Bit torrent Technology Done by: Swathi Raman 08D2754
BitTorrent Bram Cohen is the creator of BitTorrent, one of the most successful peer-to-peer programs ever. BitTorrent is a protocol (a set of rules that different computer systems agree to use) based on P2P that can be used to share large files very efficiently, using minimum bandwidth. It is just a tool used to download, it does not contain a built-in search facility. The .torrent files are usually located via HTTP thru search engines and trackers.
Torrent Lingo Torrent – At the beginning of all this is the torrent file itself. The .torrent file is not the entire file. It is extremely small and it just contains the information that points to the actual file and the people who are sharing it. It is like a map which is used by the BitTorrent client to assemble all the pieces together. BitTorrent client – A Bit Torrent client is one of the most important parts of the torrent process. It is a piece of software which takes the .torrent file, reads the information in it and starts the download. Peer - A peer is any computer participating in the download and upload of a torrent file.
(contd..) Seeder - A seed (or seeder) is anyone who has a complete copy of the file being shared across the torrent network. Leecher - A leech (or a leecher) is the person who does not have the complete file yet but has joined the network to download it. A leecher becomes a seeder when he downloads the entire file and then shares it across the network. Share ratio – The ratio is the amount of data a user has uploaded divided by the amount of data they have downloaded for a particular torrent (UL÷DL). A share ratio of 1+ has a positive effect on the user’s reputation because it means that the user has sent more data to other users than he has received. Conversely, share ratios under 1 have a negative effect.
(contd..) Swarm – The swarm is the sum total of all the leechers and seeders (i.e. all the computers) participating in the torrent process. Tracker – The tracker is a server which has the information of who has what files and who needs which ones, thus acting as a bridge between seeders and leechers. Some trackers are private requiring a registration where most are public. Index – An index is, as the name implies, a searchable list of .torrent files, hosted on a website.
Traditional Client-server downloading Client-server computing or networking is a distributed application architecture that partitions tasks or work loads between service providers (servers) and service requesters, called clients. It works like this: - 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).
Drawbacks Traffic congestion on the network has been an issue since the inception of the client-server paradigm. As the number of simultaneous client requests to a given server increases, the server can become overloaded. The client-server paradigm lacks the robustness of a good P2P network. Under client-server, should a critical server fail, clients’ requests cannot be fulfilled. In P2P networks, resources are usually distributed among many nodes.
The BitTorrent Protocol 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. Because these are ordinary computers like yours, as opposed to servers, they are called peers. 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 be needed for standard Internet hosting. The protocol works as an alternative data distribution method that makes even small computers with low bandwidth capable of participating in large data transfers.
COMPONENTS OF THE PROTOCOL Metainfo file- Describes metadata about the sharing file(s), and the tracker, and has the file ending .torrent. Tracker- A central server keeping track of peers and seeds sharing and downloading the file(s). Peer- A user on the network downloading the file(s), and sharing the parts that have been successfully downloaded. Seed- A peer that has the complete file or files available for sharing. At least one seed is needed in the beginning for the sharing to be possible. Client.-An application implementing the BitTorrent protocol.
Operation You open a Web page and click on a link for the file you want. BitTorrent client software communicates with a tracker to find other computers running BitTorrent that have the complete file and those with a portion of the file. The tracker identifies the swarm, which is the connected computers that have all of or a portion of the file and are in the process of sending or receiving it. The tracker helps the client software trade pieces of the file you want with other computers in the swarm. Your computer receives multiple pieces of the file simultaneously. If you continue to run the BitTorrent client software after your download is complete, others can receive .torrent files from your computer.
(contd..) Downloading pieces of the file at the same time helps solve a common problem with other peer-to-peer download methods: Peers upload at a much slower rate than they download. By downloading multiple pieces at the same time, the overall speed is greatly improved. The more computers involved in the swarm, the faster the file transfer occurs because there are more sources of each piece of the file.
Advantages BitTorrent is an open-source program offers a spyware- and nuisance-free installation. Allows users to share large amounts of data in a short span of time. Discourages “freeloading” by rewarding fastest uploaders. BitTorrent requires that users share files back with the community, so no one can get files without also giving files — this level of reciprocity makes the system stronger and faster. The more popular a file is — the more people want a copy of it — the faster it can be downloaded, because there are more places to get pieces of it.
(Contd..) Does not require high technical knowledge to use the BitTorrent- an average person needs not a user guide . By downloading a fraction of the file (1/10th) from ten to fifteen computers at the same time, the file is downloaded much faster. BitTorrent enables distributors to share the distribution load with all the people who get a copy of it, reducing the bandwidth burden on the distributor.
Limitations Lack of anonymity- BitTorrent does not offer its users anonymity. The leech problem- A BitTorrent user may often choose to leave the swarm as soon as they have a complete copy of the file they are downloading. The cheater problem- There are "cheating" clients like BitThief which claim to be able to download without uploading. Speed- Average BitTorrent download speed is limited by the combined average upload speed of "peers" (other nodes with partial copies which are also downloading) and "seeds" (complete copies that are only uploading).