Terminology of BitTorrent

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

availability: (also distributed copies) The number of full copies of the file 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. (ie. 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).

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 (ie. the value for max_uploads has been reached)

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

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.

leech: A leech is usually 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. The term leech, however, can be used simply to describe a peer - or any client that does not have 100% of the data.

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 has downloaded.

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").

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.

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 are for completion of the file.

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 ABC, Azureus, BitTornado, TorrentStorm, and µTorrent have a "superseed" 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.

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 .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.

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] See also

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