1. P2P Networking

2. Client/Server Architecture GET /index.html HTTP/1.0 HTTP/1.1 200 OK... Clients Server 2/66

3. Peer-to-Peer Architecture Peers 3/66 Gateway Server

4. Server-based architecture  Client-Server / Server-Cluster  Problems ： Limited resources All loads are centered on the server  Server-based architecture has low scalability.  The setup and maintenance cost is high. Peer-to-Peer (P2P) architecture  Advantages ： Distributing loads to all users Users consume and provide resources  P2P architecture has high scalability.  The setup and maintenance cost is low. The architectures

5. The Client Side Today’s clients can perform more roles than just forwarding users requests Today’s clients have:  more computing power  more storage space Thin client  Fat client 5/66

6. Evolution at the Client Side IBM PC @ 4.77MHz 360k diskettes PC @ 4-core 4GHz 300GB HD DEC’S VT100 No storage ‘70‘80 2008 6/66

7. What Else Has Changed? The number of home PCs is increasing rapidly Most of the PCs are “fat clients” As the Internet usage grow, more and more PCs are connecting to the global net Most of the time PCs are idle How can we use all this? 7/66 Peer-to-Peer (P2P)

8. What is peer-to-peer (P2P)? “Peer-to-peer is a way of structuring distributed applications such that the individual nodes have symmetric roles. Rather than being divided into clients and servers each with quite distinct roles, in P2P applications a node may act as both a client and a server.” -- Charter of Peer-to-peer Research Group, IETF/IRTF, June 24, 2004 (http://www.irtf.org/charters/p2prg.html) 8/66

9. Resources Sharing What can we share?  Computer-related resources Shareable related-computer resources:  CPU cycles - seti@home, GIMPS  Bandwidth - PPLive, PPStream  Storage Space - OceanStore, Murex  Data - Napster, Gnutella  People - Buddy Finder  Camera, Microphone, Sensor, Service??? 9/66

10. SETI@Home SETI – Search for Extra-Terrestrial Intelligence @Home – On your own computer A radio telescope in Puerto Rico scans the sky for radio signals Fills a DAT tape of 35GB in 15 hours That data have to be analyzed 10/66

11. SETI@Home - Example

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16. MUREX: A Mutable Replica Control Scheme for Peer-to-Peer Storage Systems

17. Murex: Basic Concept HotOS Attendee

18. Peer-to-Peer Video Streaming 18/66 … … Video stream

19. 19/51 Napster -- Shawn Fanning

20. Napster Sharing Style: hybrid center+edge “slashdot” song5.mp3 song6.mp3 song7.mp3 “kingrook” song4.mp3 song5.mp3 song6.mp3 song5.mp3 1. Users launch Napster and connect to Napster server 3. beastieboy enters search criteria 4. Napster displays matches to beastieboy 2. Napster creates dynamic directory from users’ personal.mp3 libraries Title User Speed song1.mp3 beasiteboy DSL song2.mp3 beasiteboy DSL song3.mp3 beasiteboy DSL song4.mp3 kingrook T1 song5.mp3 kingrook T1 song5.mp3 slashdot 28.8 song6.mp3 kingrook T1 song6.mp3 slashdot 28.8 song7.mp3 slashdot 28.8 5. beastieboy makes direct connection to kingrook for file transfer song5 “beastieboy” song1.mp3 song2.mp3 song3.mp3

21. History of Napster 5/99: Shawn Fanning (freshman, Northeastern University) founds Napster Online (supported by Groove) 12/99: First lawsuit 7/01: simultaneous online users 160K 6/02: file bankrupt … 10/03: Napster 2 (Supported by Roxio) (users should pay $9.99/month) 21/66

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23. Gnutella -- Justin Frankel and Tom Pepper 23/66

24. The ‘Animal’ GNU Gnutella = GNUGNU: Recursive Acronym GNU’s Not Unix …. + Nutella: a hazelnut chocolate spread produced by the Italian confectioner Ferrero …. GNU Nutella

25. 25/51 GNU GNU's Not Unix 1983 Richard Stallman (MIT) established Free Software Foundation and Proposed GNU Project Free software is not freeware GPL: GNU General Public License

26. Gnutella History Gnutella was written by Justin Frankel, the 21-year-old founder of Nullsoft. (Nullsoft acquired by AOL, June 1999) Nullsoft (maker of WinAmp) posted Gnutella on the Web, March 14, 2000. A day later AOL yanked Gnutella, at the behest of Time Warner. Too late: 23k users on Gnutella People had already downloaded and shared the program. Gnutella continues today, run by independent programmers. 26/66

27. Gnutella Protocol Scenario: Joining Gnutella Network A Gnutella Network The new node connects to a well known ‘Anchor’ node or ‘Bootstrap’ node. Then sends a PING message to discover other nodes. PONG messages are sent in reply from hosts offering new connections with the new node. Direct connections are then made to the newly discovered nodes. New PING PONG 27/66

28. 28/51 Peer-to-Peer Overlay Network Focus at the application layer

29. 29/51 Peer-to-Peer Overlay Network Internet End systems one hop (end-to-end comm.) a TCP thru the Internet

30. 30/51 Topology of a Gnutella Network

31. xyz.mp3 ? Gnutella: Issue a Request

32. Gnutella: Flood the Request

33. xyz.mp3 Gnutella: Reply with the File Fully distributed storage and directory!

34. 34/51 So Far Centralized : - Directory size – O(n) - Number of hops – O(1) Flooded queries: - Directory size – O(1) - Number of hops – O(n) n: number of participating nodes

35. 35/51 We Want Efficiency : O(log(n)) messages per lookup Scalability : O(log(n)) state per node Robustness : surviving massive failures

36. 36/51 How Can It Be Done? How do you search in O(log(n)) time?  Binary search You need an ordered array How can you order nodes in a network and data objects?  Hash function!

37. 37/51 Example of Hasing Shark SHA-1 Object ID (key):DE11AC SHA-1 Object ID (key):AABBCC 194.90.1.5:8080

38. 38/51 Basic Idea Hash key Object “y” Objects have hash keys Peer “x” Peer nodes also have hash keys in the same hash space P2P Network yx H(y)H(x) Join (H(x)) Publish (H(y)) Place object to the peer with closest hash keys

39. 39/51 Mapping an object to the closest node with a larger key 0 M - an data object - a node

40. 40/51 Viewed as a Distributed Hash Table Hash table 02 128 -1 Peer node Internet

41. 41/51 DHT Distributed Hash Table Input: key (file name) Output: value (file location) Each node is responsible for a range of the hash table, according to the node’s hash key. Objects’ directories are placed in (managed by) the node with the closest key It must be adaptive to dynamic node joining and leaving

42. 42/51 How to Find an Object? Hash table 02 128 -1 Peer node

43. 43/51 Simple Idea Track peers which allow us to move quickly across the hash space  a peer p tracks those peers responsible for hash keys (p+2 i -1), i=1,..,m Hash table 02 128 -1 Peer node i+2 2 i+2 4 i+2 8 i

44. 44/46 Chord Lookup – with finger table StartInt.node 2+1[3,4)3 2+2[4,6)7 2+4[6,10)7 2+8[10,2)10 12 142 10 15 1 3 7 I’m node 2. Please find key 14! StartInt.node 10+1[11,12)12 10+2[12,14)12 10+4[14,2)14 10+8[2,10)2 O(log n) hops (messages) for each lookup!! 14 ∈ [10,2) 14 ∈ [14,2) Circular 4-bit ID space O(log n) states per node

45. 45/51 Hybrid P2P – Preserves some of the traditional C/S architecture. A central server links between clients, stores indices tables, etc  Napster Unstructured P2P – no control over topology and file placement  Gnutella, Morpheus, Kazaa, etc Structured P2P – topology is tightly controlled and placement of files are not random  Chord, CAN, Pastry, Tornado, etc Classification of P2P systems

46. 46/51 Q&A