This rendezvous
node will provide the matched description about DATA, and forward the
REQ to the sensing node along the route that was traversed by ADV before.
After correctly arriving at the sensing node, the integral data of the event
will be read and forwarded to the soldier along the reverse route that the
REQ traversed. On the whole, the network has been divided conceptually
into di?®erent rows and columns. By using this quorum system, the message
cost for new data dissemination is greatly reduced to O(???n).
Consider the situation, three tanks move into the sensing region of node
A, B, and C, respectively (see Figure 8). Each of these nodes broadcast the
advertisement on detecting tanks in north-south directions (formed by black
nodes), which form three columns with certain thickness. Thus every node in
each column takes a record of the advertisement. Later on, when a soldier
needs to take control of the overall situation on the battlefield, he sends out a
251 Chapter 10 Location Service, Info. Dissemination and Object Tracking
Dan-Dan Liu and Xiao-Hua Jia
request entering the sensor network at node S. This request will be transmitted
in the east-west direction (formed by gray nodes). For example, he may
simply ask: ???Where is the tank, whose ID is 5???? Obviously, there are three different
groups of rendezvous nodes that havevreceived both request and new
advertisement, respectively. They will take a comparison and only the one
that has the matched ADV will respond and continue to forward the REQ
towards the sensing source.
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