive Streaming over HTTP (DASH) recentemente proposto, prevede di distribuire diverse versioni dello stesso contenuto per poter dinamicamente adattare la bitrate alle condizioni di rete, e alle diverse capacità degli user devices.
In questo contesto, mi sono concentrata sulle opportunità offerte dai sistemi di streaming peer-to-peer (P2P): la cooperazione tra peer garantisce costi infrastrutturali ridotti e maggiore scalabilità e flessibilità.
Dapprima, ho investigato come una piattaforma live P2P possa trarre vantaggio dalla presenza di spettatori assidui, fornendo loro un servizio più soddisfacente rispetto ai quelli saltuari, e come questi utenti favoriti siano preservati anche quando il sistema si trova in condizioni critiche di funzionamento. Ho classificato gli utenti in base al loro comportamento, per poi alterare l'algoritmo di scheduling dei chunk richiesti, in modo da servire con priorità gli utenti assidui, fornendo loro un servizio di qualità migliore e un più rapido accesso al canale. É stato sviluppato un modello analitico che descrive lo startup delay, per cogliere il miglioramento introdotto dalla modifica proposta. I risultati ottenuti indicano una evidente differenziazione di servizio e dimostrano che quando la larghezza di banda scarseggia, agli utenti assidui è comunque garantito un servizio di qualità.
Successivamente, per garantire agli utenti una migliore qualità di servizio, ho proposto di combinare architettura P2P e DASH, sfruttando la prooprietà di cooperazione della prima e la capacità di adattatività del secondo, in una nuova piattaforma P2P-DASH, che consiste in più overlay, ognuna delle quali distribuisce una differente rappresentazione DASH. Ho sviluppato un algoritmo di controllo distribuito che determina quale rappresentazione un peer deve scaricare in base alla qualità video percepita e lo stato di salute della intera overlay, così da ottenere un duplice obiettivo: buona qualità video per l'utente e buon funzionamento per l'intero sistema.
L'efficacia della soluzione è dimostrata attraverso la simulazione e indica che il sistema P2P-DASH è in grado di garantire agli utenti buone prestazioni, migliori rispetto a un sistema P2P, che non usi il DASH a parità di risorse e di richieste. Il sistema è stato studiato in presenza di un evento critico quale il flash-crow, evidenziando come un massiccio arrivo di nuovi utenti possa essere prontamente rilevato e gestito.
In fine, ho posto particolare attenzione alla riduzione dello switching delay, ossia il ritardo sperimentato dal peer quando transita da una overlay all'altra. A questo scopo, ho introdotto alcuni specifiche azioni: (i) estensione della neighborhood dei peer in modo da sapere in anticipo la posizione del processo di streaming della overlay target; (ii) priorità di servizio alle richieste di video chunk dei nodi appena arrivati nella overlay, e (iii) nuovo algoritmo di controllo che garantisca più risorse alle overlay che distribuiscono streaming rate più elevate, per ridurre il disallineamento dei processi di streaming tra le varie overlay. I risultati hanno dimostrato che tutte le azioni sono efficaci per la riduzione dello switching delay.IP traffic due to video applications is exponentially growing, thanks to the diffusion of devices such as tablets, smartphones and smart TVs. At the same time, the over the top (OTT) streaming diffusion, namely the diffusion of video and audio contents over the Internet employing the conventional data transport protocols, has allowed subjects different from telco operators to penetrate this market. These technologies do not employ a dedicated network and it may therefore happen that the current available bandwidth is lower than the one requested to relay the video, determining a degradation in viewing quality. The video source has therefore be adaptive; to this regard, the Dynamic Adaptive Streaming over HTTP (DASH) standard has been recently proposed, as it providing different versions of the same media content to adapt the delivery process over the Internet to dynamic network conditions and different user device capabilities.
Within this context, I focused on the opportunities offered by peer-to-peer (P2P) system for live streaming: the cooperation among peers guarantees reduced infrastructural cost and greater scalability and flexibility.
At first, I investigated how a p2p television platform can take advantage of the presence of frequent channel viewers to grant them a more satisfying service than to less regular spectators, and how such favorite users can also be protected when unfavorable operating conditions occur. I classified the users on the basis of their behaviour, in order to alter the video chunk scheduling algorithm, with the aim of serving frequent users in a privileged manner, providing them with a better viewing experience and a faster access to the channel. An analytical model to describe the startup delay was developed, to capture the improvement that the proposed modification introduces. The obtained results show that a service differentiation is attained and demonstrate that, even if bandwidth resources become scarce, a good service is granted to frequent users.
Next, to provide users with a better viewing experience, I proposed to jointly exploit DASH adaptivity and the P2P cooperation property in a new P2P-DASH platform, that consists of several swarms, each of them delivering a different DASH representation. I devised a new distributed rate control strategy that determines which video version the user downloads on the basis of both the current viewing quality experienced and the overlay health status, so as to achieve a twofold goal: good user viewing quality and good functioning of the whole system.
The effectiveness of the solution has been demonstrated through simulation and it indicates that the P2P-DASH platform is able to grant its users a good performance, better than in a DASH-unaware P2P platform subject to the same streaming requests and with the same available resources. System behavior has been investigated in the critical condition of a flash crowd, showing that the massive arrival of new users can be promptly revealed and gradually accommodated.
At the end, I paid particular attention to reducing the switching delay, that is, the delay incurred by the peer when transiting from one representation to another. To achieve this goal, I introduced some specific actions:(i) extension of the peer neighborhood in order to know in advance the position of streaming process in the target overlay; (ii) priority scheduling to serve first the video chunk requests of the new nodes entering the overlay and (iii) new rate control algorithm able to guarantee more resources to overlays that deliver higher streaming rates, therefore reducing the misalignment among streaming processes in different overlays. The simulation results have demonstrated the effectiveness of all these actions in confining the switching delay, and have numerically quantified the influence that different actions exhibit
Successfully Mapping DASH over a P2P Live Streaming Architecture
No full textThis work proposes to combine Peer-to-Peer (P2P) and Dynamic Adaptive Streaming over HTTP (DASH), leveraging the scalability and self-organization properties of the former and the capability of the latter to adapt the rate of the delivered video to varying operating conditions. The devised P2P-DASH architecture is a multi-overlay P2P platform, where every peer implements a decentralized rate control strategy that steers its transitions from one overlay to another, so as to achieve a good viewing quality and also preserve the good functioning of the entire system. At peer’s site, the new architecture displays the following salient features: (i) an augmented pool of neighbors, to provide every node with the knowledge of the streaming process within adjacent overlays; (ii) a priority mechanism to speed up the delivery of video chunks to peers that newly enter the system or switch from the current to a new overlay, in order to quickly turn them into active peers; (iii) some alternative rate control algorithms to guarantee, with different degrees, more resources to overlays that deliver higher streaming rates, therefore reducing the misalignment among streaming processes which occur in different overlays, and ultimately improve the viewing quality of the single user. System behavior is extensively investigated through simulation and some clear design guidelines are provided
Adaptive Streaming in P2P Live Video Systems: a Distributed Rate Control Approach
No full textDynamic Adaptive Streaming over HTTP (DASH) is a recently proposed standard that offers different versions
of the same media content to adapt the delivery process over the Internet to dynamic bandwidth fluctuations
and different user device capabilities. The peer-to-peer (P2P) paradigm for video streaming allows
to leverage the cooperation among peers, guaranteeing to serve video requests with increased scalability
and reduced cost. We propose to combine these two approaches in a P2P-DASH architecture, exploiting the
potentiality of both. The new platform is made of several swarms and a different DASH representation is
streamed within each of them; unlike client-server DASH architectures, where each client autonomously
selects which version to download according to current network conditions and to its device resources, we
put forth a new rate control strategy implemented at peer site to maintain a good viewing quality to the
local user and to simultaneously guarantee the successful operation of the P2P swarms. The effectiveness
of the solution is demonstrated through simulation and it indicates that the P2P-DASH platform is able to
warrant its users a very good performance, much more satisfying than in a conventional P2P environment
where DASH is not employed. Through a comparison with a reference DASH system modeled via the Integer
Linear Programming (ILP) approach, the new system is shown to outperform such reference architecture.
To further validate the proposal, both in terms of robustness and scalability, system behavior is investigated
in the critical condition of a flash crowd, showing that the strong upsurge of new users can be successfully
revealed and gradually accommodated
An IP-TV P2P streaming system that improves the viewing quality and confines the startup delay of regular audience
No full textThis paper investigates how a p2p television platform can take advantage of the presence of frequent channel viewers to grant them a more satisfying service than to less regular spectators, and how such privileged users can also be protected when unfavorable operating conditions manifest within the overlay. The explored idea is to learn beforehand about the users’ interests, monitoring their behavior in the recent past, in order to cluster them in groups that display different habits; then, the video chunk scheduling algorithm of the overlay is altered, with the aim of serving frequent spectators in a privileged manner, providing them with a better viewing experience and a faster access to the selected channel without overly penalizing less habitual customers. An analytical model is developed, to capture the difference in average startup delay that the proposed modifications introduce; several additional performance metrics are numerically determined, in order to thoroughly size up the performance of both groups of viewers. The obtained results show that a clear service differentiation is attained and demonstrate that, if bandwidth resources become scarce, frequent viewers are protected and still enjoy a broadcasting service of superior quality
A Novel Rate Control Strategy for Adaptive Video Streaming in P2P Overlays
No full textThis work proposes a novel P2P-DASH architecture that jointly leverages the intrinsic cooperation property of P2P and the adaptivity of Dynamic Adaptive Streaming over HTTP (DASH) to deliver videos to a large population of users with heterogeneous streaming requests. The system is made of several overlays, each distributing a different DASH representation; every peer within the system autonomously enforces a newly devised rate control strategy that steers its movements from one overlay to another, in order to maintain a good viewing experience and to simultaneously guarantee the successful operation of the P2P overlays. The effectiveness of the solution is demonstrated through simulation and it indicates that the P2P-DASH platform is able to guarantee its users a very good performance, much more satisfying than in a conventional P2P environment where DASH is not employed. Moreover, through the comparison with a reference system modeled via the Integer Linear Programming (ILP) approach,it is shown that our system outperforms such reference architecture in terms of viewing quality; at the same time, the number of users streaming the video at the desired bit rate is extremely close to the optimum of the ILP setting in the most favorable scenarios, and only moderately suboptimal in the worst
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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