Incentives - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 117

Let us consider a non-interactive media streaming application in a hybrid
wireless network, which consists of a server and a set of mobile clients, as
shown in Figure 5.20. In this scenario, the primary QoS requirement is to
provide clients with su cient bandwidth in order to achieve uninterrupted
streaming. The effect of delay jitter could be largely compensated by having
enough playback buffers. Thus, we can focus on the amount of bandwidth
from the server to clients.
Each mobile client uses its server interface to access the server, while the
peer interface allows neighboring clients to communicate with one another.
The clients are interested in a piece of media content owned by the server.
We represent the rate of the media content as rkbps and its duration as ts.
Here, the server splits the media content into n stripes using a multiple de-
scription coding scheme. Each stripe is then delivered as a separate stream of
media packets. These n stripes are assumed to be independent and of equal
rate. This arrangement allows heterogeneous clients to adjust their streaming
quality by subscribing to a different number of stripes. The primary QoS re-
quirement is to maintain su cient bandwidth in order to receive those media
packets from the subscribed stripes. Besides satisfying the bandwidth require-
ment, we focus on the energy cost of clients in obtaining the media packets.
Specifically, we treat the QoS requirement as a constraint for optimizing the
energy consumption in the clients.
Ignoring control overheads, the energy cost of receiving the complete media
content, i.e., all n stripes, through the server interface is (Table 5.6 summarizes
the list of symbols and their definitions):

P RX
s
R s ×r×t

E RX
s

= (5.45)

Correspondingly, the energy cost of receiving the complete media content
through the peer interface is:

P RX
p
R p ×r×t

E RX
p

= (5.46)

Tables 5.4 and 5.5 show the technical specifications of typical server and
peer interfaces, respectively. Using these numbers, we have: E RX

s = 103.13J
and E R p = 8.62J. This suggests that it is possible to utilize the peer interface
for energy e cient media streaming in a hybrid wireless network. In particular,
it is interesting to study how heterogeneous clients collaborate to stream the
media content from the server.
To quantify heterogeneity, we represent the type of client x as α x , which
is defined as:

amount of energy client x willing to consume
E RX
s

α x = (5.47)

(n)

Depending on client x's preferences, α x may be any non-negative value.