Figure 5-5 shows the typical structure of a data packet "manufactured" by an agg~regatio~n
node. Besides the filtered data, each data packet sent from node P will carry four ex-
tra zone parameters: AC_1ocation indicating the coordinates of the agg~regatio~n node P,
Sink_location indicating the coordinates of the sink node R3, and Inner-SemiminorAxis and
Outer-SemiminorAxis indicating the semiminors of the inner and outer ellipses of the de-
sired flooding zone respectively. The field "Warehouse Flag" is used to inform intermediate
nodes whether this packet has ever been processed by a warehouse node. The usage of this
field will be discussed in Section 5.4.4. In addition, based on the fields "Interest (event) De-
scription" and "Other Control Fields", intermediate nodes and sinks can determine whether
one received packet has already been processed, or it needs to assemble those partitioned
packets belonging to the same interest, or to remove the possible redundancy added. The
concrete use of these fields depends on specific applications, which is beyond the scope of
this dissertation.
From the ellipse geometry, we know that when the two endpoints of the major axis
are fixed (that is, AC~location of P and Sink_1ocation of R3), a value of the semiminor
axis can uniquely determine an ellipse. And two different semiminor values (that is, Inner-
SemiminorAxis bl and outer-SemiminorAxis b2) will determine two ellipses as shown in
Fig. 5-4, f(x, y) and g(x, y). Such ellipses can be used to specify multiple flooding zones.
For example, the two ellipses with the same endpoints of the major axis can jointly deter-
mine three non-overlapping flooding zones Zone I between curve 1 and curve 2, Zone II
between curve 2 and curve 3, and Zone III between curve 3 and curve 4. In fact, any two
of the four curves can specify a flooding zone, for example, a bigger zone determined by
curve 1 and curve 3. We already know that, with the two endpoints of the major axis fixed,
the semiminor axis uniquely determines an ellipse. But we need a means to differentiate
5 Here the "inner ellipse" means the ellipse with smaller semiminor axis, while the
"outer ellipse" means the ellipse with bigger semiminor axis.