143,664 research outputs found
Architecture for Cooperative Prefetching in P2P Video-on- Demand System
Most P2P VoD schemes focused on service architectures and overlays
optimization without considering segments rarity and the performance of
prefetching strategies. As a result, they cannot better support VCRoriented
service in heterogeneous environment having clients using free VCR controls.
Despite the remarkable popularity in VoD systems, there exist no prior work
that studies the performance gap between different prefetching strategies. In
this paper, we analyze and understand the performance of different prefetching
strategies. Our analytical characterization brings us not only a better
understanding of several fundamental tradeoffs in prefetching strategies, but
also important insights on the design of P2P VoD system. On the basis of this
analysis, we finally proposed a cooperative prefetching strategy called
"cooching". In this strategy, the requested segments in VCR interactivities are
prefetched into session beforehand using the information collected through
gossips. We evaluate our strategy through extensive simulations. The results
indicate that the proposed strategy outperforms the existing prefetching
mechanisms.Comment: 13 Pages, IJCN
Sensor networks security based on sensitive robots agents. A conceptual model
Multi-agent systems are currently applied to solve complex problems. The
security of networks is an eloquent example of a complex and difficult problem.
A new model-concept Hybrid Sensitive Robot Metaheuristic for Intrusion
Detection is introduced in the current paper. The proposed technique could be
used with machine learning based intrusion detection techniques. The new model
uses the reaction of virtual sensitive robots to different stigmergic variables
in order to keep the tracks of the intruders when securing a sensor network.Comment: 5 page
Majority is not Enough: Bitcoin Mining is Vulnerable
The Bitcoin cryptocurrency records its transactions in a public log called
the blockchain. Its security rests critically on the distributed protocol that
maintains the blockchain, run by participants called miners. Conventional
wisdom asserts that the protocol is incentive-compatible and secure against
colluding minority groups, i.e., it incentivizes miners to follow the protocol
as prescribed.
We show that the Bitcoin protocol is not incentive-compatible. We present an
attack with which colluding miners obtain a revenue larger than their fair
share. This attack can have significant consequences for Bitcoin: Rational
miners will prefer to join the selfish miners, and the colluding group will
increase in size until it becomes a majority. At this point, the Bitcoin system
ceases to be a decentralized currency.
Selfish mining is feasible for any group size of colluding miners. We propose
a practical modification to the Bitcoin protocol that protects against selfish
mining pools that command less than 1/4 of the resources. This threshold is
lower than the wrongly assumed 1/2 bound, but better than the current reality
where a group of any size can compromise the system
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