1 Dynamic Skyscraper broadcasts for Video-on-demand Derek L. Eager and Mary K. Vernon.

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Dynamic Skyscraper Dynamic Skyscraper broadcasts for Video-on-broadcasts for Video-on-

demanddemand

Derek L. Eager and Mary K. Derek L. Eager and Mary K. VernonVernon

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OutlineOutline

IntroductionIntroduction Skyscraper BroadcastSkyscraper Broadcast Dynamic Scheduling of Skyscraper Dynamic Scheduling of Skyscraper

BroadcastsBroadcasts Experimental ResultsExperimental Results ConclusionConclusion

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IntroductionIntroduction

Divide objects to Two set (hot and Divide objects to Two set (hot and cold)cold) Hot Set : SBHot Set : SB Cold Set : FCFSCold Set : FCFS

The The particular objectsparticular objects (hot set) that (hot set) that are most popular may change with are most popular may change with the time of daythe time of day

DynamicallyDynamically scheduling all objects on scheduling all objects on all available channelsall available channels

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Skyscraper BroadcastsSkyscraper Broadcasts

ConstraintConstraint For any initial unit segment broadcast , For any initial unit segment broadcast ,

there must be a sequence of segments there must be a sequence of segments that the client can receive that will that the client can receive that will support support continuous playback to the continuous playback to the viewerviewer

Clients are required to receive data on Clients are required to receive data on no more than no more than two channelstwo channels simultaneouslysimultaneously

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Skyscraper BroadcastsSkyscraper Broadcasts

ProgressionProgression

we use we use WW to restrict the segments from becoming too to restrict the segments from becoming too large. large.

EXEX：：W= 12W= 12 [ 1 , 2 , 2 , 5 , 5 , 12 , 12 , [ 1 , 2 , 2 , 5 , 5 , 12 , 12 , 12 , 1212 , 12…]…]

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Skyscraper BroadcastsSkyscraper Broadcasts

a

b b

Channel 0

Channel 1

Channel 2

a

b b

a a a

Playback 4 5 61 2 34 5 61 2 3

Case 1 Case 2

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Skyscraper BroadcastsSkyscraper Broadcasts

A

B B

B B

Channel 0

Channel 1

Channel 2

Playback 4 5 61 2 3

Channel 3

AA

AA

A

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Dynamic Scheduling of Dynamic Scheduling of Skyscraper BroadcastsSkyscraper Broadcasts

Skyscraper Transmission ClustersSkyscraper Transmission Clusters

The Basic Dynamic SchemeThe Basic Dynamic Scheme

Temporary Channel StealingTemporary Channel Stealing

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Skyscraper Transmission Skyscraper Transmission ClustersClusters

Non-OverlappingNon-Overlapping transmission cluster transmission cluster SB => K ChannelsSB => K Channels DSB => Transmission ClusterDSB => Transmission Cluster

Start with Start with earliest receptionearliest reception sequencesequence

Each new cluster begins on channel Each new cluster begins on channel 0 precisely 0 precisely W unit W unit after the previous after the previous sequencesequence

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Skyscraper Transmission Skyscraper Transmission ClustersClusters

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The Basic Dynamic SchemeThe Basic Dynamic Scheme

The segment size progression is the The segment size progression is the same as same as Skyscraper broadcastSkyscraper broadcast

All channels be organized into All channels be organized into N N groups of K channels eachgroups of K channels each

A new transmission cluster starts on A new transmission cluster starts on different group different group every (W x T1)/Nevery (W x T1)/N

Request that require a new Request that require a new transmission cluster are scheduled in transmission cluster are scheduled in FCFSFCFS

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The Basic Dynamic SchemeThe Basic Dynamic Scheme

21 11 2

21 1

21 11 2

21 1

2

2

2

2

W=4

N=4?

GROUP 1

GROUP 2

3

3

Channel 0

Channel 1

Channel 0

Channel 1

144* 1 TN

TW

.

.

.

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Temporary Channel StealingTemporary Channel Stealing

OptimizationOptimization of dynamic skyscraper of dynamic skyscraper schemescheme

The requests in an active transmission The requests in an active transmission cluster can only be served early ifcluster can only be served early if 1) the two unit broadcast on channel 1 will 1) the two unit broadcast on channel 1 will

beginbegin at the same time as at the same time as the next unit the next unit segment broadcastsegment broadcast in their group in their group

2) channel 1 in the transmission cluster 2) channel 1 in the transmission cluster that is doing the that is doing the stealing is readystealing is ready

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Temporary Channel StealingTemporary Channel Stealing

1 2

1 2

1

1

Channel 0

Channel 1

Channel 2

Channel 3

2

3

3

2

3

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Transmission ClustersTransmission Clusters

definitiondefinition (1) Use the same segment broadcast (1) Use the same segment broadcast on on

channel Kchannel K (2) Do not use any broadcast periods on (2) Do not use any broadcast periods on

channels 0 through K-1 that are channels 0 through K-1 that are in the in the next transmission clusternext transmission cluster

The diagonally striped segment on The diagonally striped segment on channel 0 are channel 0 are not a member of any not a member of any transmission clustertransmission cluster

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Alternative Segment Size Alternative Segment Size ProgressionsProgressions

additional requirementsadditional requirements The relative segment size The relative segment size on channels 1 on channels 1

and 2 is twoand 2 is two The segment size increases by at most a The segment size increases by at most a

factor offactor of three three at each other step in at each other step in progressionprogression

The transmission cluster of width W on a The transmission cluster of width W on a given channel k>0 given channel k>0 starts just after starts just after channel k-1 broadcastschannel k-1 broadcasts its first segment its first segment of the transmission clusterof the transmission cluster

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Alternative Segment Size Alternative Segment Size ProgressionsProgressions

ExampleExample A(1,2,2,4,4,8,8,16,16…)A(1,2,2,4,4,8,8,16,16…) B(1,2,2,6,6,12,12,24,24…)B(1,2,2,6,6,12,12,24,24…) C(1,2,2,6,6,12,12,36,36)C(1,2,2,6,6,12,12,36,36)

A is the fastest increasing progression that A is the fastest increasing progression that avoids holes avoids holes between transmission between transmission clusters and that also requires clusters and that also requires simultaneous reception on at simultaneous reception on at most two most two channelschannels

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Alternative Segment Size Alternative Segment Size ProgressionsProgressions

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Alternative Segment Size Alternative Segment Size ProgressionsProgressions

The storage requirement for the new The storage requirement for the new progressions is progressions is W – 1W – 1 (occurs W-1 (occurs W-1 time units after the first unit-segment time units after the first unit-segment broadcast)broadcast)

The new segment size progression The new segment size progression also simplify the server disk layout also simplify the server disk layout problemproblem

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Experimental ResultsExperimental Results

We consider systems in which objects We consider systems in which objects are divided two classes are divided two classes (hot set and (hot set and cold set)cold set) Static sky/FCFSStatic sky/FCFS Dynamic sky/FCFSDynamic sky/FCFS Dynamic sky/Dynamic skyDynamic sky/Dynamic sky

SB progression:{SB progression:{1 , 2 , 2 , 5 , 5 , 12 , 12 …1 , 2 , 2 , 5 , 5 , 12 , 12 …}} DSB progression:{1 DSB progression:{1 , , 2 2 , , 2 2 , , 4 4 , , 4 4 , , 8 8 , , 8…)8…)

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Experimental ResultsExperimental Results

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ConclusionConclusion

Performance better than skyscraper broPerformance better than skyscraper broadcast (average client waiting time)adcast (average client waiting time)

The new progression improve dynamic sThe new progression improve dynamic scheduling , simplify disk layout , and all cheduling , simplify disk layout , and all clients with inexpensive settops to receiclients with inexpensive settops to receive the skyscraper broadcastsve the skyscraper broadcasts