Chapter2_P2P - Peer-to-Peer File Sharing Systems...

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1 1 Peer-to-Peer File Sharing Systems z Peer-to-Peer: decentralized computing model z What is a Peer? – Information producer, disseminator, or consumer. . z Why is it useful? – Solves some problems of client/server model, like; • hot spots surrounding big servers • resource under-utilization on client side 2 Some Popular P2P Systems 3 Peer-to-Peer Systems: Structured and Unstructured Structured P2P: P2P network topology is tightly controlled and files are placed not at random nodes but at specified locations that will make subsequent queries easier to satisfy. Examples: CAN, Chord, Pastry …… Unstructured P2P: no precise control over the network topology or file placement. The placement of files is not based any knowledge of the topology. Examples: Napster, Gnutella, KaZaA 4 Unstructured P2P z Centralized Model: Napster z Decentralized Model: Gnutella, Freenet z Hierarchical Model: KaZaA, Morpheus 5 Centralized Model Original Napster design 1) when peer connects, it informs central server: – IP address –c o n t e n t 2) A sends a query 3) A requests file from B centralized directory server peers A B 1 1 1 1 2 3 6 Problems With Centralized Directory Single point of failure Performance bottleneck Copyright infringement file transfer is decentralized, but locating content is highly centralized
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2 7 History of Napster z 1999/1: Shawn Fanning (freshman, Northeastern), dropped out and started it. z 1999/6: Napster began operations for swapping music among peers. z 1999/12: lawsuit on copyright violation (RIAA), asking for $100K of each. z 2000/3: universities ban it due to heavy traffic, e.g. 25% traffic in Uwisc. z 2000/5: VC firm Hummer Winblad invested $15 millions to Napster. z 2000/7/26: US District judge orders to stop Napster s operations in 2 days. z 2000/7/28: 9th US Circuit Appeals Court rules it is allowed to continue. z 2001/2: Federal Appeals Court rules it must stop trading copyrighted music. z 2001/9: It reaches a settlement with music writers/publishers: pay $26 M for the past damage and a % to them as it starts as a paying service in 2002. z Triggered other P2P file sharing applications and research in P2P 8 Decentralized Model Query flooding (Gnutella) Send query to neighbors Neighbors forward query If queried peer has object, it sends message back to querying peer TTL is mechanism to limit query distance. TTL(Time To Live): the number of times a query will be forwarded before it is removed from the network. query 9 Gnutella: Bootstrapping Some well known bootstrapping servers keep a list of some peering nodes When a new peer wants to join a P2P network, it contacts a bootstrapping server, the IP addresses of a list of existing peers are provided. The new peer then tries to connect with some of these peers.
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Chapter2_P2P - Peer-to-Peer File Sharing Systems...

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