Peer-to-Peer (P2P) Networking 2013 Client/Server Architecture GET /index.html HTTP/1.0 HTTP/ OK... Clients Server Peer-to-Peer Architecture Peers Gateway Server 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 The Client Side Todays clients can perform more roles than just forwarding users requests Todays clients have: more computing power more storage space Thin client Fat client Evolution at the Client Side IBM 8-bit 4.77MHz 360k diskettes 64-bit 4-core 4GHz 750GB HD DECS VT100 No storage 70 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? Peer-to-Peer (P2P) 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) Resources Sharing What can we share? Computer-related resources Shareable related-computer resources: CPU cycles - GIMPS Bandwidth - PPLive, PPStream Storage Space - OceanStore, Murex Data - Napster, Gnutella People - Buddy Finder Camera, Microphone, Sensor, Service??? SETI Search for Extra-Terrestrial 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 - Example MUREX: A Mutable Replica Control Scheme for Peer-to-Peer Storage Systems Jehn-Ruey Jiang ACN Lab NCU Murex: Basic Concept HotOS Attendee Peer-to-Peer Video Streaming Video stream Napster -- Shawn Fanning 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 beastieboy makes direct connection to kingrook for file transfer song5 beastieboy song1.mp3 song2.mp3 song3.mp3 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) Gnutella -- Justin Frankel and Tom Pepper The Animal GNU Gnutella = GNUGNU: Recursive Acronym GNUs Not Unix . + Nutella: a hazelnut chocolate spread produced by the Italian confectioner Ferrero . GNU Nutella 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 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, 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. 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 Peer-to-Peer Overlay Network Focus at the application layer Peer-to-Peer Overlay Network Internet End systems one hop (end-to-end comm.) a TCP thru the Internet Topology of a Gnutella Network xyz.mp3 ? Gnutella: Issue a Request Gnutella: Flood the Request xyz.mp3 Gnutella: Reply with the File Fully distributed storage and directory! 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 We Want Efficiency : O(log(n)) messages per lookup Scalability : O(log(n)) state per node Robustness : surviving massive failures 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! Example of Hasing Shark SHA-1 Object ID (key):DE11AC SHA-1 Object ID (key):AABBCC :8080 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 Mapping an object to the closest node with a larger key 0 M - an data object - a node Viewed as a Distributed Hash Table Hash table Peer node Internet 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 nodes 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 How to Find an Object? Hash table Peer node 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 Peer node i+2 2 i+2 4 i+2 8 i 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) Im node 2. Please find key 14! StartInt.node 10+1[11,12) [12,14) [14,2) [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 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 Q&A