So far, there have been several protocols proposed to solve this location service
problem. They can be typically divided into two main categories: proactive
and reactive approaches. They both take ideas from the quorum method.
2.1 Proactive Protocols
In many proactive protocols, one node has to maintain locations of all the
other nodes. They periodically propagate up-to-date location information
throughout the network. The method is like the write-all/read-one scheme in
a distributed database system. Updates take place in all nodes, and whichever
node receives a command can start data retrieval immediately. However, this
will cause high overheads a?®ecting bandwidth utilization, throughput as well
as power usage [12]. It has low scalability. For a large scale wireless sensor
network, or a network composed of nodes with high mobility, large number
of updating interchanges among nodes will consume considerable energy and
even cause many flooding problems.
For example, within the Distance Routing E?®ect Algorithm for Mobility
(DREAM) framework [13], each node maintains a position database that
stores position information about other nodes that are parts of the network.
Locations of nodes will be disseminated throughout the network periodically.
More specific metrics are given to control the frequency of the update to balance
the trade-o?® between overhead in full updating and accurate information
acquisition.
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