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
tracker
obtain list
of peers
trading
chunks
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
tracker
obtain list
of peers
peer
trade
chunks
Source
of video

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 Layered 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, dk 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 mk is # of outstanding requests, r is video rate, Δis 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 Video Overlay
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) Discontinuity ratio (α)
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