In such
a system each sensor node operates autonomously with no central node of
control in the network. Each node can be a data source (producing data) as
well as a data sink (consuming data). In such an environment, the system is
robust and fault tolerant. It can continue to function properly in the presence
of failures of individual sensor nodes.
A. Quorum-Based Method Description
Specifically, the quorum method is used in conjunction with a negotiation
mechanism that was first introduced in SPIN.
Transmission of ADV message -When a node s has sensed new data, it
broadcasts an ADV to its neighbors in northward and southward directions.
As for the northward direction, the neighbor with the largest y-coordinate
will broadcast the message further to its neighbors. The ADV is propagated
northward hop-by-hop until it reaches the node at the north boundary of the
network. At the same time, the same operation is taken to propagate the ADV
in the southward direction. Figure 3 illustrates the transmission of ADV/REQ,
where s is the source node, t the querying node and u the rendezvous node.
Transmission of REQ message -When a node intends to acquire the
data that it is interested in, it broadcasts a REQ to its neighbors. Similarly
to ADV propagation, the REQ is propagated in both eastward and westward
directions until it reaches the west and east boundaries. Figure 3(a) also illustrates
the propagation of the REQ.
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