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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