Transcript Design_of_an_Interactive_Video-on

Design of an Interactive Videoon-Demand System
Yiu-Wing Leung, Senior Member, IEEE, and
Tony K. C. Chan
IEEE Transactions on multimedia
March 2003
Outline
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Introduction
VOD system architecture
Broadcast delivery schemes
Interactive operations
Design considerations and examples
Conclusions
Introduction
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Client-Server Design
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Maintain a dedicated video stream for each
customer
Use batching policy to server more
concurrent customers
Customers must wait before starting a VOD
session (called access delay)
Introduction
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Broadcasting Design
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Periodic broadcasting
Broadcast multiple streams of the same video
at staggered times periodically
Staggered broadcasting
Similar to periodic, but perform an interactive
operation
VOD system architecture
Video archives
•Connect to an optical fiber
and provide logical channels
•Contain a lot of videos
•Broadcast over multiple
optical channels according to
a broadcast delivery scheme
Proxy
•Logical unit for reception and
transmission
•Receives the video from
optical channel, and transmits
it with video playback rate
VOD system architecture
Scalability
•To add storage and optical
fibers if not sufficient
•VOD warehouse in
distributed site and nearest
customers
Broadcast delivery schemes
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Each video is organized into pages
A video consists of n=9 pages and these
are broadcast over C=3 channels
Two types of broadcast delivery schemes
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Basic broadcast delivery
Interleaved broadcast delivery
Basic broadcast delivery
Video archives broadcast diagram
Basic broadcast delivery
Proxy receives the shaded pages
Basic broadcast delivery
Proxy delivers the retrieved pages to the customer
Basic broadcast delivery
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Buffer size
Proxy retrieves video at the
channel bit rate (50Mbps),
and delivers video at the
video playback rate
(1.5Mbps), so must have
temporary storage
Maximal buffer size
(Rc- Rv) * (Tc / p) = Rv * Tc
Retrieval rate : Rc
Delivery rate : Rv
Duration of a slot : Tc / p
Basic broadcast delivery
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Tuning time
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When proxy has retrieved all the pages from one channel, it tunes
its receiver to another channel.
The maximum permissible tuning time is Tc seconds.
Slot duration
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Depend on Tc, Rc, Rv
Proxy retrieves a page from channel in one slot : (RcTc / p) bits
Proxy delivers this page to the customer in p+1 slots : Rv(p+1)Tc/p
bits
=> Tc / p = Tc*Rv / (Rc – Rv )
Interleaved broadcast delivery
•Divide each page into m minipages, and interleave them in a cycle.
•Page i divided into m minipages, referred to as minipages i1, i2, …,im
Interleaved broadcast delivery
A page (or m minipages) must last for one cycle and
one minislot
Interleaved broadcast delivery
Proxy delivers the retrieved pages to the customer
Interleaved broadcast delivery
Buffer size
(1)
x1 = (Rc – Rv) * (Tc / mp) = Rv * Tc( 1+1/mp-1/p) / m
(2)
y1 = (x1 – Rv * (2Tc / mp) ) = Rv * Tc / m2p
(3)
x2 = (y1 + (Rc – Rv) * (Tc / mp) ) = Rv * Tc( 1+2/mp-1/p) / m
(4)
y2 = (x2 – Rv * (2Tc / mp) ) = 2Rv * Tc / m2p
(5)
X3 = (y2 + (Rc – Rv) * (Tc / mp) ) = RvTc / m
Maximum buffer size is RvTc / m
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Interleaved broadcast delivery
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Tune time
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Proxy retrieved all the minipages of a page from one
channel.
Tuning must be done within p minislots.
Maximum permissible tuning time is (Tc / mp) * p = Tc / m
Minislot duration
Depends on Tc, Rc, Rv, m
 Proxy retrieves m minipages of a page from an optical
channel : RcTc / p bits
 Proxy delievers m minipages to the customer in mp+1
minislots : Rv*(mp+1)Tc / mp
=> Tc / mp = Tc Rv/ (m*Rc – Rv )
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Comparision
Interleaved broadcast scheme support better interactive operations
Interactive operations
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Pause : Tc is smaller, the
approximate is more
similar to the ideal one
 Fast forward :
(1) Play a small portion of video at normal rate
(2) Minipage level is better than page level
Interactive operation
Fast
rewind :
Design consideration
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Design issue
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Optical bandwidth : an optical fiber provide 5 Gbps, so if one
channel needs 50 Mbps, and can provide 100 channel to use.
I/O speed and channel bit rate : we can match the I/O speed of a
disk with the bit rate of an optical channel, so system requires an
small capacity disk.
Video playback rate and duration : Different video can occupy
different number of channels, therefore can accommodate video
with different playback rate (e.g., MPEG-1 and MPEG 2) and
different duration (e.g., 90min and 120min).
Design consideration
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Design parameters
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Cycle duration Tc
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If Tc is larger, a channel can broadcast more pages in a cycle
If Tc is larger, the mean access delay is longer. If service can specify an
acceptable mean access delay T*, then Tc can be chosen to 2T*
Number of minipages per page m
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A page divide into m minipages can reduce each proxy buffer size
The actual tuning time must be equal to or smaller than the maximum
permissible tuning time Tc / m
Each minipage may have to contain at least a certain number of frames
(e.g., contain at least one GOP of nine frame for MPEG)
Design example 1
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Video is compressed by MPEG with nine
frames per GOP.
Because T*=30s, so Tc=2T*=60S
Each video require
[(1.5*106*90*60) / (50*106*60)] = 3
channels. There are 50 video program, so
require two optical fibers
Because tuning time cannot not be larger
than Tc / m, so 10*10-3 ≤ 10/m => m ≤
1000
But since each minipage contain at least
two GOP of frames
Tc ≥ m( 2*9 / 30 ) => m ≤ 100
Buffer size : RvTc / m = 109.9 Kbytes
Design example 2
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Change acceptable mean access delay T*=5s, so Tc=2*5=10
Each video program requires 18 optical channels, so requires ten
optical fibers, where each optical fiber accommodates five video
programs.
Consequently, it provides a better quality (i.e., shorter access
delay and better interactive operation, but use more optical
fibers.
Conclusion
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Adopt both the client-server paradigm and the broadcast
delivery paradigm.
The system can easily be scaled up to serve more concurrent
customer and provide more video .
Provide interactive operations which are approximations of the
ideal ones.
The access delay is small
Each video stream only requires a small buffer size for
temporary storage.