116 research outputs found
Peer Selection in Peer-to-Peer Streaming Systems
One important task of any peer-to-peer streaming system (p2p-ss)
is how to choose which peers should connect to which peers. How
well a p2p-ss perform this task greatly influences its performance.
This thesis explores how different peer selection algorithms
affect the performance of such systems.
A framework for doing the comparisons of peer selection algorithms
is built on top of the network simulator ns2, making it possible to
later extend the simulations with new peer selection algorithms,
congestion control algorithms, wireless networks, cross traffic and
other. However, ns2 is a low-level simulator, hence limiting the
number of peers in the simulations, because CPU-resources are limited.
The simulations are limited to single-layered streams.
We find that a centralized selection method, which utilizes knowledge
of bandwidth capacities and routing in the network, greatly
outperforms both simple random selection of peers, and selection of
close peers. Even though centralized selection does not scale well,
and is therefore only applicable for a limited number of peers, this
shows there is much room for improvement over basic strategies
Group-based reduction schemes for streaming applications
Some peer-to-peer streaming systems make use of linear codes to reduce the rate of the data uploaded by peers with limited upload capabilities. Such "data reduction" techniques are based on a vector-space approach and produce the data to be uploaded by means of linear combinations of the content data in a suitable finite field. In this paper, we propose a more general approach based on group theory. The
new approach, while including the vector space approach as a special case, allows to design schemes that cannot be modeled as linear codes. We analyze the properties of the schemes based on the new approach, showing also how a group-based scheme can be used to prevent stream poisoning and how a group-based scheme can be converted into a secret-sharing scheme. Examples of group-based schemes that cannot be described in the vector-space framework are also shown
Access-Network Association Policies for Media Streaming in Heterogeneous Environments
We study the design of media streaming applications in the presence of
multiple heterogeneous wireless access methods with different throughputs and
costs. Our objective is to analytically characterize the trade-off between the
usage cost and the Quality of user Experience (QoE), which is represented by
the probability of interruption in media playback and the initial waiting time.
We model each access network as a server that provides packets to the user
according to a Poisson process with a certain rate and cost. Blocks are coded
using random linear codes to alleviate the duplicate packet reception problem.
Users must take decisions on how many packets to buffer before playout, and
which networks to access during playout. We design, analyze and compare several
control policies with a threshold structure. We formulate the problem of
finding the optimal control policy as an MDP with a probabilistic constraint.
We present the HJB equation for this problem by expanding the state space, and
exploit it as a verification method for optimality of the proposed control law.Comment: submitted to CDC 201
Peer-to-peer multimedia communication
I sistemi Peer-to-Peer (P2P) sono stati inventi, messi in campo e studiati da più di
dieci anni, andando al di là della semplice applicazione per scambio di file. Nelle reti P2P i partecipanti
si organizzano in una rete "overlay" che è astratta rispetto alle caratteristiche della sottostante rete fisica.
Scopo di questi sistemi è la distribuzione di risorse quali contenuti, spazio di memorizzazione o cicli macchina. Gli utenti quindi giocano un ruolo attivo e possono essere considerati come sia clienti che serventi allo stesso tempo per il particolare servizio che la rete P2P offre.
Lo scopo di questa tesi di dottorato è lo studio di questi sistemi ed il dare un contributo nella loro analisi
prestazionale. L'analisi mira a valutare le prestazioni raggiunte dai sistemi e/o i limiti teorici raggiungibili.
Infatti, nonostante esistano diversi meccanismi per il peer-to-peer streaming, l'analisi prestazionale di questo tipo di sistemi può essere considerata ancora nella sua infanzia. A questo scopo, i contributi principali di questa tesi di dottorato sono: i)la derivazione di un limite teorico per il ritardo nei sistemi di
P2P streaming, ii) la creazione di un algoritmo che sfrutti le conoscenze acquisite attraverso il lavoro teorico, iii) l'analisi prestazionale dell'algoritmo utilizzando un simulatore espressamente progettato per riprodurre le caratteristiche delle reti P2P reali composte da centinaia di migliaia di nodi che si connettono e disconnettono in continuazione.Peer-to-Peer (P2P) systems have been invented, deployed and researched for more
than ten years and went far beyond the simple file sharing applications. In P2P
networks, participants organize themselves in an overlay network that abstracts
from the topological characteristics of the underlying physical network. Aim of
these systems is the distribution of some kind of resources like contents, storage, or
CPU cycles. Users, therefore, play an active role so that they can be considered
as client and server at the same time, for the particular service that is provided
through the P2P paradigm.
Goal of this dissertation thesis is to study
these systems, and give contributes in their performance evaluation. The analysis
will aim to evaluate the achieved performance of a system and/or the performance
bounds that could be achievable.
In fact, even if there are several proposals of different systems, peer-to-peer
streaming performance analysis can be considered still in its infancy and there is
still a lot of work to do. To this aim, the main contributes of this dissertation thesis
are i) the derivation of a theoretical delay bounds for P2P streaming system ii)
II
the creation of an algorithm that exploits the new insights that come out from the
theoretical study iii) the performance evaluation of this algorithm using an ad-hoc
simulator, expressly tailored to reproduce the characteristics of the real-world P2P
streaming systems, composed by hundred thousands of intermittently connected
users
VOD STREAMING WITH A NETWORK CODING EQUIVALENT CONTENT DISTRIBUTION SCHEME
Although random access operations are desirable for on-demand video streaming in peer-to-peer systems, they are difficult to efficiently achieve due to the asynchronous interactive behaviors of users and the dynamic nature of peers. In this paper, we propose a network coding equivalent content distribution (NCECD) scheme to efficiently handle interactive videoon- demand (VoD) operations in peer-to-peer systems. In NCECD, videos are divided into segments that are then further divided into blocks. These blocks are encoded into independent blocks that are distributed to different peers for local storage. With NCECD, a new client only needs to connect to a sufficient number of parent peers to be able to view the whole video and rarely needs to find new parents when performing random access operations. In most existing methods, a new client must search for parent peers containing specific segments; however, NCECD uses the properties of network coding to cache equivalent content in peers, so that one can pick any parent without additional searches. Experimental results show that the proposed scheme achieves low startup and jump searching delays and requires fewer server resources. In addition, we present the analysis of system parameters to achieve reasonable block loss rates for the proposed scheme
Scalable Peer-to-Peer Streaming for Live Entertainment Content
We present a system for streaming live entertainment content over the Internet originating from a single source to a scalable number of consumers without resorting to centralized or provider-provisioned resources. The system creates a peer-to-peer overlay network, which attempts to optimize use of existing capacity to ensure quality of service, delivering low startup delay and lag in playout of the live content. There are three main aspects of our solution: first, a swarming mechanism that constructs an overlay topology for minimizing propagation delays from the source to end consumers; second, a distributed overlay anycast system that uses a location-based search algorithm for peers to quickly find the closest peers in a given stream; and finally, a novel incentive mechanism that encourages peers to donate capacity even when the user is not actively consuming content
Avoiding Interruptions - QoE Trade-offs in Block-coded Streaming Media Applications
We take an analytical approach to study Quality of user Experience (QoE) for
video streaming applications. First, we show that random linear network coding
applied to blocks of video frames can significantly simplify the packet
requests at the network layer and save resources by avoiding duplicate packet
reception. Network coding allows us to model the receiver's buffer as a queue
with Poisson arrivals and deterministic departures. We consider the probability
of interruption in video playback as well as the number of initially buffered
packets (initial waiting time) as the QoE metrics. We characterize the optimal
trade-off between these metrics by providing upper and lower bounds on the
minimum initial buffer size, required to achieve certain level of interruption
probability for different regimes of the system parameters. Our bounds are
asymptotically tight as the file size goes to infinity.Comment: Submitted to ISIT 2010 - Full versio
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