Incentives - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 98

the extension is to exploit the spatial distribution of mobile devices to form
clusters. Users in a cluster interact using the DAC mechanism.
Habib and Chuang [Habib and Chuang, 2006] also explored a similar idea
in providing differentiated peer selection to participating peers. Specifically,
a peer has only a limited set of choices (with possibly low media quality) if
it behaves selfishly in the system. The degree of selfishness is reflected by a
score known to other peers. The score is increased if the peer contributes to
other peers, and is decreased if it refuses the requests of other peers. Based
on a practical emulation study using the PROMISE [Hefeeda et al., 2003]
streaming system implemented on top of PlanetLab [PlanetLab, 2006], Habib
and Chuang [Habib and Chuang, 2006] found that the proposed incentive
scheme is effective in enhancing the performance of the system.

5.2.2.2 Multicast One-to-Many Streaming

Ngan et al. considered an application level multicast system for video
streaming. The system is based on SplitStream [Castro et al., 2003a] which in
turn is built on top of Pastry [Rowstron and Druschel, 2001b]. The multicast
system considered critically relies on a payment-based scheme. Specifically,
there are five components:

•Debt Maintenance: When a peer A forwards video streaming data to
a downstream peer B, B owes A a unit of debt.

•Periodic Tree Reconstruction: The multicast tree is reconstructed
periodically in order to avoid prolonged unfair connections among peers.
An unfair connection is one between a well-behaved peer and a selfish
peer.

•Parental Availability: Any new peer can obtain location and address-
ing information about any potential parent peers in the multicast tree.
Thus, the new peer can identify a potential selfish parent if the latter
consistently refuses connection.

•Reciprocal Requests: In the system, any two well-behaved peers are
expected to have an equal chance of being parent or child in any given
multicast tree.

•Ancestor Rating: This is a generalization of the Debt Maintenance
component. Here, debts are also accounted for all ancestors of a peer.
Specifically, all nodes on a path in forwarding data from the source to a
peer are credited or debited in cases where expected data is successfully
received or not, respectively.

Simulation results indicate that a selfish free-rider is effectively penalized
in terms of the amount of video streaming data received.
Chu and Zhang [hua Chu and Zhang, 2004] also considered a multicast-
based streaming environment. The streaming process is synchronous and is