3. Receiving and transmitting schedule for nodes at different depths of the tree.
for transmitting a packet. In this case, the packet may be delayed by one or more
epochs.
While the data packets are routed up to the root of the tree, the intermediate nodes
keep aggregating the data. For the example described above, two packets can be aggregated
if they are generated by the sensors that are located in the same room. This
can be easily done by TAG because TAG uses SQL-like query, and the layouts of the
SQL results have the same attributes if they are generated by the same query. Checking
the attribute that is specified in the GROUP BY clause, sensors know whether or
not to aggregate that data in different packets.
Because of in-network aggregation, TAG reduces the required bandwidth and
number of message transmissions to save energy. The in-network aggregation is very
efficient because TAG uses a simple SQL-like query interface which results in the
same layout of the data. These properties make TAG a suitable aggregation service
for low-power, distributed wireless sensor networks.
5 Greedy Aggregation on Directed Diffusion
In [7], the authors propose a more energy efficient aggregation protocol based on
directed diffusion, named Greedy Aggregation. Greedy Aggregation increases the
energy saving by increasing the path sharing among different sources. The number
of aggregations increases because the length of shared path increases, thus achieving
better energy conservation.
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