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B for distribution to A, C, and F. Essentially, using a single tree might be a
suboptimal arrangement.
Thus, it is proposed [Gu et al., 2008] that a “decoupled” approach is used,
as illustrated in Figure 2.2(d). Here, we have two logical trees—one for mixing
and the other for distribution. It is important to note that the constituents
of these two trees are designated from the set of participants (i.e., A, B,
C, D, E, and F). Indeed, in this approach, a node needs to overload itself
to play potentially two to three roles (i.e., as a participant, a mixer, and a
distributor). Now, when nodes A and B speak simultaneously, their packets
get transmitted along the mixing tree. The final mixed outcome will then
be passed to the distribution tree, from which all the participants get the
packets. The key advantage of this approach is that based on the knowledge
of the system capabilities (e.g., bandwidth) of the participants, two optimal
trees can be determined to support the conferencing operations.
A
A
B
B
C
C
F
F
D
E
D
E
(a) multiple multicasting
(b) multiple multicasting
D
E
F
A
B
C
M
1
M
2
A
B
C
M
3
D
1
D
2
D
3
F
D
E
D
E
F
A
B
C
(c) multiple multicasting
(d) multiple multicasting
FIGURE 2.2: Approaches for mixing and distributing VoIP data in a mul-
tiparty scenario [Gu et al., 2008].
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