It is first
forwarded along the east and west directions, then bypasses the void area if
any, and finally stops after traversing the outer boundary of the network. On
the contrary, if request is more frequent than detection, we should let the
traversal of REQ be shorter than that of ADV.
Note that there is a tradeo?® between system overhead and data delivery
rate. Decreasing nodes in constructing either quorum will reduce the possibility
of successful intersection. Thickness of each ???column???, ???row???, and
???boundary??? can be increased to reduce delay and increase reliability. In addition,
sensor nodes often detach from the original quorum it resided in without
warning due to mobility or depletion of energy. If those nodes that were supposed
to be in the intersected places are unavailable, the required information
will not be accessible. Therefore, a mechanism is needed to transfer the information
database to other nodes remaining in or moving into the same places,
which substitutes as the new database. Thus nodes in the quorums can transmit
a database with information being picked up by all neighboring nodes
when necessary.
4.3 Other Quorum-Based Protocols
In a recent work, Liu et al [51] proposed a comb-needle query support model,
which forms di?®erent quorum systems (Figure 9). Each sensor node advertises
its DATA message to form a vertical needle with length 2l (write quorum).
A querying node disseminates its REQ to form a vertical comb with gap s
between the teeth (read quorum).
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