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Resource constraints are a concern for any distributed system in which end-user
devices are called upon to contribute to the whole of the system. One technique
used by the P2P community is to balance system load by creating a hierarchical
network where resource-plentiful nodes are promoted to ultra or super status
[6,14]. Wireless network, for example, supports two types of peers: ultrapeers and
leaves. Ultrapeers are full participants in the network and must relay messages,
perform searches, and cache information. Leaves merely consume the services
of the network through ultrapeers. When a node joins the Gnutella network, it
is initially designated as a leaf. If a node has the appropriate bandwidth and
connectivity characteristics, it will try to promote itself to ultrapeer status after
it has been online for at least 1 hour.
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