This document evaluates piece-picking algorithms for layered content streaming in BitTorrent-based peer-to-peer networks. It introduces a piece-picking algorithm that decides which pieces to download over time based on layer, display time, and probability of receiving pieces. The algorithm is evaluated through simulations of single and multi-layer encodings under different bandwidth and churn conditions. The results show that layered video codecs can be integrated into BitTorrent P2P systems and provide better performance than single-layer encodings when bandwidth is limited or churn is present.

1. An Evaluation of Piece-Picking Algorithms for LayeredContent in Bittorrent-based Peer-To-Peer Systems ICME 2011 Special Session on Hot Topics in Multimedia Delivery Michael Eberhard 1 Piece-Picking Algorithm Evaluation Michael Eberhard Hermann Hellwagner Christian Timmerer AAU Klagenfurt TiborSzkaliczki Laszlo Szobonya MTA SZTAKI

2. Overview Introduction to PiecePicking AlgorithmforLayeredPiecePicking Evaluation Results Single/Multi LayerComparison Michael Eberhard Piece-Picking Algorithm Evaluation 2

3. Piece-Picking in P2P Networks When streaming layered videos in a P2P network, the piece-picking algorithm needs to decide which piece to download at which point in time. The main goal is to provide the best possible quality with the available bandwidth while ensuring continuous playback and minimizing changes in quality. Michael Eberhard Piece-Picking Algorithm Evaluation 3

6. Piece Utility Calculation For each piece within the sliding window, the utility is defined as Michael Eberhard Piece-Picking Algorithm Evaluation 6 lj: thelayer of thepiece ti: the point in time at whichthepieceisdisplayed tk: the point in time of the actualdecision dj: thedistortionreductionimportanceof thepiece dpijk: theprobability to receivetheusefulpiece in time

7. PieceMapping (1) GOPs of 64 framesareconsidered as a unit 2.56 seconds of contentareprovidedcommonlyforeachlayer (at 25 fps) A unitisalwaysentirelydownloaded Onlysupportslayeredscalability For singlelayercontent, ~16 frames of contentaremapped to a unit Michael Eberhard Piece-Picking Algorithm Evaluation 7

8. PieceMapping (2) Michael Eberhard Piece-Picking Algorithm Evaluation 8

9. Simulation Setup Omnet++/Oversimwithnew P2P protocol and applications (piecepickingalgorithms) Swarm of 100 peers, streaming a onehourvideo Peer arrivals and departuresaremodeledaccording to a poissondistribution Michael Eberhard Piece-Picking Algorithm Evaluation 9

10. Multi/Single LayerComparison Bothareencodedwiththesameconstantbitrate and split to fixed-sizepieces Qualityforsinglelayerishigherdue to SVC overhead Comparisonbased on PSNR, as piecesizeisequalforbothencodings (receivedbitrateis ~equal) Thesinglelayer PSNR formissingpiecesisweightedwiththe PSNR of a blackframes Michael Eberhard Piece-Picking Algorithm Evaluation 10

11. Full Bandwidth, No Churn Michael Eberhard Piece-Picking Algorithm Evaluation 11

12. Full Bandwidth, 10% Churn Michael Eberhard Piece-Picking Algorithm Evaluation 12

13. LimitedBandwidth, 10% Churn Michael Eberhard Piece-Picking Algorithm Evaluation 13

14. Min/Max Quality/Peer for SL Michael Eberhard Piece-Picking Algorithm Evaluation 14

15. Full Bandwidth, IncreasingChurn Michael Eberhard Piece-Picking Algorithm Evaluation 15

16. Full Bandwidth, 10% Churn, Frame Loss Michael Eberhard Piece-Picking Algorithm Evaluation 16

17. Conclusion Layered Video Codecscanbeintegrated in Bittorrent-based P2P system in a backwards-compatible way Ifthebandwidthconditionsare not optimal, layeredcodecsprovide a clearlybetterperformance in terms of PSNR Michael Eberhard Piece-Picking Algorithm Evaluation 17

18. Thankyouforyour Attention! Michael Eberhard Piece-Picking Algorithm Evaluation 18