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Broker
set
service ID
x
P
rovide
r 1 ask
s $1 fo
r
x
Recursive
lookup for
broker
set
Pro
vid
er 2
as
ks
$2
for
x
FIGURE 5.8: An example of a fully decentralized auction [Hausheer and
Stiller, 2005].
coming requests are prioritized. Simulation results indicate that the proposed
exchange-based mechanisms are effective in terms of file object download time.
Table 5.2 gives a qualitative comparison of different incentive approaches
proposed for P2P file sharing systems. In general, systems that involve pay-
ment would be more di
cult to implement because it is not trivial to design a
global “currency” for use in such systems. Furthermore, security requirement
would be high because the payment could be forged by malicious peers. On
the other hand, exchange-based or reciprocity-based are easier to implement
and hence, are more scalable. The major crux is that there is much less state
information to be kept by each peer. More importantly, the accuracy of such
state information (e.g., reputation) does not need to be absolutely very high.
Thus, we expect that future P2P file sharing would still be based on similar
approaches.
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