Incentives - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 77

ent applications. In a file sharing application, the most important metrics are
downloading time and the integrity of the received files. In a media streaming
application, the more crucial performance parameters are the various play-
back quality metrics such as jitter, frame-rate, resolution, etc. Furthermore,
the incentive techniques surveyed in this chapter subsume the underlying P2P
network topology. Specifically, in most proposed systems, the communication
message exchange mechanism is not explicitly modeled.
Currently, the majority of P2P systems are implemented over the Inter-
net. However, wireless P2P systems are also proliferating. While most of the
incentive techniques designed for a wired environment could be applicable in
a wireless system, the wireless connectivity is by itself an important bootstrap
sharing problem. Indeed, on the Internet, users seldom pay attention to the
connectivity issue because a user can be reached (or can reach) any other In-
ternet user without noticeable effort. The only concern about communication
is the uploading or downloading bandwidth consumption. In a wireless envi-
ronment, however, the mere action of sending a request message from a client
peer to a server peer would probably need several intermediate peers to help
do the message forwarding because the server and client peers may be out of
each other's transmission range. Consequently, incentives have to be provided
to encourage such forwarding actions.
In this chapter, we survey state-of-the-art solutions proposed for tack-
ling the incentive issues in various different P2P resource sharing systems.
In Section 5.2, we describe approaches designed for providing incentives in
Internet-based P2P networks. We discuss both file sharing and media stream-
ing applications. In Section 5.3, we describe solutions suggested for wireless
P2P systems. We then provide some of our interpretations and suggestions in
Section 5.4. We summarize this chapter by providing some remarks in Sec-
tion 5.6.
5.2 Incentive Issues in P2P Systems on the Internet
5.2.1 File Sharing Systems
In a file sharing system, users would like to retrieve files from other users,
and would expect other users to do the same. Thus, each user would need to
expend two different forms of resource:
•Storage: Each user has to set aside some storage space to keep files that
may be needed by other users, even though such files may not be useful
to the user itself.
•Bandwidth: Each user has to devote some of its outbound bandwidth
for uploading requested files to other users.