The basic idea in this kind of protocols is that all
nodes in the network agree with a mapping. When nodes are going to send
out location updates, they choose a subset of available nodes. When nodes
need to find some other nodes, they send out location queries to a potentially
di?®erent subset of nodes. Di?®erent protocols should be designd to make sure
that the intersection of two subsets is not empty. These rendezvous nodes act
as location servers where location updates are stored and location queries are
looked up. From the terms of the quorum method, it ensures that a read quorum
can get the current copy of latest location data. Note that the traditional
scheme requires to satisfy the inequality of R+W>n (n is the total number of
nodes), while the rendezvous based method never needs all nodes cooperating
for each data accessing.
Two di?®erent approaches to performing the mapping, hashing-based and
quorum-based, have been proposed [15].
A. Hashing-Based Protocols
In hashing-based protocols, each node chooses its location server via a
hashing function, either in the node identifier space or in the location space.
All location servers form a quorum. The size of quorum is closely related
to hierarchical division and location servers??™ selection. Recall that either in
the traditional read-one/write-all scheme, or one with a majority criterion,
the size R of the read quorum and size W of the write quorum should abide
by R+W> n (n is the total number of nodes), no matter what adjustment is
made between them.
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