Conclusions - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 171

P2P system is sustainable, which requires a certain minimum level of cooper-
ation, some incentive schemes have to be in place. That is why, for example,
BitTorrent, being the currently most popular file sharing scheme, also has a
simple yet effective incentive mechanism (i.e., the tit-for-tat strategy). How-
ever, for many other existing P2P systems, there is generally a lack of proper
incentive schemes, despite that there are many approaches proposed in the
research community.
Similarly, despite that many trust management schemes have been sug-
gested by researchers, they still do not find their way into real life implemen-
tations. Trust among peers is still largely based on the “real life trust” among
the physical users behind the peers. That is, if a user has interacted with an-
other user for quite some time, there will be a certain level of trust established
between them, and thus, such trust is also manifested between the two peers in
the P2P network. Autonomous trust management by the peer client programs
is still far from a reality. This is true even for some seemingly successful P2P
information sharing (or sometimes called static crowd sourcing) applications
such as Wikipedia [Wikipedia, 2011] in that the “trust” associated with each
information item shared is largely based on o ine peer reviewing on the part
of the human users.
With a lack of systematic and autonomic trust management, security issues
are even more important because a peer might be sharing data with another
peer with distrust, which may even be malicious. However, simply put, security
is by and large a void in existing P2P systems. People could easily get bogus
file data which might even contain some malware or virus. Similar to the
situation of trust, security is still based on physical user's judgment—the user
manually decides which “torrent” to join to download a file, manually observes
whether some links would lead to some phishing sites, etc.
Even when we consider a highly successful P2P streaming system like
PPLive in Chapters 5 to 7, there are voids in key aspects such as incentive,
trust, and security. Thus, these areas are fertile grounds for high impact re-
search.
8.2 Peer into the Future
“Peering” into the future, we would see P2P applications not just allowing
us to share information and processing power but also some more fundamental
resources, such as energy in our mobile devices, network bandwidth, security
keys, etc. In terms of sharing, different P2P applications could be merged
in the sense that getting some video data from a peer would mean giving
some file data to it as exchange. That is, in the future, the currently more or
less homogeneous “trade” (or barter) would become a wholesale “economy”
in which peers trade different kinds of “goods.” To make this happen, we