The most important fact is that when
the row and column intersect, some nodes (in the case of Figure 3(a), node u
and two other nodes in the small square) must have received both ADV and
REQ, which are rendezvous nodes.
Transmission of DATA message -The first rendezvous, in which a pair
of ADV and REQ matches, continues to send the REQ to the source node
along the route where the matched ADV was transmitted. Upon receiving
the REQ, the source node transmits DATA message to the querying node
along the same route as the REQ. This can avoid extra routing for DATA
244
messages, which could save significant routing overhead in sensor networks.
An alternative method used after ADV and REQ are matched is geometric
routing, such as Greedy Perimeter Stateless Routing (GPSR) [29], Geometric
Adaptive Face Routing (GOAFR) [30], or Greedy-Face-Greedy (GFG) [31].
Such geometric routing will help build the shortest path between source node
and querying node.
t
u
ADV
REQ
s
(a) (b) (c)
t
u
s
t
u
s
REQ DATA
Fig. 3. Illustration of the quorum-based information dissemination.
Note that there is no need of ordering ADV and REQ for the matched
data. Arrived messages will be stored for future matching until expiration
time is reached.
In this scheme, the quorum system is constructed in a similar way as it
is applied to location service. The di?®erence is that the negotiation message,
ADV, is forwarded to the write quorum, while new data only updates in the
sensing node.
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