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Bit torrent documentation

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  • 1. Bit Torrent 1. INTRODUCTION Bit Torrent is a peer-to-peer file sharing protocol used for distributing large amounts of data. Bit Torrent is one of the most common protocols for transferring large files, and it has been estimated that it accounts for approximately 27-55% of all Internet traffic as of February 2009. Bit Torrent protocol allows users to distribute large amounts of data without putting the level of strain on their computers that would be needed for standard Internet hosting. A standard host's servers can easily be brought to a halt if extreme levels of simultaneous data flow are reached. The protocol works as an alternative data distribution method that makes even small computers (e.g. mobile phones) with low bandwidth capable of participating in large data transfers. First, a user playing the role of file-provider makes a file available to the network. This first user's file is called a seed and its availability on the network allows other users, called peers, to connect and begin to download the seed file. As new peers connect to the network and request the same file, their computer receives a different piece of the data from the seed. Once multiple peers have multiple pieces of the seed, Bit Torrent allows each to become a source for that portion of the file. The effect of this is to take on a small part of the task and relieve the initial user, distributing the file download task among the seed and many peers. With Bit Torrent, no one computer needs to supply data in quantities which could jeopardize the task by overwhelming all resources, yet the same final result each peer eventually receiving the entire file is still reached. After the file is successfully and completely downloaded by a given peer, the peer is able to shift roles and become an additional seed, helping the remaining peers to receive the entire file. This eventual shift from peers to seeders determines the overall 'health' of the file. This distributed nature of Bit Torrent leads to a flood like spreading of a file throughout peers. As more peers join the swarm, the likelihood of a successful download increases. Relative to standard Internet hosting, this provides a significant reduction in the A.Jagadeesh Page 1
  • 2. Bit Torrent original distributor's hardware and bandwidth resource costs. It also provides redundancy against system problems, reduces dependence on the original distributor and provides a source for the file which is generally temporary and therefore harder to trace than when provided by the enduring availability of a host in standard file distribution techniques. 2. HISTORY Bit Torrent, Inc., headquartered in San Francisco, California is an American corporation that develops peer-assisted Internet content delivery technology based on the Bit Torrent protocol. Bram Cohen is the creator of Bit Torrent, which is now one of the most successful peer-to-peer programs ever. Cohen suffers from Asperser’s syndrome, which gives him a concentration level far surpassing the normal person, but makes it hard for him to relate to other people. This helps him to solve difficult algorithms, and makes him one of the best programmers in the world. His program, Bit Torrent, accounts for more than one third of all internet traffic according to analysts at Cache logic, an Internet-traffic analysis firm in Cambridge, England. Cohen first showed his code for the program at a hacker conference in 2002, so that geeks could use the program to swap Linux software online cheaply and quickly. However the first beta version on the program was shared over the internet in 2001. Today over 20 million people have downloaded Bit Torrent. A large majority of these users use the program for downloading TV shows and movies instead of Linux though. Bit Torrents popularity has gone up exponentially in the past couple years, and if it continues in this path over 40 million people will use the program in 2006. Bram Cohen and his family now live off donations that people give him for the program. The company offers popular consumer freeware (the Bit Torrent client). The company also licenses its technology, called Bit Torrent DNA (Delivery Network Accelerator), to websites "to add the speed and efficiency of patented Bit Torrent technology to their current content delivery infrastructure, significantly reducing bandwidth costs while increasing capacity over standard HTTP delivery solutions." The third product offering is A.Jagadeesh Page 2
  • 3. Bit Torrent the Bit Torrent Software Development Kit (SDK) for consumer electronics and home networking hardware manufacturers. Bit Torrent DNA allows website developers to overlay their content delivery network (CDN) vendor with Bit Torrent's P2P CDN, built on the company's widely used client software. One should be able to expect dramatic cost savings using P2P bandwidth relative to the cost of CDN bandwidth; however ISPs may view this as an unattractive application of their network capacity. The Bit Torrent SDK (or what the company calls "Bit Torrent Certified" program) offers compatibility between hardware, such as Network Attached Storage (NAS) solutions and other Internet-enabled devices, and the Bit Torrent client. 3. Bit Torrent DNA a. Purpose This program is designed to speed up the viewing of streaming video, downloading software (with or without the Bit Torrent protocol) and playing online video games. It does so by distributing the end users' downloads between each other. In this way, the developers intend that content providers should take less load on their servers so the end users can receive the content faster. b. Protocol Bit Torrent DNA is different from traditional Bit Torrent in that it relies on publisher HTTP servers in order to provide publishers with guaranteed minimum data delivery rate, as well as give publishers control over content delivery (peers must connect to the origin server before they can reach other peers), and collect information about content delivery to share with the publisher. The quality of the file transfer is specified in terms of a long-term average bitrates for data and in terms of meeting deadlines when streaming. It also can give bandwidth to TCP and other traffic. A.Jagadeesh Page 3
  • 4. Bit Torrent DNA is also different from traditional Bit Torrent in that it is a UDP-based protocol that has replaced regular TCP-based bandwidth throttling with a much more sensitive bandwidth management technique. c. Relation to the official Bit Torrent client Apart from being installed by third party websites and software companies, the program for end users is also installed when the official Bit Torrent client is installed (starting with the rebranded version 6.0). However, it can be independently uninstalled. The first version of the DNA made it possible to keep the DNA application installed and yet temporarily stopped until the next system restart (through the system's control panel, in Windows XP). The DNA GUI was completely removed in the official Bit Torrent version 6.1 and 6.1.1, but was re-introduced in version 6.1.2. d. History Since October, 2007 Bit Torrent DNA has been offered by Bit Torrent, Inc. as a commercial service that content providers can purchase (for an undisclosed price) and as a free background program for end users. Company President Ashwin Navin launched the product claiming that "Implementing Bit Torrent DNA on top of legacy infrastructure has the profound impact of allowing our customers to deliver a better user experience. Higher quality video, faster software downloads, all with the security and reliability of a managed service." Navin in a podcast interview claimed that he attempted to sell Bit Torrent DNA in January 2005. After finding that Bit Torrent's brand was too polarizing for potential customers, they delayed the launch until after partnering with nearly 50 media companies in the Bit Torrent Entertainment Network. That provided the company enough public validation to finally launch Bit Torrent DNA two and half years later. A.Jagadeesh Page 4
  • 5. Bit Torrent The service's first customer was the company Bright cove that chose to use it to distribute streaming video files. As of May 2009, the Asus support website is using Bit Torrent DNA as an additional download method of their larger files in addition to their multiple somewhat internationally distributed HTTP servers and content delivery mirrors and other redirection facilities Asus has been known to rely in the present and past for their data delivery needs. Currently, a separate "P2P" icon is being presented for the DNA style downloads next to the "Global" and "Chinese" located servers as an example. 4. What is Bit Torrent? Bit Torrent is a protocol designed for transferring files. It is peer-to-peer in nature, as users connect to each other directly to send and receive portions of the file. However, there is a central server (called a tracker) which coordinates the action of all such peers. The tracker only manages connections, it does not have any knowledge of the contents of the files being distributed, and therefore a large number of users can be supported with relatively limited tracker bandwidth. The key philosophy of Bit Torrent is that users should upload (transmit outbound) at the same time they are downloading (receiving inbound.) In this manner, network bandwidth is utilized as efficiently as possible. Bit Torrent is designed to work better as the number of people interested in a certain file increases, in contrast to other file transfer protocols. One analogy to describe this process might be to visualize a group of people sitting at a table. Each person at the table can both talk and listen to any other person at the table. These people are each trying to get a complete copy of a book. Person A announces that he has pages 1-10, 23, 42-50, and 75. Persons C, D, and E are each missing some of those pages that A has, and so they coordinate such that A gives them each copies of the pages he has that they are missing. Person B then announces that she has pages 11-22, 31-37, and 63-70. Persons A, D, and E tell B they would like some of her pages, so she gives them copies of the pages that she has. The process continues around the table until everyone has announced what they have (and hence what they are missing.) The people at A.Jagadeesh Page 5
  • 6. Bit Torrent the table coordinate to swap parts of this book until everyone has everything. There is also another person at the table, who we'll call 'S'. This person has a complete copy of the book, and so doesn't need anything sent to him. He responds with pages that no one else in the group has. At first, when everyone has just arrived, they all must talk to him to get their first set of pages. However, the people are smart enough to not all get the same pages from him. After a short while they all have most of the book amongst themselves, even if no one person has the whole thing. In this manner, this one person can share a book that he has with many other people, without having to give a full copy to everyone that's interested. He can instead give out different parts to different people, and they will be able to share it amongst themselves. This person who we've referred to as 'S' is called a seed in the terminology of Bit Torrent. There's more about the various terms in a later section 5. Peer-to-peer File Sharing Peer-to-peer file sharing is different from traditional file downloading. In peer-to- peer sharing, you use a software program to locate computers that have the file you want. Because these are ordinary computers like yours, as opposed to servers, they are called peers. The process works like this: • You run peer-to-peer file-sharing software (for example, a Gnutella program) on your computer and send out a request for the file you want to download. • To locate the file, the software queries other computers that are connected to the Internet and running the file-sharing software. • When the software finds a computer that has the file you want on its hard drive, the download begins. • Others using the file-sharing software can obtain files they want from your computer's hard drive. A.Jagadeesh Page 6
  • 7. Bit Torrent The file-transfer load is distributed between the computers exchanging files, but file searches and transfers from your computer to others can cause bottlenecks. Some people download files and immediately disconnect without allowing others to obtain files from their system, which is called leeching. This limits the number of computers the software can search for the requested file. 6. Bit Torrent Terminology a. Torrent A small metadata file which contains information about the data you want to download, not the data itself. It is downloaded from a web site (Bit Torrent file extension is .torrent) by clicking on a download link. It can also be saved to your computer. This is useful if you want to be able to re-open the Torrent later on without having to find the link again. b. Peer A peer is another computer on the internet that is sharing the file you wish to download. Typically a peer does not have the complete file. If it did it would be called a A.Jagadeesh Page 7
  • 8. Bit Torrent seed. Peers are also called leeches, to distinguish them from those who have completed their download and continue to leave their Bit Torrent client running and act as a seed. c. Seeder A computer that has a complete copy of the specific Torrent you are downloading. Once your client finishes downloading, it will remain open until you click the Finish button. This is known as seeding. You can also start a Bit Torrent client with a complete file, and once Bit Torrent has checked the file it will connect and seed the file to others. It is good to continue seeding a file after you have finished downloading, to help others finish. Also, when a new torrent is posted to a tracker, someone must seed it in order for it to be available to others. The tracker doesn't know anything of the actual contents of a file, so it's important to follow through and seed a file if you upload the Torrent to a tracker. d. Swarm The group of users that are collectively connected for a particular file. Example, if you start a Bit Torrent client and it tells you that you're connected to 5 peers and 1 seeds, then the swarm consists of you and those 6 other people. e. Tracker Server on the Internet that coordinates the action of bit Torrent clients. Upon opening a torrent, you contact the tracker and receive a list of peers to connect to. Throughout the transfer, your computer will query the tracker, telling it how much you've downloaded and uploaded and how much before finishing. If a tracker is down and you try to open a torrent, you will be unable to connect. If a tracker goes down during a torrent (you have already connected at some point and are already talking to peers), you will be able to continue transferring with those peers, but no new peers will be able to contact you. Tracker errors are often temporary, leave the client open and continue trying. A.Jagadeesh Page 8
  • 9. Bit Torrent f. Leeches They are similar to peers in that they won’t have the complete file. But the main difference between the two is that a leech will not upload once the file is downloaded. 7. The architecture of Bit Torrent The Bit Torrent protocol can be split into the following five main components: 1. Meta-info file –a file which contains details necessary for the protocol to operate. 2. Tracker- a server which helps manages the Bit Torrent protocol. 3. Peers- users exchanging data via Bit Torrent protocol. 4. Data- the files being transferred across the protocol. 5. Client-the program which sits on a peer’s computer and implements the protocol. 8. Meta-info file When someone wants to publish data using the Bit Torrent protocol, they must create a meta-info file. This file is specific to the data they are publishing, and contains all the information about a torrent, such as the data to be included, and IP address of the tracker to connect to. A tracker is a server which 'manages' a torrent, and is discussed in the next section. The file is given a '.torrent' extension, and the data is extracted from the file by a Bit Torrent client. This is a program which runs on the user computer, and implements the bit torrent protocol. Every meta-info file must contain the following information, (or 'keys'): A.Jagadeesh Page 9
  • 10. Bit Torrent • Info: A dictionary which describes the file(s) of the torrent. Either for the single file, or the directory structure for more files. Hashes for every data piece, in SHA 1 format are stored here. • announce: The announce URL of the tracker as a string • Announce-list: Used to list backup trackers • Creation date: The creation time of the torrent by way of UNIX time stamp (integer seconds since 1-Jan-1970 00:00:00 UTC) • Comment: Any comments by the author • Created by: Name and Version of program used to create the meta-info file. 9. Tracker A tracker is used to manage users participating in a torrent (know as peers). It stored statistics about the torrent, but its main role is allow peers to 'find each other' and start communication, i.e. to find peers with the data they require. Peers know nothing of each other until a response is received from the tracker. Whenever a peer contacts the tracker, it reports which pieces of a file they have. That way, when another peer queries the tracker, it can provide a random list of peers who are participating in the torrent, and have the required piece. A tracker is a HTTP/HTTPS service and typically works on port 6969. The address of the tracker managing a torrent is specified in the meta-info file, a single tracker can manage multiple torrents. Multiple trackers can also be specified, as backups, which are handled by the Bit Torrent client running on the user’s computer. Bit Torrent clients communicate with the tracker using HTTP GET requests, which is a standard CGI method. This consists of appending a "?" to the URL, and separating parameters with a "&". The parameters accepted by the tracker are: • Info hash: 20-byte SHA1 hash of the info key from the meta-info file. • Peer id: 20-byte string used as a unique ID for the client. A.Jagadeesh Page 10
  • 11. Bit Torrent • Port: The port number the client is listed on. • Uploaded: The total amount uploaded since the client sent the 'started' event to the tracker in base ten ASCII. • Downloaded: The total amount downloaded since the client sent the 'started' event to the tracker in base ten ASCII. • Left: The number of bytes the client till has to download, in base ten ASCII. • Ip: (optional) The IP address of the client machine, in dotted format. 10.What Bit Torrent Does? Unlike some other peer-to-peer downloading methods, Bit Torrent is a protocol that offloads some of the file tracking work to a central server (called a tracker). Another difference is that it uses a principal called tit-for-tat. This means that in order to receive files, you have to give them. This solves the problem of leeching -- one of developer Bram Cohen's primary goals. With Bit Torrent, the more files you share with others, the faster your downloads are. Finally, to make better use of available Internet bandwidth (the pipeline for data transmission), Bit Torrent downloads different pieces of the file you want simultaneously from multiple computers You open a Web page and click on a link for the file you want. Bit Torrent client software communicates with a tracker to find other computers running Bit Torrent that have the complete file (seed computers) and those with a portion of the file (peers that are usually in the process of downloading the file). The tracker identifies the swarm, which is the connected computers that have all of or a portion of the file and is in the process of sending or receiving it. The tracker helps the client software trade pieces of the file you want with other computers in the swarm. Your computer receives multiple pieces of the file simultaneously. If you continue to run the Bit Torrent client software after your download is complete, others can receive .torrent files A.Jagadeesh Page 11
  • 12. Bit Torrent from your computer; your future download rates improve because you are ranked higher in the "tit-for-tat" system. Downloading pieces of the file at the same time helps solve a common problem with other peer-to-peer download methods: Peers upload at a much slower rate than they download. By downloading multiple pieces at the same time, the overall speed is greatly improved. The more computers involved in the swarm, the faster the file transfer occurs because there are more sources of each piece of the file. For this reason, Bit Torrent is especially useful for large, popular files 11.Creating and publishing Torrents A.Jagadeesh Page 12
  • 13. Bit Torrent The peer distributing a data file treats the file as a number of identically sized pieces, typically between 32 KB and 4 MB each. The peer creates a checksum for each piece, using the SHA1 ha shing algorithm, and records it in the Torrent file. Pieces with sizes greater than 512 KB will reduce the size of a torrent file for a very large payload, but is claimed to reduce the efficiency of the protocol. When another peer later receives a particular piece, the checksum of the piece is compared to the recorded checksum to test that the piece is error-free. Peers that provide a complete file are called seeders, and the peer providing the initial copy is called the initial seeder. The exact information contained in the Torrent file depends on the version of the Bit Torrent protocol. By convention, the name of a torrent file has the suffix .torrent. Torrent files have an "announce" section, which specifies the URL of the tracker, and an "info" section, containing (suggested) names for the files, their lengths, the piece length used, and a SHA-1 hash code for each piece, all of which are used by clients to verify the integrity of the data they receive. Torrent files are typically published on websites or elsewhere, and registered with at least one tracker. The tracker maintains lists of the clients currently participating in the torrent. Alternatively, in a tracker less system (decentralized tracking) every peer acts as a tracker. Azures were the first Bit Torrent client to implement such a system through the distributed hash table (DHT) method. An alternative and incompatible DHT system, known as Mainline DHT, was later developed and adopted by the Bit Torrent (Mainline), µTorrent, Transmission, r Torrent, K Torrent, Bit Comet, and Deluge clients. After the DHT was adopted, a "private" flag—analogous to the broadcast flag—was unofficially introduced, telling clients to restrict the use of decentralized tracking regardless of the user's desires. The flag is intentionally placed in the info section of the Torrent so that it cannot be disabled or removed without changing the identity of the torrent. The purpose of the flag is to prevent torrents from being shared with clients that do not have access to the tracker. The flag was requested for inclusion in the official specification in August, 2008, A.Jagadeesh Page 13
  • 14. Bit Torrent but has not been accepted. Clients that have ignored the private flag were banned by many trackers, discouraging the practice. 12.Downloading Torrents and sharing files Users browse the web to find a torrent of interest, download it, and open it with a Bit Torrent client. The client connects to the tracker(s) specified in the Torrent file, from which it receives a list of peers currently transferring pieces of the file(s) specified in the Torrent. The client connects to those peers to obtain the various pieces. If the swarm contains only the initial seeder, the client connects directly to it and begins to request pieces. Clients incorporate mechanisms to optimize their download and upload rates; for example they download pieces in a random order to increase the opportunity to exchange data, which is only possible if two peers have different pieces of the file. The effectiveness of this data exchange depends largely on the policies that clients use to determine to whom to send data. Clients may prefer to send data to peers that send data back to them (a tit for tat scheme), which encourages fair trading. But strict policies often result in suboptimal situations, such as when newly joined peers are unable to receive any data because they don't have any pieces yet to trade themselves or when two peers with a good connection between them do not exchange data simply because neither of them takes the initiative. To counter these effects, the official Bit Torrent client program uses a mechanism called “optimistic unchoking” ,whereby the client reserves a portion of its available bandwidth for sending pieces to random peers (not necessarily known good partners, so called preferred peers) in hopes of discovering even better partners and to ensure that newcomers get a chance to join the swarm. The community of Bit Torrent users frowns upon the practice of disconnecting from the network immediately upon success of a file download, and encourages remaining as another seed for as long as practical, which may be days. A.Jagadeesh Page 14
  • 15. Bit Torrent 13.Advantages Virtually every computer program has its advantages and disadvantages, and Bit Torrent is no exception. The fact that there are disadvantages to using Bit Torrent does not mean that the program or its system is defective; it simply proves that man created it. One should always consider the advantage or disadvantage to using a new program to ensure there are not too many surprises along the duration of use. Should the advantages to using the program outweigh the disadvantages, than it can be determined that the program is suitable for use. The simplicity of Bit Torrent is a major advantage. The downloading software is simple, and small in size. All one needs to do is retrieve the downloading software and save it on to a computer. Then next simple step is surfing the internet’s numerous Torrent sites. You can select a file to download, and it is saved onto the computer’s hard drive. Another advantage is that the files on these websites, although quite large, can be downloaded twice as fast. This is because the structuring of the Bit Torrent system creates multiple hosts or “seeders” that a file can be downloaded from. Instead of downloading a file from a single source, which could encounter slow or disabled connections, it is downloaded from multiple sources. This allows Bit Torrent users to download a large file in hours, compared to days. The integrity of torrent files poses another advantage. Torrent files include a hash system, which prevents tampered or broken files from being shared. This feature is attractive to many downloader’s who are sick of half or whole files being scrambled and ultimately useless. The quality of Torrent files is surprising. One could download a movie, and it would be of the same quality of movies shown in theatres. Another advantage of the Bit Torrent program is that it helps individuals, or “up and comers”, to quickly deliver new music, movies, and software to the public. Uploading files is just as easy as downloading, and the best part is that it’s all free. For A.Jagadeesh Page 15
  • 16. Bit Torrent those who can’t afford to advertise their product, Bit Torrent is an excellent resource to help get people off their feet. 14.Disadvantages As with every other program, Bit Torrent has some disadvantages. The emphasis put into the simplicity of Bit Torrent resulted in a lack of features for the program. Many other P2P programs have search engines, a file library, and other features to make the program more users friendly. However, the publishers of Bit Torrent software are constantly coming out with new upgrades that give the system more features. Bit Torrent users must refer to surfing the web for their files, and many don’t have a problem with this. However, some reports have been made about a few Torrent sites occasionally stopping a file download to request the downloader to find a new seed. This, although rare, is a problem with the Bit Torrent download process. When many run the Bit Torrent software they discover another flaw. Some computers have smaller processors, meaning that when the Bit Torrent software is running the computer performance may drop drastically. This is because the program is designed to use more computer cycles in order to download files quicker. One may also run into problems downloading if their computer has a firewall. Bit Torrent requires multiple ports needing to be used in order to speed up the downloads, a firewall may block some of these ports. The result would simply be a slower download rate. The last disadvantage to using Bit Torrent is one that every P2P software user encounters, the legal issues. Although not condoned by its creator, Bit Torrent can be used to traffic pirated files. Some ISP’s have been notified by law enforcement that they must shut down their operation. In some cases, people have been arrested and sent to jail. The nicer part about Bit Torrent is that is makes it more difficult for investigators to track down individual users who may be breaking a few laws. The overall result should show that the advantages to using Bit Torrent outweigh the disadvantages; however this result may differ among individuals. The small A.Jagadeesh Page 16
  • 17. Bit Torrent disadvantages of using this program are simply a minor side effect of the greater advantages to users. Bit Torrent creates an opportunity for more people to share larger files with simplicity and speed. The new technology invented by Bram Cohen, creator of Bit Torrent, allows users to download and upload files through each other instead of from one source. This makes Bit Torrent above all the rest. 15.Legal Issues The technology that allows P2P file sharing while saving bandwidth is the bit Torrent protocol and it is legal. However downloading and sharing or otherwise disseminating copyrighted material is illegal and several legal actions may be taken against anyone who does this. Residents of Canada and, as of February 2006, France are an exception. They are currently protected from certain P2P copyright legal actions. What has happened recently is that the MPAA (Motion Picture Association of America) and RIAA (Recording Industry Association of America) together with governments of England and Australia have filed class action lawsuits in the civil courts. The lawsuits are based upon copyright infringement and ask for thousands of dollars in penalties. Your internet service provider may release their internet logs, which show your downloading activity. Using that information the MPAA or RIAA may investigate you or file an action against you. Or include you in a class action lawsuit. Another legal issue commonly brought up when talking about peer-to-peer sharing is the idea of fair use. A good example of fair use is taping a show on your VCR. You have copied a copyrighted material, but since you are using it for your own personal use and won’t distribute or make money off of it, it is legal. There are many out there who believe the distribution of digital files should fall under fair use, they argue that it is the same as inviting a friend over to watch a DVD or listen to music. On November 23, 2005, the Motion Picture Association of America and Bit Torrent Inc. CEO Bram Cohen, signed a deal they hoped would reduce the number of unlicensed A.Jagadeesh Page 17
  • 18. Bit Torrent copies available through bit Torrent.com's search engine, run by Bit Torrent, Inc. It meant Bit Torrent.com had to remove any links to unlicensed copies of films made by seven of Hollywood's major movie studios. As it covered only the BitTorrent.com website, it is unclear what overall effect this has had on copyright infringement. The same evolution has happened with the internet. Slowly more and more people now have access to it making it possible for them to get whatever they want whenever they want due to digitization. Music, movies, television programs all can be shared and copied across the world using a broadband connection. 16.Bit Torrent (software) Bit Torrent is a peer-to-peer program developed by Bram Cohen and Bit Torrent, Inc. used for uploading and downloading files via the Bit Torrent protocol. Bit Torrent was the first client written for the protocol. It is often nicknamed Mainline by developers denoting its official origins. Since version 6.0 the Bit Torrent client has been a rebranded version of µTorrent. As a result it is no longer open source and is currently only available for Windows and Mac OS X 10.5.x. a. History Version 4.20 of the client was dubbed Allegro by Bit Torrent Inc., in reference to protocol extensions developed by the company to accelerate download performance and ISP manageability. Since version 6.0 the Bit Torrent client has been a rebranded version of µTorrent. As a result, it is no longer open source, and this version of the program is now only available for Windows and Mac OS X 10.5.x. Prior to version 6.0, Bit Torrent was written in Python, and was free software. The source code for versions 4.x and 5.x was released under the Bit Torrent Open Source License, a modified version of the Jabber Open Source License. Versions up to and A.Jagadeesh Page 18
  • 19. Bit Torrent including 3.4.2 were distributed under the MIT license. Version 5.3 and version 4.0 were relicensed under the GPL. b. Features The Bit Torrent client enables a user to search for and download torrent files using a built-in search box ("Search for torrents") in the main window, which opens the Bit Torrent search engine page with the search results in the user's default web browser. The current client includes a range of features, including multiple parallel downloads. Bit Torrent has several statistical, tabular and graphical views that allow a user to see what events are happening in the background. A host of views offer information on the peers and seeds to which the user is connected, including how much data is being downloaded from each and to how much data is being uploaded by each. It has an automatic recovery system that checks all data that has been handled after an improper shutdown. It also intermediates peering between itself, source file servers ("trackers") and other clients, thereby yielding distribution efficiencies. The client also enables users to create and share torrent files. A.Jagadeesh Page 19
  • 20. Bit Torrent 17.Concluson Bit torrent pioneered mesh-based file distribution that effectively utilizes all the uplinks of participating nodes. Most follow-on research used similar distributed and randomized algorithms for peer and piece selection, but with different emphasis or twists. This work takes a different approach to the mesh-based file distribution problem by considering it as a scheduling problem, and strives to derive an optimal schedule that could minimize the total elapsed time. By comparing the total elapsed time of Bit Torrent and CSFD in a wide variety of scenarios, we are able to determine how close Bit Torrent is to the theoretical optimum, In addition, the study of applicability of Bit Torrent to real-time media streaming application, shows that with minor modifications, Bit Torrent can serve an effective media streaming tool as well. Bit Torrent’s application in this information sharing age is almost priceless. However, it is still not perfected as it is still prone malicious attacks and acts of misuse. Moreover, the lifespan of each torrent is still not satisfactory, which means that the length of file distribution can only survive for a limited period of time. Thus, further analysis and a more thorough study in the protocol will enable one to discover more ways to improve it. A.Jagadeesh Page 20
  • 21. Bit Torrent 18.References 1. http://www.bittorrent.com 2. http://www.wikipedia.org/bittorrent 3. http://computer.howstuffworks.com/bittorrent.htm 4. http://www.bittorrent.org 5. http://www.scribd.com/doc/528983/Bittorrent-Protocol-Specification-v10 6. http://www.scribd.com/doc/15618278/The-Big-Book-of-Bit-Torrent A.Jagadeesh Page 21

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