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On a Unified Architecture forVideo-on-Demand Services

Jack Y. B. Lee

IEEE TRANSACTIONS ON MULTIMEDIA, VOL. 4, NO. 1, MARCH 2002

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OutlineIntroductionUVoD ArchitecturePerformance ModelingNumerical ResultsSimulation ResultsInteractive ControlsConclusions

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Introductiontrue-VoD (TVoD)

Service quality is maximized

near-VoD (NVoD)System cost is minimized

unified VoD (UVoD)Cost-performance tradeoff

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UVoD Architecture (1)

ttm

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UVoD Architecture (2)

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UVoD Architecture (3)

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Admit-via-UnicastArrives at time ttm-1 < t < (tm – δ)

After (t – tm-1)

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Recourse reduction over TVoDAdmit-via-Multicast

As multicast channels is fixed, Admit-via-Multicast users will not result in additional loadIncreasing the admission threshold δ then more user will be admitted to the multicast channels

Admit-via-UnicastSince 0 < (t – tm-1) < (T – δ) ≪ L, unicast channels are occupied for a much shorter duration compared to TVoD

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Performance ModelingLatency (average waiting time)

Admit-via-MulticastAdmit-via-Unicast

Admission ThresholdChannel Partitioning

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Waiting Times (1)Admit-via-Multicast

wM (δ) = δ / 2

Admit-via-UnicastArrival process

λu = ( 1 – δ / TR ) λ

Service timeUniform distribution between 0 < s < TR – δ

Approximation by Allen and Cunneen for G/G/m queue

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Waiting Times (2)

Traffic intensity

Coefficient of variation

Average service time

Server utilization

Erlang-C function

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Admission Threshold

}0,))()((|min{ xTxwxwx RUM

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Channel PartitioningFind the optimum number of multicast channel such that the resultant latency is minimizedTheorem 1: The optimal proportion of available channels to multicast that minimizes the load at the unicast channels is given by

N

M

NLM

LNN opt

M

2

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Numerical ResultsCorresponding Latency Formula

NVoD

The latency is constant at 360(900)s for 10(20) movies

TVoD

MNL

WNVoD

2

2)1(

),( L

N

uNEW C

TVoD

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Admission Threshold verus Queueing Delay

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Channel Partition versus Latency

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Latency Comparison With TVoD and NVoD

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System Capacity and Scalability (1)

%100}0,|max{

}0,|max{

uW

uWG

TVoD

UVoD

λ arrival rate in customers/s

u latency constraint in seconds

WUVoD latency fo UVoD

WTVoD latency fo TVoD

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System Capacity and Scalability (2)

0.1 0.2

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System Capacity and Scalability (3)

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Simulation ResultsEnvironments

Simulation program is developed in C++ using CNCL version 1.10Run 31 days

Model ValidationAdmission Rescheduling

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Model Validation (1)

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Model Validation (2)

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Admission Rescheduling (1)

When Admission Rescheduling?For heavy system loads, a user by Admit-via-Unicast may waiting exceed the time to the next multicast of the requestd movie

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Admission Rescheduling (2)

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Interactive Controls (1)Using Unicast Channels

Break current multicast video stream then restart at some pointTreat interactive controls as new-video requests starting at the middle of a movieCould increase waiting for both and interactive requests

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Interactive Controls (2)Channel Hopping

Client has a buffer large enough to cache TR s

User pause at a movie time Tp

Case1: If resume before buffer overflow, nothing need to be done

Case2:Once buffer is full, stop bufferingLater resume immediately and determine the nearest multicast channel at movie time Tm ≤ Tp

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ConclusionsThis paper propose and analyzes an architecture that unifies the existing TVoD and NVoDThrough admission-threshold and channel partitioning can achieve cost-performance tradeoffResults show large performance gain