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CS 414 - Spring 2008
CS 414 – Multimedia Systems Design Lecture 40 – P2P Media Streaming
William Conner
Spring 2008
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Outline
Background IP Multicast Content delivery networks P2P media streaming design
Tree-basedMesh-based
Case study: PPLive
CS 414 - Spring 2008
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Reading
“Opportunities and Challenges of Peer-to-Peer Internet Video Broadcast” by Liu et al. (Required)
“Insights into PPLive: A Measurement Study of a Large-Scale P2P IPTV System” by Hei et al. (Recommended)
“Mapping the PPLive Network: Studying the Impacts of Media Streaming on P2P Overlays” by Vu et al. (Recommended)
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Acknowledgements
Some lecture material borrowed from the following sourcesSanjay Rao’s lecture on P2P multicast in his
ECE 695B course at Purdue“Insights into PPLive: A Measurement Study
of a Large-Scale P2P IPTV System” by Hei et al.
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Background
Large-scale video broadcast over Internet Real-time video streaming Need to support large numbers of viewers
AOL Live 8 broadcast peaked at 175,000 (July 2005) CBS NCAA broadcast peaked at 268,000 (March 2006)
Very high data rate TV quality video encoded with MPEG-4 would require 1.5
Tbps aggregate capacity for 100 million viewers NFL Superbowl 2007 had 93 million viewers in the U.S.
(Nielsen Media Research)
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Possible Solutions
Single server IP multicast Content delivery networks (CDNs) Application end points (pure P2P)
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Single Server
Application-layer solution Single media server unicasts to all clients
Needs very high capacity to serve large number of clients CPU Main memory Bandwidth
Impractical for millions of simultaneous viewers
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Single Server
P
CC
C
CC C
C
C
C
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IP Multicast
Network-layer solution Routers responsible for multicasting
Efficient bandwidth usage Requires per-group state in routers
Scalability concern Violates end-to-end design principle
Slow deployment IP multicast is often disabled in routers
Difficult to support higher layer functionality
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IP Multicast
“Smart Network”
Berkeley
Gatech Stanford
Per-group Router State
Source:
Purdue
Source: Sanjay Rao’s lecture from Purdue
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Overlay Network
Consists of application-layer links Application-layer link is logical link consisting of
one or more links in underlying network Used by both CDNs and pure P2P systems
R1 R2A B
R3C D
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Content Delivery Networks
Strategically located replicas unicast content to nearby clients Reduces burden on primary server Improves perceived performance at client
Akamai CDN is the largest Reports peak aggregate capacity of 200 Gbps Not enough for 1.5 Tbps requirement for 100 million
simultaneous viewers Limelight CDN served YouTube content
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Content Delivery Networks
P
R1
R2
R3
CC
C
CC C
C
C
C
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P2P Applications
Many P2P applications since the 1990sFile sharing
Napster, Gnutella, KaZaa, BitTorrent
Internet telephony Skype
Internet television PPLive, CoolStreaming
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Why P2P?
Every node is both a server and clientEasier to deploy applications at endpointsNo need to build and maintain expensive
infrastructurePotential for both performance improvement
and additional robustnessAdditional clients create additional servers for
scalability
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Purdue
Stan1
Stan2
Berk2
Overlay Tree
Stanford
Berkeley
Dumb Network
Gatech
Gatech
Berk1
Stan1
Stan2
Berk1
Berk2
Source:
Purdue
P2P Multicast
Source: Sanjay Rao’s lecture from Purdue
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P2P Multicast
Tree-based Parent-child relationships Push-based Uplink bandwidth not utilized at leaves
Data can be divided and disseminated along multiple trees (e.g., SplitStream)
Must be repaired and maintained to avoid interruptions
Example: End System Multicast (ESM)
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P2P Multicast
Mesh-basedData-drivenPull-basedPeriodically exchange data availability with
random partners and retrieve new dataUnlike BitTorrent, must consider real-time
constraintsExample: CoolStreaming
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Overlay Performance
Even a well-designed overlay cannot be as efficient as IP Mulitcast But performance penalty can be kept low Trade-off some performance for other benefits
Increased Delay
Dumb Network
GatechDuplicate Packets:
Bandwidth Wastage
Stanford
Berkeley
Source: Sanjay Rao’s lecture from Purdue
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Case Study: PPLive
Very popular P2P IPTV applicationFree for viewersOver 100,000 simultaneous viewers and
400,00 viewers dailyOver 200+ channelsWindows Media Video and Real Video format
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Case Study: PPLive
Gossip-based protocolsPeer managementChannel discovery
Data-driven p2p streaming Recommend papers are measurement
studies of PPLive
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Case Study: PPLive
1. Contact channel server for available channels
2. Retrieve list of peers watching selected channel
3. Find active peers on channel to share video chunks Source: “Insights into PPLive: A Measurement
Study of a Large-Scale P2P IPTV System” by Hei et al.