Incentives - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 114

results also suggest that the proposed scheme, compared with a simple always-
request one, increases the utility and lifetime of every client while reducing
the number of requests sent, at the cost of slightly larger average query delay.
They also compared the performance of the proposed scheme with two popular
schemes that employ client caching. The simulation results show that caching
only benefits clients with high query rates while resulting in both shorter
lifetime and smaller utility in other clients.
5.3.3 Network Access Sharing
Efstathiou and Polyzos [Efstathiou and Polyzos, 2003] studied the problem
of building a federation of wireless networks using a fully autonomous P2P
approach. Specifically, in their system model, there are multiple WLANs, each
of which is considered to be completely autonomous. When a user of one
WLAN enters the domain of a different nearby WLAN, the latter would also
admit the user based on a reciprocity idea. To achieve this, each WLAN is
equipped with a domain agent (DA) which is responsible for managing the
roaming of foreign users. Each DA maintains a counter of tokens, which is
increased when a foreign user is admitted to its WLAN, and is decreased when
a local user travels to a foreign WLAN. The DAs of different WLANs interact
with each other in a pure P2P fashion. Thus, the advantage of this approach
is that there is no need to set up prior pairwise administrative agreements
among different WLANs.
Based on a prototype built using Cisco WLANs, it is found that the pro-
posed P2P-based roaming scheme is e cient.
Kang and Mutka [Kang and Mutka, 2005] considered an interesting prob-
lem in which peers share the access cost of wireless multimedia contents.
Specifically, one peer in the network serves as a proxy which pays a network
server in order to download some multimedia contents in a wireless fashion.
Other peers in the system then share the contents without incurring any cost.
This is achieved by having the proxy broadcast the received multimedia data
to the peers within its transmission range. For other distant peers, rebroad-
casting by the edge peers is employed to serve them. This is illustrated in
Figure 5.19 (left side).
This idea of cost sharing in wireless data access is called CHUM (coop-
erating ad hoc networking to support messaging). A key component in such
sharing is the cost sharing mechanism. In the CHUM system, the peers take
turn, in a round-robin manner, to serve as the proxy. This is illustrated in
Figure 5.19 (right side). It is assumed that the peers have the incentive to fol-
low this round-robin rule based on the reciprocity concept. Simulation results
indicate that 80% of network access cost is saved even with just six peers in
the system.