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An Ef fi cient Implementation of Interactive Video-on-Demand. Steven Carter and Darrell Long University of California, Santa Cruz Jehan-Fran çois Pâris University of Houston. Why Video-on-Demand?. Increased customer convenience Few people enjoy returning video tapes

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an ef cient implementation of interactive video on demand

An Efficient Implementation of Interactive Video-on-Demand

Steven Carter and Darrell Long

University of California, Santa Cruz

Jehan-François Pâris

University of Houston

why video on demand
Why Video-on-Demand?
  • Increased customer convenience
    • Few people enjoy returning video tapes
      • Even fewer people enjoy paying late fees
  • Improved selection of videos
    • Current pay-per-view provides only a small selection of popular videos
  • Savings in time and resources
    • It takes time and fuel to drive to the video rental store
why now
Why Now?
  • Technology becoming available
    • Processors are inexpensive
    • Storage is nearly free ($200 for 40GB)
    • Fast networking is seeing wide deployment
  • Consider the success of Tivo
    • Records live television using MPEG to disk
    • Provides interactive access to recorded programs
why interactive
Why Interactive?
  • It’s hard! It’s more expensive!
    • … but it’s what people expect
  • They won’t give up functionality they have come to expect
    • They’d like to pause to make microwave popcorn
    • They’d like to rewind to see the play again
    • They’d like to be able to fast forward past the boring parts
related research
Related Research
  • Conventional video-on-demand (VoD)
    • Requires one stream per client
  • Patching
    • An independently developed version of stream tapping
  • Batching
    • Group the requests of several clients together
  • Various near video-on-demand (NVoD) schemes
key observation
Key Observation
  • For videos of non-trivial length, several clients will be viewing portions of that video
    • One client watching a 120 minute video and a second client begins watching the same video 10 minutes later
  • The server needs only send data for the non-overlapping portion
    • The potential for savings is enormous
assumptions
Assumptions
  • A set-top-box with:
    • A fast network connection
    • A few gigabytes of local storage
    • A modest processor
  • Keep in mind that set top boxes with these features already exist
our solution
Our Solution
  • Stream Tapping uses multicast to tap in existing video streams
  • Server load is the primary difficult in making VOD a reality
    • Stream Tapping reduces server load by allowing clients to tap into video streams created for other clients
    • Cost per client is dramatically reduced
  • Client waiting time is also reduced
stream types
Stream Types

c

c

C

Partial tap

b

b

Full tap

Stream

B

Complete stream

A

0

2

3

4

Time (since start of complete stream A)

complete streams
Complete Streams
  • Start at a particular position in a video and transmit the remainder of the video
    • For non-interactive Stream Tapping, the starting position is the beginning of the video
  • Used primarily by the first client in a group to view the video
stream types11
Stream Types

c

c

C

Partial tap

b

b

Full tap

Stream

B

Complete stream

A

0

2

3

4

Time (since start of complete stream A)

full tap streams
Full Tap Streams
  • Can be used if the delay () is less than the buffer size ()
  • The full tap stream transmits the video from time 0 to 
  • The complete stream is tapped and written to the buffer while the full tap stream is played
stream types13
Stream Types

c

c

C

Partial tap

b

b

Full tap

Stream

B

Complete stream

A

0

2

3

4

Time (since start of complete stream A)

partial tap streams
Partial Tap Streams
  • Can be used when a complete stream is available but   
    • Note that given current technology,  will be very large
  • The client will tap the complete stream for  units while simultaneously viewing the first  from a partial tap stream
  • Subsequently, partial tap streams of length    are used for the client to catch up to the complete stream
stream types15
Stream Types

c

c

C

Partial tap

b

b

Full tap

Stream

B

Complete stream

A

0

2

3

4

Time (since start of complete stream A)

tapping options
Tapping Options
  • Extra Tapping
    • Allows the client to tap data from any active video stream active, not just the complete stream of the video group
    • Decreases server load by decreasing the length of full tap streams
  • Stream Stacking
    • If the server has streams available, the client can combine them to receive data at rate higher than the nominal rate
    • Allows the server to service stream more quickly, which allows new streams to be scheduled
interactive stream tapping
Interactive Stream Tapping
  • When an interaction begins, Stream Tapping deallocates resources associated with a client
    • If the client was the only one using a stream, then the stream is terminated
  • Stream Tapping determines the resources needed for an interaction, and allocates an interaction stream
    • Note: for rewind, the client’s buffer can be used
  • When the interaction is complete, the client is merged into a video group (tapping existing streams if available)
contingency streams
Contingency Streams
  • These are streams that are held in reserve for interaction
  • The pool of these streams can be managed using high and low watermarks for hysteresis
  • Having such a reserve of streams is essential to avoid blocking
simulation model
Simulation Model
  • Stream Tapping is too complex to model analytically, so we used discrete event simulation
  • The length of the videos was derived from empirical data and a gaussian with mean 102 minutes provided the best fit
  • The popularity of videos was modeled using a Zipf-like distribution, which is the distribution used in most VoD studies
conclusions
Conclusions
  • Stream Tapping has been shown to work well in the interactive environment
  • We have shown that VCR-like controls are possible
    • Previous work has ignored them or only provided course-grained control
  • The use of storage in the STB is an enabling technology
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