Layered Video for Incentives in P2P Live Streaming

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Layered Video for Incentives in P2P Live Streaming

• Zhengye Liu
• Yanming Shen
• Shivendra Panwar
• Keith W. Ross
• Yao Wang
• Polytechnic University, Brooklyn, NY, USA

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File Distribution BitTorrent
tracker
obtain list of peers
trading chunks
peer
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BitTorrent Incentive

• Question What is the incentive to provide higher
  upload rate?
• Answer To get file faster
• Implementation Tit-for-tat mechanism. Search for
  trading partners that upload to you at higher
  rates

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BitTorrent Trading

• Alice measures rate she receives bits from each
  neighbor.
• Alice sends chunks to four best neighbors.
• Every 10 seconds, she recalculates rates
  possibly modifies set of four peers.
• Every 30 seconds, she optimistically unchokes
  random peer.

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BitTorrent Trading
(1) Alice optimistically unchokes Bob
(2) Alice becomes one of Bobs top-four
providers Bob reciprocates
(3) Bob becomes one of Alices top-four providers
With higher upload rate, can find better trading
partners get file faster!
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Basic idea P2P live streaming
tracker
trade chunks
Source of video
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Incentives for Live Streaming

• Why upload at all?
• Currently no tit-for-tat mechanism in existing
  deployments
• Is tit-for-tat a sufficient incentive?
• No! Why provide more upload bandwidth if youre
  receiving the video at the full rate?
• Our main idea
• If you upload more, you get better quality.

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Layered Video

• Single layer Video
• All peers receive the same video quality
• Layered video
• A video is encoded into several layers
• More layers introduce better video quality
• Nested dependence between layers
• Higher upload contribution results in better
  received video quality

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Layered Video w/ Tit-for-Tat

• Generate multiple layers, each divided into layer
  chunks (LCs)
• Exchange LCs
• Measure download rates from neighbors
• Reciprocate to neighbors based on their
  contributions

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Supplier Receiver Side Schedulers

• Supplier How to allocate uplink bandwidth to
  neighbors?
• BitTorrent roughly gives each unchoked neighbor
  an equal share.
• Receiver How to maximize the received video
  quality
• Multiple LCs are to be requested

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Supplier Side Scheduler

• Goal Supply neighbors in proportion to their
  contributions
• Measure the download rates, dk from neighbor k
• Maintain separate FIFO rqstqueue for each
  neighbor
• Serve neighbor k next with probability

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Receiver Side State

• Request LCs at beginnings of rounds
• Can request in a window up to B chunks into future

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Receiver Side Scheduler (1)

• Goal Maximize the received video quality
• Which LC should be requested first?
• Assign heuristic importance to each LC, taking
  into account
• Layer index
• Playback deadline
• Rareness
• Request LCs from the highest importance to the
  lowest importance

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Receiver Side Scheduler (2)

• Where to send the request for the LC?
• Estimate the current delay from each neighbor
• where mk is of outstanding requests, r is
  video rate, ?is chunk length
• Send request to neighbor that will send it first
• As long as it can come before deadline

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Performance Study Schemes

• Single layer video without incentives
  (Single-Layer)
• Layered video without incentives (Layered)
• MDC with incentives (MDC-Incent)
• Layered video with incentives (Layered-Incent)

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System Setup

• Peers
• Ethernet peer 1000 kbps cable peer 300 kbps
• free-rider 0 kbps
• Fix ratio of Ethernet peers to cable peers 37
  change percentage of free-riders
• Video
• Foreman video sequence (CIF, 30 frames/sec)
• SVC video codec
• 20 layers, with each layer having a rate of 50
  kbps
• Overlay
• Each peer has 14 to 18 neighbors
• Randomly replace worst neighbor every 30 seconds

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Performance Metrics

• Useful rate received (R)
• The bits that are useful for video decoding
• Discontinuity ratio (a)
• The percentage of time that a video is
  undecodable and unplayable
• Average PSNR (Q)
• Received video quality

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Differentiated Service

• Peers with high upload contributions receive
  better video quality
• Peers with low contributions receive relatively
  low but still acceptable video quality
• Free-riders receive unacceptable video quality.

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Free-Riding

• Received video quality does not degrade with
  free-riding

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Conclusion

• A decentralized incentive mechanism for video
  streaming
• Performance studies show that the scheme can
• Provide differentiated video quality
  commensurate with a peers contribution
• Largely prevents free-riders