34,922 research outputs found
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
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
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
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A systematic review of lesbian, gay, bisexual and transgender health in the West Midlands region of the UK compared to published UK research
It is estimated that approximately 3-8% of the UK population identify as lesbian, gay, bisexual or trans (LGBT). Until now, most health research on gay and bisexual men has been around HIV, AIDS and sexually transmitted diseases and for trans people has been on the transitioning process only. However, it has been apparent to the LGBT community that that there are a wide variety of other physical and mental health issues that are also important and that the proportion of gay and bisexual men who have HIV/AIDS is relatively small. Very little general LGBT health research has been published so far and there are very few health services that specifically address the general health concerns of the LGBT community. This systematic review presents all available research conducted in the West Midlands on LGBT health since 2000. Local health research is compared to UK national, peer reviewed and published LGBT health research in order to determine whether the local results are unusual compared to national LGBT data, and to routinely collected data on the UK population, where appropriate, in order to determine whether and where the LGBT population differ from the general population. Only UK research has been included because there was no previous UK specific
systematic review so it was unclear how generalisable foreign research would be to the UK
Students with Asperger’s Syndrome transitioning to postsecondary education: What are the common issues?
This study explored the common issues that emerged during a peer coaching intervention program for students with Asperger\u27s Syndrome (AS). Nineteen undergraduate college students with AS (4 females, 15 males, age range: 18 - 23 years) participated in the Spectrum Support Pilot (i.e., peer coaching intervention program), and seven second year graduate students (7 females, age range: 23 – 26 years) within the School Psychology program at the same university served as peer coaches. Peer coaches wrote DAP (Description, Assessment, Plan) notes, which provided qualitative information about each meeting with their students. DAP notes were coded for common themes; the following seven themes emerged from the notes, indicating that these were areas of difficulties for students with AS: (a) organization and time management; (b) emotional control and anxiety; (c) social interaction and communication; (d) behavior; (e) adaptive and independent living; (f) self-advocacy; and (g) flexibility and adaptability. Exploring common issues that students with AS face in postsecondary education can provide postsecondary institutions with a better understanding of these students\u27 unique difficulties so that they can better support them
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