Download - Slides for lecture 1
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P2P Streaming-
Part-1: Native Multicast, End-System Multicast,
and intro to P2P-Streaming
CS 7270Networked Applications &
ServicesLecture-12
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Reading-1
• “Opportunities and Challenges of Peer-to-Peer Internet Video Broadcast” by J. Liu et al.
• Very nicely written tutorial• To appear at IEEE Proceedings this year• Based on (highly influential) ESM project
from Hui Zhang’s group at CMU• Hui’s slides: http://
www.cs.cmu.edu/~hzhang/Talks/ESMPrinceton.pdf
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Reading-2
• “Insights into PPLive: A Measurement Study of a LargeScale P2P IPTV System” by X. Hei et al.
• PPLive: one of the most popular P2Pstreaming systems, mostly used for Chinese TV shows
• Very little known about system architecture
• The paper attempts a measurement-based reverse engineering study
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Basics• PPLive: free P2P-based IPTV• As of January 2006, the PPLive network
provided 200+ channels with 400,000 daily users on average.
• The bit rates of video programs mainly range from 250 Kbps to 400 Kbps with a few channels as high as 800 Kbps.
• The video content is mostly feeds from TV channels in Mandarin.
• The channels are encoded in two video formats: Window Media Video (WMV) or Real Video (RMVB).
• The encoded video content is divided into chunks and distributed to users through the PPLive P2P network.
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System architecture
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• Cached contents can be uploaded to other peers watching the same channel.
• This peer may also upload cached video chunks to multiple peers. • Received video chunks are reassembled in order and buffered in
queue of PPLive TV engine, forming local streaming file in memory.
• When the streaming file length crosses a predefined threshold, the PPLive TV engine launches media player, which downloads video content from local HTTP streaming server.
• After the buffer of the media player fills up to required level, the actual video playback starts.
• When PPLive starts, the PPLive TV engine downloads media content from peers aggressively to minimize playback start-up delay.
• When the media player receives enough content and starts to play the media, streaming process gradually stabilizes.
• The PPLive TV engine streams data to the media player at media playback rate.
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Measurement setup• One residential and one campus PC “watched”
channel CCTV3• The other residential and campus PC
“watched” channel CCTV10 • Each of these four traces lasted about 2 hours. • From the PPLive web site, CCTV3 is a popular
channel with a 5-star popularity grade and CCTV10 is less popular with a 3-star popularity grade.
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Session durations • Signaling versus video sessions• All sessions are TCP based• The median video session is about 20 seconds and about
10% of video sessions last for over 15 minutes or more.
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Video traffic breakdown among sessions
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Start-up delays
• Two types of start-up delay: – the delay from when one channel is selected until
the streaming player pops up; – the delay from when the player pops up until the
playback actually starts.
• The player pop-updelay is in general 10-15 seconds and the player buffering delay is around 10-15 seconds.
• Therefore, the total start-up delay is around 20 30 seconds.
• Nevertheless, some less popular channels have a total start-up delays of up to 2 minutes.
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Upload-download rates
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Upload-download rates (cont)
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Estimating the redundancy ratio• It is possible to download same video blocks more than once
• Excluding TCP/IP headers, determine total streaming payload for the downloaded traffic.
• Utilizing video traffic filtering heuristic rule (packet size > 1200B) extract video traffic.
• Given playback interval and the media playback speed, obtain a rough estimate of the media segment size.
• Compute the redundant traffic by the difference between the total received video traffic and the estimated media segment size.
• Define redundancy ratio as ratio between redundant traffic and estimated media segment size.
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Dynamics of video participants
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Peer arrivals & departures
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Geographic distribution of peers