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Bit Torrent Protocol

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  • 1. CONTENTS  INTRODUCTION  OTHER FILE TRANSFOR METHODS  STRIKING CHARACTERISTICS  TERMINOLOGY  ARCHITECTURE OF BITORRENT  COMPONENTS OF BITTORRENT SYSTEM  WORKING OF BITTORRENT  CONCLUSION
  • 2.  Bit torrent is created by bram cohen  Transfer of large files using the minimum internet bandwidth  Peer-to-peer file transfer protocol  Files are shared by many users  Active participation of all users  Huge success in the file sharing domain  35% of internet traffic Introduction
  • 3. Other File Transfer Methods  Typical HTTP file transfer  Download Accelerator Plus (DAP)  Other Peer to Peer systems • Kazaa, eDonkey, Direct Connect ….
  • 4. Striking Characteristics  A central server is not needed  No single point of failure  More the number of users, greater will be the transfer rate  Data available in pieces, not as a single large file
  • 5. Terminology  Torrent  Peer  Seed  Leecher  Swarm  Reseed  Tracker  Share Ratio
  • 6. Architecture of BitTorrent
  • 7. HTTP Peer – Tracker TCP Peer – Peer Components of BitTorrent System  Metainfo File  Data  Tracker  Peers  Client
  • 8. Metainfo file  Containes all information about a torrent  File with a .torrent extension  Encoding scheme used by bittorrent is called bencoding  Hash of all the pieces are present in info field of metainfo file
  • 9. Data  Data can be a single file or multiple files contained in a directory  Data is split into many pieces of equal size  Each piece is further divided into many blocks  A piece will have a hash, needed for data integrity check  Common piece sizes are 256kb, 512kb and 1mb
  • 10. Tracker  Manages users participating in a torrent  Helps peers find each other  It is a HTTP service that works on port 6969  Peers request tracker for other peers having the required pieces  Tracker responds with a list of peers that have the requested piece  A tracker can manage many torrents
  • 11. Scraping  Querying the state of a given torrent  Tracker responds with a scrape page Announce URL : http://example.com/announce Scrape URL : http://example.com/scrape  Scrape page has the following keys • complete • incomplete • downloaded
  • 12. Peers  Ports 6881 – 6889 are used by peers  Peers speak TCP  Following are the key strategies used by peers while sharing files • Random First Piece • Rarest First • Endgame Mode • Peer Distribution • Choking • Optimistic Unchoking
  • 13.  Peers perform a handshake to start the communication  Handshaking involves these messages • Character 19 followed by ‘BitTorrent Protocol’ • 20 bytes hash of the info field from metainfo file • 20 bytes peer id  Peers start talking to each other  They pass a number of messages between them to send data and control the interactions
  • 14. Client  Executable program running on user’s machine  Co ordinates with OS to perform read write operations  A .torrent file must be opened by the client  Peers with same client perform better
  • 15. Working of BitTorrent 1. Seeder generates a torrent file and uploads torrent to a web server. 2. The seeder notifies the tracker that it is sharing the file described in the torrent file.
  • 16. 3. A leecher downloads the torrent file from the web server. 4. The leecher connects to the tracker specified in the torrent file.
  • 17. 5. The leecher connects to its peers to retrieve pieces of the files.
  • 18. Conclusion  BitTorrent is a popular P2P technology deployed across the Internet.  The protocol has found a niche as a preferred method for the decentralized distribution of large files.  It provides data integrity which ensures that the data will always be genuine and free from flaws.  BitTorrent uses tit for tat exchange to increase cooperation among peers and has developed a reputation for being efficient, scalable, and robust.
  • 19. References:  Cohen, Bram. “Incentives Build Robustness in BitTorrent. 2003. http://www.bittorrent.com/bittorrentecon.pdf  BitTorrent Protocol. http://www.bittorrent.org/protocol.html
  • 20. THANK YOU