This document discusses the past, present, and future of peer-to-peer (P2P) networks. It describes how P2P networks emerged to help alleviate load on servers and make use of the interconnectivity between nodes. Popular early P2P file sharing applications like Napster, Gnutella, and BitTorrent are discussed. While P2P file sharing declined due to legal issues, P2P protocols now see growing use for media streaming, communication, and within data centers. The document predicts P2P will continue evolving with technologies like IPv6 and play an increasing role in areas like social networks and peer production.

1. Peer-to-peer: past, present, future
Cristina Cărbunaru
16 February 2011

2. Peer-to-peer
 Internet today
◦ Large number of hosts
◦ Large amount of content
 Significant challenges for traditional
client-server architectures
 Make use of the inter-connectivity of
the nodes in the Internet
◦ Alleviate the load from servers
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3. Client-server vs. P2p
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4. The Peer
 Double function:
◦ Client - consumer
◦ Server - producer
 Incentives to offer service, not just
benefit from service
 More peers means more capacity
added to the system
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5. P2p Goals
 Reduced central control
 Heterogeneity
 Flat topology
 Autonomy
 Fault resilience
…
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6. History
 File sharing applications
◦ 1999: Napster
◦ Gnutella, Kazaa, Freenet
◦ 2001: BitTorrent (Bram Cohen)
◦ Multiple variations of p2p programs
 Nowadays:
◦ File sharing – among individual users or in
the data centers
◦ Media streaming – on-demand or live content
◦ Communication – Skype!
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7. The beginnings: Napster
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8. BitTorrent
Seed
Tracker
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9. BitTorrent
Seed
Leecher
Tracker
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10. BitTorrent
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11. BitTorrent
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12. BitTorrent
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13. BitTorrent
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14. BitTorrent
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15. BitTorrent
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16. BitTorrent
Free-rider
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17. Swarm Behavior
 Incentive mechanisms
◦ Why offer service?
 Flash crowd
◦ Large number of peers choke the
performance
 Steady state
◦ Number of peers stays constant over time
◦ Easy to predict performance
 Lifetime
◦ When and why is the torrent dying?
 ...
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18. Peer Behavior
 Free riding
◦ Evaluate performance loss
◦ Methods to prevent
 Best results with minimum of effort
◦ Cheating, but not exactly
 Clustering of peers
◦ Peers download/upload to similar bandwidth
peers
 Security of content
◦ Malicious data
 Connectivity
◦ NAT boxes
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19. Approaches
 Measurement
◦ Real swarms
◦ Experimental platforms: PlanetLab, EmuLab
 Simulation
 Modeling
 Proposing new p2p protocols that solve
different problems
◦ Proportional upload bandwidth: PropShare
◦ Amount of data transferred: Avalanche
◦ Upload bandwidth allocation among peers to
get the best download speed: BitTyrant
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20. P2p in 2008/2009 (Ipoque study)
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21. Popularity
 Decreasing popularity for p2p file
sharing
◦ Packet filtering
◦ Packet inspection
◦ Lawsuit against Pirate Bay
◦ …
 One click file hosting services
(Rapidshare, Hotfile) become popular
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22. What to Research?
 Packet filtering
◦ Glasnost
 Hiding identity
◦ Tor
◦ Anonymous p2p
 Copyright issues
◦ Download might be legal in some
countries
◦ Upload is illegal
 …
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23. What’s Next?
 Increasing usage of p2p protocols in
other contexts:
◦ Media streaming, communication
◦ Inside the data centers
◦ Social networks
◦ Economics
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24. Future
 New technologies
◦ IPv6
◦ Mobile devices
 From computer-to-computer to
human-to-human
◦ commons-based peer production (Yochai
Benkler):
 Peer governance
 Peer property
 Peer distribution
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25. Conclusions
 Successful piece of research
◦ P2p transcended computer science
 Changed the way we share
◦ Files
◦ Knowledge
◦ Peer generated content
 P2p is here to stay!
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26. Questions?
Thank you!
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