computer science

Glossary of BitTorrent terms

Glossary of BitTorrent terms is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Glossary of BitTorrent terms rather than just read about it. In short: This is a glossary of jargon related to peer-to-peer file sharing via the BitTorrent protocol. Terms Availability (Also known as distributed copies.) The availability of each piece in the torrent is defined as the number of peers who have a copy of that piece.

Key takeaways

Glossary of BitTorrent terms belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Glossary of BitTorrent terms to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Glossary of BitTorrent terms from memory before moving on to harder problems.

Reference excerpt

This is a glossary of jargon related to peer-to-peer file sharing via the BitTorrent protocol.

Terms

Availability (Also known as distributed copies.) The availability of each piece in the torrent is defined as the number of peers who have a copy of that piece. The availability of the entire torrent is defined as the nonnegative real number whose integer part is the minimum piece availability and whose fractional part is the fraction of pieces that have higher availability than the minimum piece availability. Example: There are 10 pieces, Peer A has pieces 0 to 5, Peer B has 2 to 7, and Peer C has 4 to 9. Pieces 0, 1, 8, 9 have availability 1. Pieces 2, 3, 6, 7 have availability 2. Pieces 4 and 5 have availability 3. The entire torrent has availability 1.6 (1 + 6/10). The integer part is 1 because 1 is the lowest piece availability. The fractional part is 6/10 because more than one peer has pieces 2 to 7 (6 pieces) and there are 10 total pieces. Even though 3 peers have pieces 4 and 5, it does not further increase the availability. Sometimes "distributed copies" is considered to be "availability minus 1". So if the availability is 2.6, the distributed copies will be 1.6 because it is only counting the additional "copies" of the file.

Choked Describes a peer to which 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 because it already has all the pieces) The client is already uploading at its full capacity (it has reached the value of max_uploads) The second client has been blacklisted for being abusive or is using a blacklisted BitTorrent client.

Client The program that enables peer-to-peer file sharing via the BitTorrent protocol. See Comparison of BitTorrent clients.

Distributed Hash Table Distributed Hash Tables (DHT) are used in Bittorrent for peers to send a list of other seeds/peers in the swarm for a particular torrent directly to a client without the need for a tracker.

Encryption

The obfuscation of BitTorrent protocol headers and data, used mainly to hide the fact that BitTorrent is in use from internet service providers that might block or throttle BitTorrent traffic. Encryption does not prevent others (such as copyright holders) from seeing what a particular IP address is downloading, and it does not hide one's IP address from other members of the swarm or from the tracker.

Endgame/Endgame mode Any applied algorithm for 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 snapshot of a moment in the video, or in some cases malware).

Freeleech Freeleech means that the download size of the torrent does not count towards the user's overall ratio, though upload still does.

Grab A torrent is grabbed when its metadata files have been downloaded.

Hash The hash is a digital fingerprint in the form of a string of alphanumeric 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 "hashsum". Torrent files contain 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. 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 collision. 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 extraordinarily small.

Health Health is shown in a bar or in % usually next to the torrent's name and size on the site where the .torrent file 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). Health does not indicate whether the torrent is free of malware.

Hit-and-run To intentionally "leech" a file; downloading a file while seeding as little as possible. It's abbreviated HnR or H&R.

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.

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

Leech has two meanings. Often, leecher is synonymous with downloader: simply describing a peer or any client that does not have 100% of the data. The term leech also refers to a peer (or peers) that has a negative effect on the swarm by having a very poor share ratio, downloading much more than they upload. Leeches may be on asymmetric Internet connections or do not leave their BitTorrent client open to seed the file after their download has completed. However, some leechers intentionally avoid uploading by using modified clients or excessively limiting their upload speed.

Lurker

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.

Magnet link

A mechanism different from a .torrent metafile which can be used to identify a set of files for BitTorrent based on content, as opposed to referencing any particular tracker. The method is not limited to BitTorrent data.

Overseeded In private trackers using ratio credit, a torrent is overseeded when its availability is so high that seeders have difficulty finding downloaders.

p2p

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Glossary of BitTorrent terms

Start with the simplest possible case. Write down what Glossary of BitTorrent terms claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Glossary of BitTorrent terms before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Glossary of BitTorrent terms ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Glossary of BitTorrent terms

In research: Glossary of BitTorrent terms appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Glossary of BitTorrent terms in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Glossary of BitTorrent terms is common in secondary-school and first-year university syllabi. It links to neighbouring topics BitTorrent, Glossaries of computers, so understanding it makes those chapters shorter.
In everyday life: Look for Glossary of BitTorrent terms outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Glossary of BitTorrent terms in 20 minutes

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Frequently asked questions

What is Glossary of BitTorrent terms in simple terms?

This is a glossary of jargon related to peer-to-peer file sharing via the BitTorrent protocol. Terms Availability (Also known as distributed copies.) The availability of each piece in the torrent is defined as the number of peers who have a copy of that piece.

Why does Glossary of BitTorrent terms matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Glossary of BitTorrent terms?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Glossary of BitTorrent terms.