It is not Beauty I Demand

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It is not Beauty I Demand George Darley
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Video on Demand

• One video server
• Many video data
• Many clients
• Client want to watch at any time

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Assumptions

• Constant bitrate stream
• Perfect network transport

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Unicast Solution

• One channel per client
• No start-up latency
• No client buffer
• Low client bandwidth
• Large 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 approach
• Scheduling data based on user requests
• Data-centered approach
• Dont care about user
• Just broadcast popular video

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Multicast Solution

• Batching
• Staggered Broadcast

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Staggered Broadcast
Video
C0
C1
C2

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Staggered Broadcast

• 2 hour video
• 5 minutes waiting time
• Number of channels
• 2 x 60 / 5 24
• Required bandwidth

1.5Mbps x 24 36Mbps
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Multicast Solution

• Batching
• Staggered Broadcast
• clients have to wait
• No client buffer
• Low client bandwidth
• Huge server bandwidth

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Multicast Solution

• Batching
• Staggered Broadcast
• Periodic 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 1
Video 2
C0
C1
C2

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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
playback time Ti
i
i1
i1
Doh! Just miss it!
download time Ti1Bv/Bi
Download time for Ti1 needs to be smaller than
Ti for segment i1 to arrive in time.
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Channel Bandwidth
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? 2
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Start-up Latency

• Worst case waiting time T1

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Optimal ?
T1
?
2.5
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Storage Requirements
(TK TK-1)Bv
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Pyramid Broadcast

• Large client bandwidth (?KBv)
• Huge client buffer (7080 Tv)

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Permutation-based Pyramid Broadcast
C0
C1
C2
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Channel Bandwidth
playback time Ti
i
i1
i1
i1
i1
Doh! Just miss it!
download time Ti1Bv/Bi
X
X needs to be smaller than Ti for segment i1 to
arrive in time.
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Channel Bandwidth
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 time
• Can pause and wait

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Storage Requirement
pause
k-1
k-1
k
k
resume
Within time X, better not consume all data in
buffer.
X
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Storage Requirement

• Let buffer content be of size M
• Time to consume the buffer M/Bv

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Comparisons
Scheme Storage Servers BW Clients BW
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 Broadcasting

• Observations
• storage requirement is affected by size of the
  largest chunk
• So, lets limit the size of the largest chunk!

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Pyramid
Skyscraper
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Skyscraper Broadcasting

• Uses 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 Servers BW Clients BW
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 Broadcasting
• Equal segment size, varies bandwidth instead!

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Multicast Solution

• Batching
• Staggered Broadcast
• Periodic Broadcast
• Sending rate playback rate
• May need multiple channels
• Need additional client buffer
• Need to wait

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Multicast Solution

• Batching
• Staggered Broadcast
• Periodic Broadcast
• Patching

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Patching
Time
mcast
unicast
Client Request
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Patching
Patching Window W
Time
mcast
mcast
Client Request
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Grace Patching

• if W lt B
• client buffer videoW .. end
• unicast video0 .. W
• else
• mcast video0 .. 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 Operations

• Pause
• Fast Forward
• Rewind
• Forward Search
• Backward Search
• Slow Mo

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Two Types of Operations

• Continuous (all)
• Discrete Time (pause,ff,rwd)

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Discrete Time

• Easier to implement
• Simple 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
Channel U
Before
Channel U
After
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Pause
Channel U
Before
Channel U
After
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Pause Too Long!
Channel U
Before
Channel U
After
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Channel I
Channel U
Before
Channel I
After
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FF
Channel U
Before
Channel U
After
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FF Too Far!
Channel U
Before
Channel I
After
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RWD
Channel U
Before
Channel U
After
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RWD Too Much!
Channel U
Before
Channel I
After
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Forward Search
Channel U
Before
Channel U
After
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Forward Search Too Far!
Channel U
Before
Channel I
After
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Backward Search
Channel U
Before
Channel U
After
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Backward Search
Channel U
Before
Channel I
After
Prefetched at Reverse Order, at Faster Rate
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Slow Motion
Channel U
Before
Channel U
After
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Slow Motion
Channel U
Before
Channel I
After
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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
Channel I
Before
Channel U
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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
Channel I
Before
Channel U
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Merging Case 2
Channel I
Before
Channel U
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Merging Case 2
Channel I
During
Channel U
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Merging Case 2
Channel I
During
Channel U
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Merging Case 2
After
Channel U
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Summary

• VoD broadcast protocols
• batching
• periodic broadcast
• patching
• Supporting VCR functionalities