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The topic of BitTorrent introduces many questions. What is BitTorrent? We know it is a way to transfer files, but how does it work? Why is it better? We will be examining the underlying structure and reveal the differences from more traditional file sharing methods. BitTorrent has caused a tremendous sociological impact. The sheer popularity of Bittorrent has changed the landscape of the internet in many ways; what are they?

In this image, the bottom seed possesses the entire file, represented by the six colours. It begins by sending two pieces of the file (the red and the green) to two computers; in turn, they will pass the files to other users, while the computer with the complete file continues to send different pieces to users who have not yet received a file. Image taken from: What is BitTorrent? A Beginner's Guide

What is BitTorrent?

BitTorrent is a peer-to-peer (P2P) protocol that allows data to be transferred in a fast and inexpensive manner. BitTorrent is often used to distribute very large files as a result of its speed.[2] BitTorrents efficiency stems from distributing the bandwidth load necessary to share a file among all the peers. A successful application of BitTorrent requires users to share as much bandwidth available to them to assist in distributing the file. Users who choose not to, or throttle their uploads(limiting their maximum upload speed) slow down the process as a whole by consuming, but not contributing any bandwidth. Otherwise known as the free rider problem, it is discussed further into the article.[5]

How BitTorrent Works

Using BitTorrent begins with a file containing the .torrent extension, otherwise known as a torrent. This file contains basic information about the structure of the files being shared such as how many parts it is comprised of and an URL to the tracker. A client utilizes the data in the torrent to connect to a tracker, determines what parts of the file it requires and makes requests it. A tracker coordinates the actions of all the peers, keeps track of which user has which piece of the file, their total download and upload, and how much the user has left until the file is finished downloading. The tracker never hosts any part of the file being shared, it merely coordinates the actions of the peers hosting the file to provide it to the various users as efficiently as possible.[1]

The network of users linked together are called a swarm; this includes both peers, seeds and users who possess a complete copy of the file. Once the file finishes downloading and the user leaves the client open to allow others to continue downloading, the user is seeding the file. When there are no seeds for a torrent, all the peers will only have parts of a complete file. A seed may need to reseed by reconnecting to the swarm so peers can obtain the missing pieces. In some situations, all the parts of a file are distributed amongst the peers already. Otherwise known as a distributed copy, it means all the data necessary to download a complete the file are being shared despite the absence of a seed.[1] Another form of seeding, called Super Seeding is used when a user is the only seed in a swarm. Super Seeding changes the normal behavior of a seed to attempt to create a new seed as quickly and efficiently as possible. This maximizes efficiency by duplicating all the necessary files as quickly as possible in the event that the sole seed becomes unavailable.

BitTorrent Compared to Other Forms of File Transfer

Previous file sharing software, such as KaZaA, Morpheus and Nutella, allow a user to trade files by directly connecting to another single user using a one-on-one approach. BitTorrent allows each person to connect and share a file with multiple users downloading the file at the same time. With the one-on-one method, the download will stop and queue if the person providing the file switches off halfway through the download. On the other hand, if this happens while using BitTorrent, another user who has the other half will provide the rest of the file.[3]

The primary disadvantage with BitTorrent is that once material becomes old or obsolete, users tend to stop seeding the content. Unlike current or popular material, it can be extremely difficult to locate a seeded torrent to complete the transfer successfully.

With BitTorrent, a user receives a 'piece' or segment of a file from a different peer, until the user has collected all the pieces to create an entire file. BitTorrent allows the user to simultaneously download needed parts of the file and upload parts of the file they already have for another user. By doing this, download time is reduced because users do not have to wait for their peers to have completed torrents before receiving needed parts of the file. [4]

Real World Application

Bittorrent provides an easy way for software producers to cheaply and efficiently distribute updates to their software at a low cost. Blizzard Entertainment integrated the technology to assist in distributing software updates for their title World of Warcraft. With over 11 million subscribers, the logistical ramifications of providing free content updates are enormous. Larger content updates have been known to be as large as 340 - 500MB. With a subscriber base of 11 million, a free content patch as large as 500MB equates to over 5000 TB of data. Bittorrent provides an outlet to both distribute the update quickly by distributing the load over the entire subscriber base and gives incentive to the producer to create higher quality updates as a function of the lower cost.

Free Rider Problem

The BitTorrent protocol heavily relies on all users to contribute by sharing the pieces of a file to other users. Known as the Free Rider Problem, BitTorrent loses efficiency if a glut of users choose to throttle or completely cut off their upload. Users do this for a variety of reasons. Users may restrict downloading to maximize their available bandwidth to finish receiving the entire file faster. Many ISPs provide a relatively small upload limit compared to their download limit. As a result users may consider their upload bandwidth too valuable and save it for other uses.[5]

Several approaches have been developed to discourage Free Riding. Many popular clients such as Vuze or µTorrent restricts your maximum download speed based on your maximum upload. The effectiveness of this approach is arguable as the upload limit necessary to have unthrottled downloads are comparatively small.

Many trackers such as Demonoid require users to register before allowing them use their services. Once registered, these sites convert your bandwidth ratio in terms of a numerical ratio. For example, a share ratio of 0.5 means you have contributed half as much as you have downloaded. These sites encourage sharing by implementing rewards or penalties based on your share ratio. Penalties take the form of reduced download speeds or in extreme cases of abuse, a user may be restricted to upload only until their ratio attains a certain threshold. To contrast, a site may "reward" a high uploader by providing them access to special, higher quality, premium content largely unavailable to others.

Opponents of this system argue that their situation may severely limit the amount they can upload. Some trackers have adopted a system where a user may donate money towards the maintenance of the tracker in exchange for modifying their share ratio. For example, a tracker may remove 1 gigabyte of downloaded data from your download ratio for every dollar donated.

Sociological Impact

Growth of BitTorrent

The Pirate Bay is the world’s largest torrent tracker on the web today. This Swedish-based website was established to promote the free sharing of intellectual property. It has also become known as one of the largest facilitators of piracy and illegal downloading.

In December 2006, The Pirate Bay had 576,080 torrents and 4,274,698 peers, and these numbers were nearly doubled by December 2007. In November 2008, the website announced its record of 25 million peers [6]. These large statistics indicate that the BitTorrent protocol is becoming astoundingly popular.

Effect of P2P on Business

Prior to the advent of efficient file sharing methods such as Napster, Kazaa or BitTorrent, the entertainment industry largely ignored the internet as a distribution medium. Prior methods such as IRC, News Groups and FTP servers are comparatively very difficult to use to the average user. It can be argued that without the overwhelming popularity of services such as Napster or Kazaa, the entertainment industry would be severely lagging behind on incorporating online sales into their business model. For example, the concept behind iTunes is extremely similar to service Napster provides. Without the existence of Napster, it would be unknown how much of a market exists for the iTunes business model. The risk may have been too great to model a project such as iTunes without any points of comparison.


BitTorrent was originally designed for legal file transfers, and contrary to popular belief the protocol itself is not illegal. BitTorrent websites do not host any of the files, regardless of legality. They simply have a link to a torrent file, which has information hosted by the seeders. Some of these files can be illegal or copyrighted material, such as music and movie files. Because of this, the Recording Industry Association of America (RIAA) and Motion Picture Association of America (MPAA) regard BitTorrent as a means for piracy, and see the development and popularity of the protocol as detrimental to their industry, claiming that they lose money from movie and album sales due to piracy. [7]

Although the MPAA and RIAA resist the revolution towards BitTorrent, the protocol is not condemned by all in the entertainment industry. In fact, many recording artists take advantage of this technology to distribute their music to their fans. The band Nine Inch Nails used The Pirate Bay in 2007 to release three of their tracks [8]. Other bands such as Death Cab for Cutie, The Postal Service, and Cursive have released songs or samples of songs on BitTorrent for free download.[9] By distributing their tracks through BitTorrent, these artists are promoting their album, which may lead to an increased interest in their albums, or may attract potential fans. In this way, BitTorrent is also a useful medium for independent filmmakers and recording artists, who have a smaller promotional budget to market their work.

Deceptive Statistics

Two statistics have been brought up repeatedly when it comes to the impact that peer-to-peer and BitTorrent has had on intellectual property policy in the United States: 750,000 jobs lost due to intellectual property theft and $200 - $250 billion for the cost of IP infringement to the economy. According to an investigation by Ars Technica, these two statistics are unsubstantiated. The first number originates from 1986, when the number of jobs lost due to counterfeiting was estimated to be in the broad range of 130,000 to 750,000. The $200 - $250 billion digit was found as far back as 1993 in an issue of Forbes magazine, and was not used an estimate of the cost to the U.S. economy of IP piracy, but as a number found in a claim that "counterfeit goods” was a global market worth $200 billion.[10]

Network Neutrality

Network Neutrality is the principle that states that all internet activity should be treated equally, users should have freedom to use their bandwidth however they prefer [11]. Net Neutrality is the philosophy that freedom of choice is paramount and an Internet Service Provider (ISP) should not limit or restrict usage to the internet. In 2007, Comcast, one of the largest ISPs in the United States, attempted to disrupt the amount of bandwidth available to peer-to-peer applications. ISPs have been preventing BitTorrent users from seeding files justifying it by claiming that it is unfair for other customers who share bandwidth with BitTorrent power users [12]. The popularity and the large bandwidth consumption BitTorrent has exasperated Network Neutrality.


1. http://www.dessent.net/btfaq/#what

2. http://www.bittorrent.com/btusers/help/faq/bittorrent-concepts

3. http://www.flarefire.com/learn_bittorrent/index.html

4. http://qntm.org/?bittorrent

5. http://research.microsoft.com/workshops/IPTPS2007/papers/SirivianosParkChenYang.pdf

6. http://www.techradar.com/news/internet/web/pirate-bay-bigger-than-all-of-scandinavia-485542

7. http://www.wisegeek.com/what-are-torrents.htm

8. http://www.slyck.com/story1461.html

9. http://torrentfreak.com/bittorrent-an-excellent-medium-for-indie-labels/

10. http://arstechnica.com/articles/culture/dodgy-digits-behind-the-war-on-piracy.ars/1

11. http://www.google.com/help/netneutrality.html

12. http://torrentfreak.com/comcast-throttles-bittorrent-traffic-seeding-impossible/