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2
CB : Consonant Broadcasting
GCB : Grouped Consonant Broadcasting
CB,
m=
1
CB,
m=
2
CB,
m=
4
CB,
m=
16
GCB,
m=
1
GCB,
m=
2
GCB,
m=
4
GCB,
m=
16
1
0
4
b
6
b
8
b
10
b
Network bandwidth (multiples of video bit-rate
b
)
Figure 18.7
Start-up latency versus network bandwidth
where in the second case the first term is the buffer occupancy at time
t
h
j
−
1
+
1
(i.e., when
the last channel is released), the second term and the last term are the amount of media data
consumed and the amount ofmedia data received from time
t
h
j
−
1
+
1
to
t
h
j
+
1
(i.e., (
h
j
−
U
seconds) respectively. The maximum client buffer requirement can then be computed from
H
h
j
−
1
)
·
=
max
{
H
h
j
|∀
j
}
.
18.6.3 Performance Trade-offs
As most Type-II channels in GCB are transmitted at higher than necessary bit-rate, we can
expect it to require more network bandwidth as well as client buffer to achieve the same
latency in CB. We first consider the bandwidth trade-off in Figure 18.7. The results clearly
show that GCB has larger latency than CB at the same network bandwidth setting. However,
the differences decrease significantly when
m
is large. For example, the network bandwidth
required to achieve the same latency of 15 seconds is 7.48
b
and 8.47
b
respectively for CB and
GCB with
m
16.
We also observe similar trade-offs in client buffer requirement as shown in Figure 18.8. As
expected, GCB always requires more client buffer than CB under the same setting. Nevertheless
the differences are again significantly smaller when
m
is large. Another observation is that
variation in the client buffer requirement with respect to network bandwidth is substantially
larger in GCB. Thus, more careful planning is needed to strike a balance between client buffer
requirement and network bandwidth requirement.
In contrast to the two trade-offs, GCB gains in terms of the number of network transmission
channels required. Figure 18.9 plots the number of channels required to achieve a given latency
for CB and GCB. The results clearly show the significant reduction achieved by GCB. For
=
2, and 7.14
b
and 7.23
b
respectively for CB and GCB with
m
=
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