Terminology of BitTorrent

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This list explains terms used when discussing BitTorrent clients, and in particular the BitTorrent protocol used by these clients.

[edit] Common BitTorrent terms

[edit] Announce

Same as "scrape" (see below), but a client also announces that it wants to join the swarm and that server should add it to the peers in that swarm.

[edit] Choked

Describes a peer to whom the client refuses to send file pieces. A client chokes another client in several situations:

The second client is a seed, in which case it does not want any pieces (ie. it is completely uninterested)
The client is already uploading at its full capacity (it has reached the value of max_uploads)

[edit] Client

The program that enables p2p file sharing via the BitTorrent protocol. Examples of clients include µTorrent and Vuze.

[edit] Downloader

A downloader is any peer that does not have the entire file and is downloading the file. This term, used in Bram Cohen's Python implementation, lacks the negative connotation attributed to leech. Bram prefers downloader to leech because BitTorrent's tit-for-tat ensures downloaders also upload and thus do not unfairly qualify as leeches.

[edit] End Game

Bittorrent has a couple of download strategies for starting of a download, normal download and downloading the end of a torrent. Typically, the last download pieces arrive slowly, so to prevent this, bittorrent would attempt to get the last missing pieces from all of its peers. Upon receiving a piece, a cancel request command is sent to other peers.

[edit] Hash

The hash is a string of alphanumeric characters in the .torrent file that the client uses to verify the data that is being transferred. It contains information like the file list, sizes, pieces, etc. Every piece received is first checked against the hash. If it fails verification, the data is discarded and requested again. The 'Hash Fails' field in the torrent General tab shows the number of these hash fails.

[edit] Index

An index is a list of .torrent files (usually including descriptions and other information) managed by a website and available for searches. An index website can also be a tracker.

[edit] Interested

Describes a downloader who wishes to obtain pieces of a file the client has. For example, the uploading client would flag a downloading client as 'interested' if that client did not possess a piece that it did, and wished to obtain it.

[edit] Leech

A leech is a term with two meanings. Usually it is used to refer a peer who has a negative effect on the swarm by having a very poor share ratio - in other words, downloading much more than they upload. Most leeches are users on asymmetric internet connections and do not leave their BitTorrent client open to seed the file after their download has completed. However, some leeches intentionally avoid uploading by using modified clients or excessively limiting their upload speed. However the often used second meaning of leech is synonymous with downloader (see above) - used simply to describe a peer - or any client that does not have 100% of the data. This other meaning is mainly caused by most BitTorrent tracker sites using term leech in this sense.

[edit] Lurker

A lurker is a user that only downloads files from the group but does not add new content. Unlike a leech, a lurker will seed what he or she has downloaded.

[edit] p2p

Stands for "peer to peer" which is the technology used for file sharing among computer users over the internet.

[edit] Peer

A peer is one instance of a BitTorrent client running on a computer on the Internet to which other clients connect and transfer data. Usually a peer does not have the complete file, but only parts of it. However, in the colloquial definition, "peer" can be used to refer to any participant in the swarm (in this case, it's synonymous with "client").

[edit] Piece

This refers to the torrented files being divided up into equal specific sized pieces (ie 512Kb, 1Mb). The pieces are distributed in a random fashion among peers in order to optimize trading efficiency.

[edit] Scrape

This is when a client sends a request to the tracking server for information about the statistics of the torrent, such as with whom to share the file and how well those other users are sharing.

[edit] Seeder

A seeder is a peer that has a complete copy of the torrent and still offers it for upload. The more seeders there are, the better the chances of getting a higher download speed.

[edit] Share ratio

A user's share ratio for any individual torrent is a number determined by dividing the amount of data that user has uploaded by the amount of data they have downloaded. Final share ratios over 1 carry a positive connotation in the BitTorrent community because they indicate that the user has sent more data to other users than they received. Likewise, share ratios under 1 have a negative connotation.

[edit] Snubbed

An uploading client is flagged as snubbed if the downloading client has not received any data from it in over 60 seconds.

[edit] Super-seeding

When a file is new, much time can be wasted because the seeding client might send the same file piece to many different peers, while other pieces have not yet been downloaded at all. Some clients, like ABC, Azureus, BitTornado, TorrentStorm, and µTorrent have a "super-seed" mode, where they try to only send out pieces that have never been sent out before, theoretically making the initial propagation of the file much faster. However the super-seeding becomes substantially less effective and may even reduce performance compared to the normal "rarest first" model in cases where some peers have poor or limited connectivity. This mode is generally used only for a new torrent, or one which must be re-seeded because no other seeds are available.

[edit] Swarm

Together, all peers (including seeders) sharing a torrent are called a swarm. For example, six ordinary peers and two seeders make a swarm of eight.

[edit] Torrent

A torrent can mean either a .torrent metadata file or all files described by it, depending on context. The torrent file contains metadata about all the files it makes downloadable, including their names and sizes and checksums of all pieces in the torrent. It also contains the address of a tracker that coordinates communication between the peers in the swarm.

[edit] Tracker

A tracker is a server that keeps track of which seeds and peers are in the swarm. Clients report information to the tracker periodically and in exchange receive information about other clients to which they can connect. The tracker is not directly involved in the data transfer and does not have a copy of the file.

[edit] References

[edit] See also

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