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Bittorrent final seminar


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A seminar on BitTorrent Protocol.....

A seminar on BitTorrent Protocol.....

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  • 1. Seminar on : A Peer-to-peer Network System Presented By : Chirodeep Das. BCSE-IV. Roll-000810501008. Jadavpur University.
  • 2.  Introduction Why “BitTorrent”? Traditional Client-server System Peer to peer network system What is “ BitTorrent ”? BitTorrent components How BitTorrent works? Pictorial explanation on the Working Piece Selection Mechanisms Advantages Some Facts Conclusion References
  • 3.  BitTorrent is a peer to peer (P2P) file transferring system and was designed in April 2001 by Brahm Cohen and then maintained by Cohen’s company BitTorrent, Inc. Unlike other traditional download methods, BitTorrent maximizes transfer speed by locating the pieces of the file you want and downloading these pieces simultaneously from people who already have them. This process makes popular and very large files download much faster . This is more popular and efficient file transferring system than the traditional client – server system.
  • 4.  Client-server computing or networking is an application architecture that partitions the work loads between service providers (servers) and service requesters, called clients. Millions want to download the same popular huge files 1. Softwares 2. Media (the real example!) You open a Web page and click a link to download a file to your computer. The Web browser software on your computer (the client) tells the server (a central computer that holds the Web page and the file you want to download) to transfer a copy of the file to your computer. The transfer is handled by a protocol (a set of rules), such as FTP (File Transfer Protocol) or HTTP (Hypertext Transfer Protocol).
  • 5. Overloaded!SourceRouter“Interested” End-host
  • 6.  Client-server model fails if  Single server fails or  Can’t afford to deploy enough servers Another issue is huge Traffic Overload in the server(s) which is the central point of failure.
  • 7.  BitTorrent is a peer-to-peer file sharing protocol allowing users to distribute large amounts of data without putting the level of strain on their computers that would have been needed for standard Internet hosting. Peer-to-peer file sharing is different from traditional file downloading. In peer-to-peer sharing, you use a software program (rather than your Web browser) to locate computers that have the file you want to download. Because these are ordinary computers like yours, as opposed to servers;they are called peers.
  • 8. tracker Peer Each peer is directly connected to other peer. The file to be transferred is divided into equal size of pieces. Peer uploads the pieces it has while downloads any piece it can get from other peers. These pieces are downloaded from different peers parallely. It is used for large file transfer.
  • 9.  No central point of failure ✓E.g. the internet & the web do not have a central point of failure. ✓Most internet & web services use the client-server model (e.g. HTTP) so a specific service does have a central point of failure.Scalability ✓Since every peer is alike, it is possible to add more peers to the system and scale to larger networks.
  • 10. Like most Internet phenomena, Bit Torrenthas its own jargon. Some of the most common termsrelated to BitTorrent include: BitTorrent Client Software .torrent file or METAinfo file Leechers Peers Seeds Swarm Tracker Piece (of a file) Torrent index server
  • 11.  Client S/W – program which resides on a peers’ computer and implements the BitTorrent protocol. It controls all operations such as : reads information present in the .torrent file. After reading .torrent file it sends message to tracker to send the list of peers and then it connects to peers. It keeps all record of the file which is receiving.
  • 12.  It has extension as .torrent and downloaded from torrent index server. Contains the information that points to the actual file and the people who are sharing it. The main contents of the .torrent file are -  Name/size/date for each .torrent file.  # no. of pieces of each files.  SHA-1 hash of each file for maintaining the data integrity.  Trackers associated with that torrent.
  • 13.  These are the clients who have entire file.  They upload pieces of the file to other peers.  These are the clients who do not have the entire file.  They upload the parts of file they have at the same time when they download other parts. These are the clients who are responsible for the file transfer. Peers = leechers + seeds. Downloading speed of any file using torrent depends on number of peers.
  • 14. 1 2 3 4 5 6 7 8 The file which is to be downloaded is divided into similar size of pieces. Several pieces are downloaded parallelly. Each piece is downloaded from different peers.
  • 15.  Tracker is the server that manages the BitTorrent file transfer process. It provides all list of peers which are associated with a particular torrent. These trackers are mentioned in the Metafile. Client S/W sends request to the tracker to send the list of peers and after getting the complete list of peers client s/w connects to the peers. The group of computers that are simultaneously sending (uploading) or receiving (downloading) the same file is called Swarm.
  • 16.  Source of .torrent files Torrent search engine
  • 17. PIECES
  • 18. PEERS
  • 19.  Initial seeder chops file into many pieces. Leecher first locates the .torrent file that directs it to a tracker, which tells which other peers are downloading that file. As soon as a leecher downloads pieces of the file, replicas of the pieces are created. More downloads mean more replicas are available. As soon as a leecher has a complete piece, it can potentially share it with other downloaders. Eventually each leecher becomes a seeder by obtaining all the pieces, and assembles the file. Finally it verifies the checksum using SHA-1.
  • 20.  1. Seeder generates a torrent file Uploads torrent to a web server. Seeder – A client sharing 100% of the shared file.
  • 21.  2. The seeder notifies the tracker that it is sharing the file described in the torrent file.
  • 22.  3. A leecher downloads the torrent file from some torrent index server. Leecher – client which has some parts and downloads the other parts of the shared file from the seeder.
  • 23.  4.The leecher (client) connects to the tracker(s) specified in the torrent metafile. The tracker returns a list of other peers who are sharing the file.
  • 24.  5. The leecher connects to its peers to retrieve pieces of the files.
  • 25. A machine with a complete copy (the seed) can distribute incomplete pieces to Seed multiple peersPeers exchangedifferent pieces of As soon as the user hasthe file with one a piece of the file on hisanother until they machine, he canassemble a whole become a source of that piece to other peers, helping speed download
  • 26. Torrent Tracker
  • 27. torrent: group oftracker: tracks peers peers exchangingin torrent; provides chunks of a filetracker list trading chunkstorrent index server: peersearch for torrents;provides .torrent file
  • 28.  The order in which pieces are selected by different peers is critical for good performance. If an inefficient policy is used, then peers may end up in a situation where each has all identical set of easily available pieces, and none of the missing ones. If the original seed is prematurely taken down, then the file cannot be completely downloaded! What are ―good policies?‖ Some piece(chunk) selection mechanisms are- Rarest Piece First  General rule Random First Piece  Special case, at the beginning Endgame Mode  Special case, at the end
  • 29.  Initially, a peer has nothing to trade. So it is important to get a complete piece as early as possible. Policy is to select a random piece of the file and download it.
  • 30.  Determine the pieces that are most rare among your peers, and download those first. This ensures that the most commonly available pieces are left till the end to download. It also ensures that a large variety of pieces are downloaded from the seed.
  • 31.  Near the end, missing pieces are requested from every peer containing them. When the piece arrives, the pending requests for that piece are cancelled. This ensures that a download is not prevented from completion due to a single peer which has a slow transfer rate. Some bandwidth is wasted, but in practice, this is not too much.
  • 32.  Once download is complete, a peer has no download rates to use for comparison nor has any need to use them. The question is, which nodes to upload to? Policy: Upload to those peers with the best upload rate. This ensures that pieces get replicated faster, and new seeders are created fast.
  • 33.  BitTorrent is an open-source program that offers a spyware- and nuisance-free installation. Allows users to share large amounts of data in a short span of time. Discourages ―freeloading‖ or ―free riders‖ (those who only download but never upload) by rewarding the fastest uploaders. The more popular a file is — the more people want a copy of it — the faster it can be downloaded, because there are lots of replicas already present in the system.
  • 34.  Bit torrent is responsible for roughly 27-55% of all internet traffic and 45-78% of P2P traffic. As of 2011 bitTorrent has more than 100 million users and grater share of bandwidth than Netflix and Hulu combined. THE PIRATE BAY: Who in september 2008 had 69,12,029 visits and 21,40,325 unique visitors making it 109th most popular website Another popular torrent tracker isoHunt claims to have 9857 TB of data
  • 35.  BitTorrent is a great protocol with its huge potential to distribute large files very easily. Bit Torrent is conceived as a way of distributing large and popular file more quickly, efficiently, and reliably. As a P2P file sharing system BitTorrent is quickly becoming the method of choice for publishing and sharing large files across the internet.
  • 36.  king_bittorrent.html
  • 37. Thank you!!