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  • 1. Layered Video for Incentives in P2P Live Streaming Zhengye Liu Yanming Shen Shivendra Panwar Keith W. Ross Yao Wang Polytechnic University, Brooklyn, NY, USA
  • 2. File Distribution: BitTorrent obtain list of peers trading chunks tracker peer
  • 3. 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
  • 4. 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.
  • 5. BitTorrent: Trading (1) Alice “optimistically unchokes” Bob (2) Alice becomes one of Bob’s top-four providers; Bob reciprocates (3) Bob becomes one of Alice’s top-four providers With higher upload rate, can find better trading partners & get file faster!
  • 6. Basic idea P2P live streaming trade chunks tracker Source of video obtain list of peers peer
  • 7. 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 you’re receiving the video at the full rate?
    • Our main idea:
      • If you upload more, you get better quality.
  • 8. 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
  • 9. 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
  • 10. 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
  • 11. Supplier Side Scheduler
    • Goal: Supply neighbors in proportion to their contributions
    • Measure the download rates, d k from neighbor k
    • Maintain separate FIFO rqst queue for each neighbor
    • Serve neighbor k next with probability:
  • 12. Receiver Side State
    • Request LCs at beginnings of rounds
    • Can request in a window up to B chunks into future
  • 13. 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
  • 14. Receiver Side Scheduler (2)
    • Where to send the request for the LC?
    • Estimate the current delay from each neighbor:
    • where m k is # of outstanding requests, r is video rate, Δ is chunk length
    • Send request to neighbor that will send it first
      • As long as it can come before deadline
  • 15. 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)
  • 16. System Setup
    • Peers
      • Ethernet peer: 1000 kbps; cable peer: 300 kbps;
      • free-rider: 0 kbps
      • Fix ratio of Ethernet peers to cable peers: 3:7; 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
  • 17. Performance Metrics
    • Useful rate received (R)
      • The bits that are useful for video decoding
    • Discontinuity ratio ( α )
      • The percentage of time that a video is undecodable and unplayable
    • Average PSNR (Q)
      • Received video quality
  • 18. 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.
  • 19. Free-Riding
      • Received video quality does not degrade with free-riding
  • 20. Conclusion
    • A decentralized incentive mechanism for video streaming
    • Performance studies show that the scheme can
      • Provide differentiated video quality commensurate with a peer’s contribution
      • Largely prevents free-riders