Terminology of BitTorrent
Encyclopedia
This list explains terms used when discussing BitTorrent client
s, and in particular the BitTorrent protocol used by these clients.
Hash
Index
Leech
Lurker
p2p
Scrape
Tracker
BitTorrent client
BitTorrent is a peer-to-peer program developed by Bram Cohen and BitTorrent, Inc. used for uploading and downloading files via the BitTorrent protocol. BitTorrent was the first client written for the protocol. It is often nicknamed Mainline by developers denoting its official origins. Since version...
s, and in particular the BitTorrent protocol used by these clients.
Availability
The number of full copies of a file (or set of files and directories) directly available to the client. Each seed adds 1.0 to this number, as they have one complete copy of the file. A connected peer with a fraction of the file available adds that fraction to the availability, if no other peer has this part of the file.- Example: a peer with 65.3% of the file downloaded increases the availability by 0.653. However, if two peers both have the same portion of the file downloaded - say 50% - and there is only one seeder, the availability is 1.5.
- Sometimes "distributed copies" is considered to be "availability minus 1". So if the availability is 1.6 , the distributed copies will be 0.6 because it is only counting the "copies" of the file.
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 (i.e., it is completely uninterested)
- The client is already uploading at its full capacity (it has reached the value of
max_uploads) - The second client has been blacklistedBlacklist (computing)In computing, a blacklist or block list is a basic access control mechanism that allows everyone access, except for the members of the black list . The opposite is a whitelist, which means allow nobody, except members of the white list...
for being abusive or is using a blacklisted BitTorrent client.
Client
- The program that enables p2pPeer-to-peerPeer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...
file sharingFile sharingFile sharing is the practice of distributing or providing access to digitally stored information, such as computer programs, multimedia , documents, or electronic books. It may be implemented through a variety of ways...
via the BitTorrent protocol. Examples of clients include µTorrent and VuzeVuzeVuze is a BitTorrent client used to transfer files via the BitTorrent protocol. Vuze is written in Java, and uses the Azureus Engine. In addition to downloading data linked to by .torrent files, Azureus allows users to view, publish and share original DVD and HD quality video content...
.
Downloader
- A downloader is any peer that does not have the entire file and is downloading the file. This term, used in Bram Cohen'sBram CohenBram Cohen is an American computer programmer, best known as the author of the peer-to-peer BitTorrent protocol, as well as the first file sharing program to use the protocol, also known as BitTorrent...
PythonPython (programming language)Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive...
implementation, lacks the negative connotation attributed to leech. Bram prefers downloader to leechLeech (computing)In computing and specifically Internet, a leech or leecher is one who benefits, usually deliberately, from others' information or effort but does not offer anything in return, or makes only token offerings in an attempt to avoid being called a leech...
because BitTorrent's tit-for-tat ensures downloaders also upload and thus do not unfairly qualify as leeches.
End Game
- Also known as Endgame Mode on many clients. BitTorrent has several download strategies for initializing a download, downloading normally among the middle of the torrent, and downloading the last few pieces (see below) of a torrent.
- In typical client operation the last download pieces arrive more slowly than the others. This is because the faster and more easily accessible pieces should have already been obtained. In order to prevent the last pieces becoming unobtainable BitTorrent clients attempt to get the last missing pieces from all of its peers. Upon receiving the last pieces a cancel request command is sent to other peers.
Fake
- A fake torrent is a torrent that does not contain what is specified in its name or description (e.g. a torrent is said to contain a video, but it contains only a snapshotSnapshot (photography)A snapshot is popularly defined as a photograph that is "shot" spontaneously and quickly, most often without artistic or journalistic intent. Snapshots are commonly considered to be technically "imperfect" or amateurish—out of focus or poorly framed or composed...
of a moment in the video, or in some cases a virus).
HashHash functionA hash function is any algorithm or subroutine that maps large data sets to smaller data sets, called keys. For example, a single integer can serve as an index to an array...
- The hash is a string of alphanumericAlphanumericAlphanumeric is a combination of alphabetic and numeric characters, and is used to describe the collection of Latin letters and Arabic digits or a text constructed from this collection. There are either 36 or 62 alphanumeric characters. The alphanumeric character set consists of the numbers 0 to...
characters (typically hexadecimal) in the .torrent file that the client uses to verify the data that is being transferred. Hash is the shorter form of the word HashsumCryptographic hash functionA cryptographic hash function is a deterministic procedure that takes an arbitrary block of data and returns a fixed-size bit string, the hash value, such that an accidental or intentional change to the data will change the hash value...
.
- Torrent files 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's General tab shows the number of these hash fails.
- Hash checks greatly reduce the chance that invalid data is incorrectly identified as valid by the BitTorrent client, but it is still possible for invalid data to have the same hash value as the valid data and be treated as such. This is known as a hash collisionHash collisionNot to be confused with wireless packet collision.In computer science, a collision or clash is a situation that occurs when two distinct pieces of data have the same hash value, checksum, fingerprint, or cryptographic digest....
. Torrent and p2p files typically use 160 bit hashes that are reasonably free from hash collision problems, so the probability of bad data being received and passed on is very rare.
Health
- Health is shown in a bar or in % usually next to the torrent's name and size, on the site where the
.torrentfile is hosted. It shows if all pieces of the torrent are available to download (i.e. 50% means that only half of the torrent is available).
IndexBitTorrent indexA BitTorrent index is a list of .torrent files , managed by a website, that is available for searching files to download through BitTorrent protocol. It should be differentiated from a BitTorrent tracker, which merely coordinates communication between peers attempting to download the payload of the...
- An index is a list of .torrent files (usually including descriptions and other information) managed by a websiteWebsiteA website, also written as Web site, web site, or simply site, is a collection of related web pages containing images, videos or other digital assets. A website is hosted on at least one web server, accessible via a network such as the Internet or a private local area network through an Internet...
and available for searches. An index website can also be a tracker.
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.
LeechLeech (computing)In computing and specifically Internet, a leech or leecher is one who benefits, usually deliberately, from others' information or effort but does not offer anything in return, or makes only token offerings in an attempt to avoid being called a leech...
- A leech is a term with two meanings. Primarily leech (or leeches) refer to a peer (or peers) who has a negative effect on the swarm by having a very poor share ratio (downloading much more than they upload, creating a ratio less than 1.0).
- Most leeches are users on asymmetric internet connections and do not leave their BitTorrent clientBitTorrent clientBitTorrent is a peer-to-peer program developed by Bram Cohen and BitTorrent, Inc. used for uploading and downloading files via the BitTorrent protocol. BitTorrent was the first client written for the protocol. It is often nicknamed Mainline by developers denoting its official origins. Since version...
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.
- 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 alternative meaning was mainly introduced by most BitTorrent tracker sites.
LurkerLurkerIn Internet culture, a lurker is a person who reads discussions on a message board, newsgroup, chatroom, file sharing, social networking site, listening to people in VOIP calls such as Skype and Ventrilo or other interactive system, but rarely or never participates actively...
- A lurker is a user that only downloads files from the group but does not add new content. It does not necessarily mean that the lurker will not seed. Not to be confused with a leecher.
p2pPeer-to-peerPeer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...
- Stands for "peer to peer", which is the technology used for file sharing among computer users over the internet. In a p2p network, each node (or computer on the network) acts as both a client and a server. In other words, each computer is capable of both sending and receiving data.
Peer
- A peer is one instance of a BitTorrent client running on a computer on the InternetInternetThe Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
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").
Piece
- This refers to the torrented files being divided up into equal specific sized pieces (e.g. 64kb, 128kb, 512Kb, 1Mb, 2Mb, 4Mb). The pieces are distributed in a randomRandomnessRandomness has somewhat differing meanings as used in various fields. It also has common meanings which are connected to the notion of predictability of events....
fashion among peers in order to optimize trading efficiency.
Ratio credit
- A ratio credit, also known as upload credit or ratio economy, is a currency system used on a number of private trackers to provide an incentive for higher upload/download ratios among member file-sharers. In such a system, those users who have greater amounts of bandwidth, hard drive space (particularly seedboxSeedboxA seedbox is a private dedicated server used for the uploading and downloading of digital files.Seedboxes generally make use of the BitTorrent protocol for uploading and downloading, although they have also been used on the eDonkey2000 network. Seedboxes are usually connected to a high speed...
es) or idle computer uptimeUptimeUptime is a measure of the time a machine has been up without any downtime.It is often used as a measure of computer operating system reliability or stability, in that this time represents the time a computer can be left unattended without crashing, or needing to be rebooted for administrative or...
are at a greater advantage to accumulate ratio credits versus those who are lacking in any one or more of the same resources.
ScrapeTracker scrapeA scrape, or tracker scrape, is a request sent by a BitTorrent client to a tracker. A request is sent, connection to the tracker is established, information is exchanged, then the connection is closed...
- 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.
Seed
- A Seed is used to refer to a peer who has 100% of the data. When a leech obtains 100% of the data, that peer automatically becomes a Seed.
- Seeding refers to leaving a peer's connection available for other peers, i.e. leeches, to download from. Normally, a peer should seed more data than leech. However, whether to seed or not, or how much to seed, is dependent on the availability of leeches and the choice of the peer at the seeding end.
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 negative connotation.
Snubbed
- An uploading client is flagged as snubbed if the downloading client has not received any data from it in over 60 seconds.
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 ABCABC (Yet Another BitTorrent Client)ABC is a free software, open source BitTorrent client based on BitTornado. It supports a queueing system with priority, global and local preference setting for downloading torrent , 3 upload options to do with completed file, and a system named Upload Rate Manager to force torrents out of queue...
, VuzeVuzeVuze is a BitTorrent client used to transfer files via the BitTorrent protocol. Vuze is written in Java, and uses the Azureus Engine. In addition to downloading data linked to by .torrent files, Azureus allows users to view, publish and share original DVD and HD quality video content...
, BitTornadoBitTornadoBitTornado is a free BitTorrent client for transfer of computer files over networks, including the Internet. It is developed by John Hoffman, who also created its predecessor, Shad0w's Experimental Client...
, TorrentStorm, and µTorrent have a "super-seedSuper-seedingSuper-seeding is a feature of some BitTorrent clients that attempts to minimize the amount of data which must be uploaded by the original seed until the first completion of a downloading peer. The feature was conceived by John Hoffman and first implemented in the BitTornado client in 2003...
" 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 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.
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.
Torrent
- A torrent can mean either a
.torrentmetadataMetadataThe term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
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 checksumsChecksumA checksum or hash sum is a fixed-size datum computed from an arbitrary block of digital data for the purpose of detecting accidental errors that may have been introduced during its transmission or storage. The integrity of the data can be checked at any later time by recomputing the checksum and...
of all pieces in the torrent. It also contains the address of a tracker that coordinates communication between the peers in the swarm.
TrackerBitTorrent trackerA BitTorrent tracker is a server that assists in the communication between peers using the BitTorrent protocol. It is also, in the absence of extensions to the original protocol, the only major critical point, as clients are required to communicate with the tracker to initiate downloads...
- 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.