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balancing cluster) of regular peers to share the workload. Thus, the topol-
ogy control actions of this network architecture are mainly related to load
balancing concerns.
Load Balancing
Cluster (LBC)
Regular Node
Regular Node
Super Node
Regular Node
Regular Node
Load Balancing
Cluster (LBC)
Load Balancing
Cluster (LBC)
Regular Node
DHT Ring
Super Node
Super Node
Regular Node
Regular Node
Regular Node
Super Node
Load Balancing
Cluster (LBC)
Regular Node
Regular Node
FIGURE 4.4: A semi-structured P2P network architecture [Ohnishi et al.,
2007].
Specifically, Ohnishi et al. [Ohnishi et al., 2007] considers the following
two kinds of load-balanced topology control actions, based on periodic load
information exchange among the Super Nodes.
1. A Super Node transfers a regular node in its LBC to another Super
Node.
2. A Super Node elevates a regular node in its LBC to be a new Super
Node, thereby creating a new LBC.
To initiate one of these topology control actions, each Super Node i pe-
riodically checks its average number of object requests (e.g., file searches),
denoted as A
i
over a certain time period. Two Super Nodes, i and j, can then
compare their respective load levels using the ratio A
i
/A
j
. Specifically, if the
ratio is greater than a certain pre-defined threshold, the first kind of transfer
from node i to j takes place. On the other hand, if the ratio stays within a
certain pre-defined range for all j but the number of regular nodes in i's LBC
gets too large, then the second kind of transfer takes place. Here, the number
of nodes in each LBC (including the Super Node itself) is governed by:
(1−β)N
R
N
S
n
r
= βN
R
F
i
+
(4.3)
where N
R
is the total number of regular nodes in the system, N
S
is the total
number of Super Nodes, F
i
represents the sum of all ratios at which a request
is made for all the objects (e.g., files) included in LBC
i
, and β is a system
parameter (set to be 1 in [Ohnishi et al., 2007]).
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