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practice. Thus, for different P2P system implementations to work together, it
is necessary to have such “bridging” mechanisms.
4
3
3
Pastry
1
Chord
2
CAN
4
2
3
1
P2P Proxy
Local Peer
Tapestry
2
4
1
FIGURE 3.7: An internetwork of DHT systems [Fu et al., 2008].
As in a bridge device in a network, the P2P proxy nodes need to support a
dual-protocol stack, as shown in Figure 3.8. Obviously, this requires a higher
capability for such proxy nodes, similar to the situation of a “Super-Node” in
a hierarchical P2P network used in applications such as Skype [Skype, 2009].
To handle the dynamics (i.e., join and leave) of these important proxy nodes,
an election mechanism needs to be used [Fu et al., 2008].
Local Peer
P2P Proxy
P2P Proxy
Local Peer
P2P
App.
P2P
App.
P2P
App.
P2P
App.
P2P
App.
P2P
App.
Pastry
Pastry
Chord
Chord
CAN
CAN
Socket API
FIGURE 3.8: An example protocol stack supporting the implementation of
an internetwork of DHTs [Fu et al., 2008].
Qu et al. [Qu et al., 2009] proposed another interesting P2P internetwork-
ing architecture called truncated pyramid, as shown in Figure 3.9. The essence
of this network architecture is to interconnect different local P2P overlays
(e.g., using Pastry or Chord) by trees. The top overlay, which is the smallest
in size, comprises relative more power nodes (e.g., like Super-Nodes) responsi-
ble for serving as roots of these trees. Less powerful nodes are then designated
roles of internal nodes of the trees. The bulk of other peers, usually forming a
much bigger overlay themselves, are designated as leaves. The communications
among peers in different levels follow the tree paths. For example, when node
1 wants to communicate with node 13, it can either go through node 11 or
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