9,119 research outputs found
On the stability of two-chunk file-sharing systems
We consider five different peer-to-peer file sharing systems with two chunks,
with the aim of finding chunk selection algorithms that have provably stable
performance with any input rate and assuming non-altruistic peers who leave the
system immediately after downloading the second chunk. We show that many
algorithms that first looked promising lead to unstable or oscillating
behavior. However, we end up with a system with desirable properties. Most of
our rigorous results concern the corresponding deterministic large system
limits, but in two simplest cases we provide proofs for the stochastic systems
also.Comment: 19 pages, 7 figure
Mode-Suppression: A Simple, Stable and Scalable Chunk-Sharing Algorithm for P2P Networks
The ability of a P2P network to scale its throughput up in proportion to the
arrival rate of peers has recently been shown to be crucially dependent on the
chunk sharing policy employed. Some policies can result in low frequencies of a
particular chunk, known as the missing chunk syndrome, which can dramatically
reduce throughput and lead to instability of the system. For instance, commonly
used policies that nominally "boost" the sharing of infrequent chunks such as
the well known rarest-first algorithm have been shown to be unstable. Recent
efforts have largely focused on the careful design of boosting policies to
mitigate this issue. We take a complementary viewpoint, and instead consider a
policy that simply prevents the sharing of the most frequent chunk(s).
Following terminology from statistics wherein the most frequent value in a data
set is called the mode, we refer to this policy as mode-suppression. We also
consider a more general version that suppresses the mode only if the mode
frequency is larger than the lowest frequency by a fixed threshold. We prove
the stability of mode-suppression using Lyapunov techniques, and use a Kingman
bound argument to show that the total download time does not increase with peer
arrival rate. We then design versions of mode-suppression that sample a small
number of peers at each time, and construct noisy mode estimates by aggregating
these samples over time. We show numerically that the variants of
mode-suppression yield near-optimal download times, and outperform all other
recently proposed chunk sharing algorithms
A Stable Fountain Code Mechanism for Peer-to-Peer Content Distribution
Most peer-to-peer content distribution systems require the peers to privilege
the welfare of the overall system over greedily maximizing their own utility.
When downloading a file broken up into multiple pieces, peers are often asked
to pass on some possible download opportunities of common pieces in order to
favor rare pieces. This is to avoid the missing piece syndrome, which throttles
the download rate of the peer-to-peer system to that of downloading the file
straight from the server. In other situations, peers are asked to stay in the
system even though they have collected all the file's pieces and have an
incentive to leave right away.
We propose a mechanism which allows peers to act greedily and yet stabilizes
the peer-to-peer content sharing system. Our mechanism combines a fountain code
at the server to generate innovative new pieces, and a prioritization for the
server to deliver pieces only to new peers. While by itself, neither the
fountain code nor the prioritization of new peers alone stabilizes the system,
we demonstrate that their combination does, through both analytical and
numerical evaluation.Comment: accepted to IEEE INFOCOM 2014, 9 page
Statistical Modelling of Information Sharing: Community, Membership and Content
File-sharing systems, like many online and traditional information sharing
communities (e.g. newsgroups, BBS, forums, interest clubs), are dynamical
systems in nature. As peers get in and out of the system, the information
content made available by the prevailing membership varies continually in
amount as well as composition, which in turn affects all peers' join/leave
decisions. As a result, the dynamics of membership and information content are
strongly coupled, suggesting interesting issues about growth, sustenance and
stability.
In this paper, we propose to study such communities with a simple statistical
model of an information sharing club. Carrying their private payloads of
information goods as potential supply to the club, peers join or leave on the
basis of whether the information they demand is currently available.
Information goods are chunked and typed, as in a file sharing system where
peers contribute different files, or a forum where messages are grouped by
topics or threads. Peers' demand and supply are then characterized by
statistical distributions over the type domain.
This model reveals interesting critical behaviour with multiple equilibria. A
sharp growth threshold is derived: the club may grow towards a sustainable
equilibrium only if the value of an order parameter is above the threshold, or
shrink to emptiness otherwise. The order parameter is composite and comprises
the peer population size, the level of their contributed supply, the club's
efficiency in information search, the spread of supply and demand over the type
domain, as well as the goodness of match between them.Comment: accepted in International Symposium on Computer Performance,
Modeling, Measurements and Evaluation, Juan-les-Pins, France, October-200
A stochastic epidemiological model and a deterministic limit for BitTorrent-like peer-to-peer file-sharing networks
In this paper, we propose a stochastic model for a file-sharing peer-to-peer
network which resembles the popular BitTorrent system: large files are split
into chunks and a peer can download or swap from another peer only one chunk at
a time. We prove that the fluid limits of a scaled Markov model of this system
are of the coagulation form, special cases of which are well-known
epidemiological (SIR) models. In addition, Lyapunov stability and settling-time
results are explored. We derive conditions under which the BitTorrent
incentives under consideration result in shorter mean file-acquisition times
for peers compared to client-server (single chunk) systems. Finally, a
diffusion approximation is given and some open questions are discussed.Comment: 25 pages, 6 figure
A New Stable Peer-to-Peer Protocol with Non-persistent Peers
Recent studies have suggested that the stability of peer-to-peer networks may
rely on persistent peers, who dwell on the network after they obtain the entire
file. In the absence of such peers, one piece becomes extremely rare in the
network, which leads to instability. Technological developments, however, are
poised to reduce the incidence of persistent peers, giving rise to a need for a
protocol that guarantees stability with non-persistent peers. We propose a
novel peer-to-peer protocol, the group suppression protocol, to ensure the
stability of peer-to-peer networks under the scenario that all the peers adopt
non-persistent behavior. Using a suitable Lyapunov potential function, the
group suppression protocol is proven to be stable when the file is broken into
two pieces, and detailed experiments demonstrate the stability of the protocol
for arbitrary number of pieces. We define and simulate a decentralized version
of this protocol for practical applications. Straightforward incorporation of
the group suppression protocol into BitTorrent while retaining most of
BitTorrent's core mechanisms is also presented. Subsequent simulations show
that under certain assumptions, BitTorrent with the official protocol cannot
escape from the missing piece syndrome, but BitTorrent with group suppression
does.Comment: There are only a couple of minor changes in this version. Simulation
tool is specified this time. Some repetitive figures are remove
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