Streaming Variable Bit-Rate Media Streams - Scalable Continuous Media Streaming Systems - page 130

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(0.92)

0.9

(0.78)

0.8

0.7

0.6

0.5

0.4

0.3

0.2

(140MB)

0.1

0

0 50 100 150 200 250 300 350 400

Client Buffer Size (MB)

Figure 7.4 Distribution of client buffer requirement for MDR transmission schedules

92% require no more than 140 MB of client buffer. The worst-case client buffer requirement is
394.5 MB. This result is strikingly close to the 20/80 rule, also known as the Pareto's principle
-78% of videos require no more than 20% (100 MB/394.5 MB) of client buffer.
With the trend towards integrating multiple information and entertainment services ranging
from the Web, network gaming, to digital video recorder into a home entertainment center de-
vice, the added buffer requirement can easily be accommodated. Nevertheless, the 20/80 obser-
vation does suggest that the client buffer utilization will be lowmost of the time. We investigate
in the next section an alternative solution that provides better control on the buffer requirement.

7.5 Aggregated Monotonic Decreasing Rate Scheduler
Results from the previous section show that the MDR scheduler can achieve performance com-
parable to Optimal Smoothing, and yet can provide guaranteed video delivery in a mixed-traffic
network. The trade-off, as Section 7.4.3 reveals, is the increased client buffer requirement,
which in a few rare cases reaches close to 400 MB. While even this amount of client buffer can
easily be accommodated in future home entertainment centers with built-in hard disk, there
are still two inefficiencies.
First, our results show that 78% of the video titles in our collection of 274 full-length video
titles require no more than 20% of the worst-case buffer requirement. This suggests that the
client buffer utilization will be low most of the time and most of the reserved buffer space will
be unused.
Second, although video titles with exceedingly large client buffer requirements are rare,
the MDR scheduler cannot prevent such cases as the buffer requirement depends on the indi-
vidual video's bit-rate profile. In other words, the worst-case buffer requirement is, in theory,
unbounded.
To tackle these two deficiencies, we introduce in this section an Aggregated Monotonic
Decreasing Rate (AMDR) scheduler that applies the MDR principle to aggregated network
flows so that relaxed transmission schedules can be used to accommodate those rare video
titles that otherwise require very large buffer requirements.