1 layered video for incentives in p2p live streaming zhengye liu yanming shen shivendra panwar keith...
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Layered Video for Incentives in P2P Live Streaming
Zhengye LiuYanming Shen
Shivendra PanwarKeith W. Ross
Yao Wang
Polytechnic University, Brooklyn, NY, USA
File Distribution: BitTorrent
obtain listof peers
trading chunks
tracker
peer
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
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.
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!
obtain listof peers
trade chunks
tracker
peer
Basic idea P2P live streaming
Sourceof video
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.
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
L4
L3
L2
L1
L2
L1
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
LC11
LC21
LC31
LC12
LC22
LC32
LC13
LC23
LC33
LC14
LC24
LC34Layer 3
Layer 2
Layer 1
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
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:
Requests queue
...
Receiver 1 Receiver 2 Receiver K
i i
kk d
dp
Receiver Side State
• Request LCs at beginnings of rounds• Can request in a window up to B
chunks into future
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
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
kk d
rm
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)
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
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
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.
Free-Riding
Received video quality does not degrade with free-riding
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