6 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
Spatial Fluid Limits for Stochastic Mobile Networks
We consider Markov models of large-scale networks where nodes are
characterized by their local behavior and by a mobility model over a
two-dimensional lattice. By assuming random walk, we prove convergence to a
system of partial differential equations (PDEs) whose size depends neither on
the lattice size nor on the population of nodes. This provides a macroscopic
view of the model which approximates discrete stochastic movements with
continuous deterministic diffusions. We illustrate the practical applicability
of this result by modeling a network of mobile nodes with on/off behavior
performing file transfers with connectivity to 802.11 access points. By means
of an empirical validation against discrete-event simulation we show high
quality of the PDE approximation even for low populations and coarse lattices.
In addition, we confirm the computational advantage in using the PDE limit over
a traditional ordinary differential equation limit where the lattice is modeled
discretely, yielding speed-ups of up to two orders of magnitude