it is not beauty i demand – george darley
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It is not Beauty I Demand – George Darley
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Video on Demand
One video serverMany video dataMany clientsClient want to watch at any time
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Assumptions
Constant bitrate streamPerfect network transport
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Unicast Solution
One channel per clientNo start-up latencyNo client bufferLow client bandwidthLarge server bandwidth Not scalable
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Multicast Solution
Batching aggregate client requests serve using multicast clients have to wait No client buffer Low client bandwidth
“Scheduling Policies for an On-Demand Video Server with
Batching”
Dan, Sitaram, Shahabuddin, IBM
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Multicast Solution
User-centered approachScheduling data based on user
requests
Data-centered approachDon’t care about userJust broadcast popular video
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Multicast Solution
BatchingStaggered Broadcast
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Staggered Broadcast
Video
C0
C1
C2
:
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Staggered Broadcast
2 hour video5 minutes waiting timeNumber of channels =
2 x 60 / 5 = 24
Required bandwidth =
1.5Mbps x 24 = 36Mbps
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Multicast Solution
BatchingStaggered Broadcast
clients have to waitNo client bufferLow client bandwidthHuge server bandwidth
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Multicast Solution
BatchingStaggered BroadcastPeriodic Broadcast
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Periodic Broadcast
Video
C0
C1
C2
:
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Pyramid Broadcast
Video
C0
C1
C2
:
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Pyramid Broadcast
Video 2
C0
C1
C2
:
Video 1
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Pyramid Broadcast
Video
C0
C1
C2
:
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Analysis of Pyramid Broadcast
Notations B : Total available bandwidth Bv : Bandwidth of video
Tv : Total length of each video K : Number of segments per video Ti : Length of segment i : Factor in geometric series
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Channel Bandwidth
i
i+1 i+1
playback time = Ti
download time = Ti+1Bv/Bi
Download time for Ti+1 needs to be smaller than Ti for segment i+1 to arrive in time.
D’oh!Just miss it!
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Channel Bandwidth
since
1
11
1
1
vi
iivi
i
vii
KBKBB
TTBB
B
BTT
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= 2
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Start-up Latency
Worst case waiting time = T1
1
)1(
1
)1( 11
vB
B
K
v
TTT
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Optimal
2.5
T1
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Storage Requirements
~ (TK + TK-1)Bv
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Pyramid Broadcast
Large client bandwidth (KBv)
Huge client buffer (70–80% Tv)
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Permutation-based Pyramid Broadcast
C0
C1
C2
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Channel Bandwidth
i
i+1 i+1
playback time = Ti
download time = Ti+1Bv/Bi
X needs to be smaller than Ti for segment i+1 to arrive in time.
D’oh!Just miss it!
i+1 i+1
X
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Channel Bandwidth
)(
, and since
11
1
1
1
v
iii
i
vi
i
vii
KBpB
KBpBTT
pB
BT
B
BTT
p : number of sub-channels per segments
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Client Latency
Just T1/p
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Storage Requirement
One channel at a timeCan pause and wait
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Storage Requirement
k-1
k
k
k-1
pause
resume
X
Within time X, betternot consume all data in buffer.
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Storage Requirement
Let buffer content be of size MTime to consume the buffer = M/Bv
pα
)BT(T M
p
p)B(α B
B
M
B
BT
B
BT
p
vK-K
vi
vi
vi
i
vi
1
1
know we
1
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Comparisons
Scheme Storage Server’sBW
Client’sBW
Pyramid 70% KBv 4-5 Bv
Pyramid++ 20% (+p)KBv 2-3 Bv
Carter, Long and Paris “Video on Demand Broadcasting Protocols”
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Pyramid Broadcasting
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Skyscraper BroadcastingObservations:
storage requirement is affected by size of the largest chunk
So, let’s limit the size of the largest chunk!
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Pyramid Skyscraper
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Skyscraper BroadcastingUses series
1 2 2 5 5 12 12 25 25 52 52 … W W W
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Skyscraper Example
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Skyscraper Example
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Comparisons
Scheme Storage Server’sBW
Client’sBW
Pyramid 70% KBv 4-5 Bv
Pyramid++ 20% (+p)KBv 2-3 Bv
Skyscraper 10% KBv 1-2 Bv
Carter, Long and Paris “Video on Demand Broadcasting Protocols”
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Other schemes
Pagoda Broadcasting 1 3 5 15 25 75 125 …
Harmonic BroadcastingEqual segment size, varies bandwidth instead!
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Multicast Solution
BatchingStaggered BroadcastPeriodic Broadcast
Sending rate ≥ playback rateMay need multiple channelsNeed additional client bufferNeed to wait
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Multicast Solution
BatchingStaggered BroadcastPeriodic BroadcastPatching
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Patching
Time
Client Request
mcast
unicast
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Patching
Time
Client Request
Patching Window: W
mcast
mcast
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Grace Patching
if W < Bclient buffer video[W .. end]unicast video[0 .. W]
elsemcast video[0 .. end]
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Example
30 minutes video 15 minutes buffer One request per minute
465.271.225
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Example
What if patching window = 5 min?
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Supporting VCR OperationsPauseFast ForwardRewindForward SearchBackward SearchSlow Mo
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Two Types of OperationsContinuous (all)Discrete Time (pause,ff,rwd)
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Discrete Time
Easier to implementSimple in staggered broadcasting
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Continuous Time
Requires buffering of future frames and previous frames
Abram-Profeta and K.G. Shin, "Providing Unrestricted VCR Functions in Multicast Video-on-Demand Servers,"
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Normal Playback
Before
After
Buffer
Playout Point
Oldest Frame Newest Frame
Channel U
Channel U
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Pause
Before
AfterChannel U
Channel U
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Pause Too Long!
Before
AfterChannel U
Channel U
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Channel I
Before
AfterChannel I
Channel U
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FF
Before
AfterChannel U
Channel U
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FF Too Far!
Before
AfterChannel I
Channel U
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RWD
Before
AfterChannel U
Channel U
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RWD Too Much!
Before
AfterChannel I
Channel U
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Forward Search
Before
AfterChannel U
Channel U
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Forward Search Too Far!Before
AfterChannel I
Channel U
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Backward Search
Before
AfterChannel U
Channel U
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Backward Search
Before
AfterChannel I
Channel U
Prefetched at Reverse Order, at Faster Rate
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Slow Motion
Before
AfterChannel U
Channel U
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Slow Motion
Before
AfterChannel I
Channel U
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The Aftermath
When playback resumes, what to do with Channel I?
Answer: Merge back with Channel U
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Merging Operation
Find a target channel whose play point is ”not too far” ahead
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Merging: Case 1
Before
Channel U
Channel I
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Merging: Case 1
During
Channel U
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Merging: Case 1
After
Channel U
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Merging: Case 2
Before
Channel U
Channel I
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Merging: Case 2
Before
Channel U
Channel I
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Merging: Case 2
During
Channel U
Channel I
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Merging: Case 2
During
Channel U
Channel I
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Merging: Case 2
After
Channel U
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Summary
VoD broadcast protocolsbatchingperiodic broadcastpatching
Supporting VCR functionalities
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