topic.p2p - 1 Peer-to-Peer Networking 2 Client/Server...

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Unformatted text preview: 1 Peer-to-Peer Networking 2 Client/Server Systems: Scaling Problem b Millions of clients ⇒ server and network meltdown 3 P2P System b Leverage the resources of client machines (peers) c Computation, storage, bandwidth 4 Why p2p? b Harness lots of spare capacity c 1 Big Fast Server: 1Gbit/s, $10k/month++ c 2,000 cable modems: 1Gbit/s, $ ?? c 1M end-hosts: Uh, wow. b Build self-managing systems / Deal with huge scale c Same techniques attractive for both companies / servers / p2p • E.g., Akamai’s 14,000 nodes • Google’s 100,000+ nodes 5 Outline b p2p file sharing techniques c Downloading • Whole-file vs. chunks c Searching • Centralized index (Napster, BitTorrent, etc.) • Flooding (Gnutella, etc.) • Smarter flooding (KaZaA, etc.) • Routing (Freenet, DHTs, etc.) b Uses of p2p - what works well, what doesn’t? c servers vs. arbitrary nodes c Hard state (backups!) vs soft-state (caches) b Challenges c Fairness, freeloading, security, … Credit: Based on slides from Robert Morris & Srini Seshan 6 P2p file-sharing b Quickly grown in popularity c Hundreds of file sharing applications c 35 million American adults use P2P networks -- 29% of all Internet users in US! c P2P accounts for a significant fraction of Internet traffic • Q : What dominates Internet traffic, P2P or HTTP? • A : HTTP (before 2001/2002); P2P (2002-07); HTTP (2007+) 7 What’s out there? DHTs eDonkey2000 KaZaA (bytes, not chunks) BitTorrent Chunk Based Freenet Gnutella Napster Whole File Route Super- node flood Flood Central 8 The search problem Internet N 1 N 2 N 3 N 6 N 5 N 4 Publisher Key=“title” Value=MP3 data… Client Lookup(“title”) ? 9 Search: key issues b Needles vs. Haystacks c Searching for top 40, or an obscure punk track from 1981 that nobody’s heard of? b Search expressiveness c Whole word? Regular expressions? File names? Attributes? Whole-text search? • (e.g., p2p gnutella or p2p google?) 10 Framework b Common Primitives: c Join : how do I begin participating? c Publish : how do I advertise my file? c Search : how do I find a file? c Fetch : how do I retrieve a file? 11 Next Topic... b Centralized Database c Napster b Query Flooding c Gnutella b Intelligent Query Flooding c KaZaA b Swarming c BitTorrent b Real-time p2p c skype b Structured Overlay Routing c Distributed Hash Tables 12 Napster: History b 1999: Sean Fanning launches Napster b Peaked at 1.5 million simultaneous users b Jul 2001: Napster shuts down 13 Napster: Overiew b Centralized Database: c Join : on startup, client contacts central server c Publish : reports list of files to central server c Search : query the server => return someone that stores the requested file c Fetch : get the file directly from peer 14 Napster: Publish I have X, Y, and Z!...
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