AN EVALUATION OF PIECE-PICKING ALGORITHMS FOR LAYERED

CONTENT IN BITTORRENT-BASED PEER-TO-PEER SYSTEMS

ICME 2011

Special Session on Hot Topics in Multimedia Delivery

Michael Eberhard 1Piece-Picking Algorithm Evaluation

Michael Eberhard

Hermann Hellwagner

Christian Timmerer

AAU Klagenfurt

Tibor Szkaliczki Laszlo Szobonya

MTA SZTAKI

OVERVIEW

Introduction to Piece Picking

Algorithm for Layered Piece Picking

Evaluation Results

Single/Multi Layer Comparison

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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.

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PIECE-PICKING BUFFER

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The piece-picking algorithm provides a download strategy for all pieces within the sliding window.

The sliding window contains the pieces that are required for playback in the near future.

PIECE-PICKING SLIDING WINDOW

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PIECE UTILITY CALCULATION

For each piece within the sliding window, the utility is defined as

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𝑼𝒊 𝒋 𝒌 = 𝐝𝐣 × 𝐝𝐩𝐢 𝐣 𝐤(𝐭𝐢 − 𝐭𝐤)𝛂

lj: the layer of the pieceti: the point in time at which the piece is displayedtk: the point in time of the actual decisiondj: the distortion reduction importance of the piecedpijk: the probability to receive the useful piece in time

PIECE MAPPING (1)

GOPs of 64 frames are considered as a unit

2.56 seconds of content are provided commonly for each layer (at 25 fps)

A unit is always entirely downloaded

Only supports layered scalability

For single layer content, ~16 frames of content are mapped to a unit

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PIECE MAPPING (2)

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SIMULATION SETUP

Omnet++/Oversim with new P2P protocol and applications (piece picking algorithms)

Swarm of 100 peers, streaming a one hour video

Peer arrivals and departures are modeled according to a poisson distribution

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MULTI/SINGLE LAYER COMPARISON

Both are encoded with the same constant bitrate and split to fixed-size pieces

Quality for single layer is higher due to SVC overhead

Comparison based on PSNR, as piece size is equal for both encodings (received bitrate is ~equal)

The single layer PSNR for missing pieces is weighted with the PSNR of a black frames

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FULL BANDWIDTH, NO CHURN

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FULL BANDWIDTH, 10% CHURN

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LIMITED BANDWIDTH, 10% CHURN

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MIN/MAX QUALITY/PEER FOR SL

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# Pieces %

4 82.16

3 16.63

2 1.17

1 0.04

0 0

FULL BANDWIDTH, INCREASING CHURN

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FULL BANDWIDTH, 10% CHURN, FRAME LOSS

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CONCLUSION

Layered Video Codecs can be integrated in Bittorrent-based P2P system in a backwards-compatible way

If the bandwidth conditions are not optimal, layered codecs provide a clearly better performance in terms of PSNR

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THANK YOU FOR YOUR ATTENTION!

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