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60
60
50
50
40
40
30
30
20
20
Variable Service Time
Worst-case Service Time
Resource Increases
10
10
0
0
0
0.5
1
1.5
2
2.5
3
Arrival Rate (requests/second)
Figure 19.15
Performance trade-off for using worst-case service time for dynamic channels
SS-VoD require only six channels. This suggests that SS-VoD will likely outperform TVoD in
practice.
19.4.6 Simplicity versus Performance Trade-off
The admission controller is among the more complex components in the SS-VoD architecture.
One way to simplify the admission controller is to use a constant service time of
T
R
−
δ
seconds for the dynamic channels. As this is the worst-case service time, the admission con-
troller no longer needs to maintain the counter-length tuple
2
and also does not need
to send an
EXTEND
update request to the service node. The trade-off for this simplification is
increased channel requirement as the dynamic channel will be occupied for a time longer than
necessary. Figure 19.15 compares the two cases, showing that using the worst-case service
time of
T
R
−
A
C
,
A
L
}
{
seconds results in resource increases of over 30%. This shows that the more
complex admission procedure is still desirable unless system complexity must be minimized.
2
δ
19.5 Implementation and Benchmarking
We implemented a SS-VoD prototype using off-the-shelf software and hardware. There are
three components in the prototype: service node, admission controller, and video clients. Both
the service node and the admission controller are implemented using the C++ programming
language running on Red Hat Linux 6.2. Two client applications have been developed, one is
implemented using the Java programming language and the Java Media Framework (JMF) 2.1,
while the other is implemented using C++ on the Microsoft Windows platform. Both the
service node and the admission controller are video format independent. The Java-version client
supports MPEG1 streams, while the Windows-version client supports MPEG1, MPEG2, as
well as basicMPEG4 streams.We also implemented the interactive playback controls presented
in Section 19.2, namely pause-resume, slow motion, and seeking.
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