BitTorrent
BitTorrent (of bits ( the smallest unit of data ) and english torrent, torrent 'or' torrent ', from Latin torrens ) is a collaborative file sharing protocol that is particularly suitable for the rapid distribution of large amounts of data. Unlike other file sharing techniques BitTorrent does not rely on a comprehensive file-sharing network, but builds for each file on a separate distribution.
- 3.1 Application in practice
- 4.1 Legal
BitTorrent technology
Technically, the protocol of the OSI layer 7, that is, the application layer, and is assigned to the TCP / IP reference model. The reference implementation ( BitTorrent client) by the inventor Bram Cohen was originally in the Python programming language. Today it provides a number of alternative programs available that implement the BitTorrent protocol.
Compared to conventional download a file via HTTP or FTP the ( otherwise unused ) upload capacity Downloader co-used with the BitTorrent technology, even if they have not yet fully downloaded the file. So files are not only distributed from a server, but also from user to user (peer -to-peer or P2P) passed. The less load on the server and the provider saves money. Overall, the download load is not less, it just shifts to the individual user. For popular files, this technique prevents the collapse of the network as a result of exceeding the capacity limits of the provider.
Function
In order to participate in the distribution of the data to the torrent, the client a torrent file commonly used (file name extension. Torrent or. Sector ). This is the IP address ( or host name ) of the tracker and file name, size, and a list of checksums of segments of the data to be downloaded (one or more files). Torrent files can be created with many available Bittorrent clients. Here, the initial seeding -peer ( engl. " seeder " = drill ) must establish the link to be offered as a torrent file and keep it available.
For finding other ( on a specific file interested ) peers, there are now several other options in addition to a system in which special (web) servers - the trackers (English " track" = stalk ) - the contact is mediated. The tracker maintains normally only a unique ID of the torrent locally before, are assigned the IP addresses of the peers that hold the file is available. Peers take quite common to connect to the tracker in order to react quickly to changes in the available peers can.
Torrents are usually a few dozen kilobytes in size and will be provided on the Website or through index sites (for example, The Pirate Bay, Mininova and isoHunt ) to download. Without tracker other methods must be used to locate remote sites (DHT, PEX, ... ), or it can only be exchanged with already known peers.
The client software receives from the tracker a list of peers that have data or any part thereof or are interested. Once a peer has a segment (English " chunk" ) of the file and the checksum verified, it reports this to the tracker and can file this piece now been passed on to the other peers. The set of all peers that are interested in the same torrent, called Swarm. Peers who are in possession of the complete contents of the torrents, and thus nothing to download from other clients, but only distribute data, called seeding (of English to seed. Sow ). As leechers (of English leech. Leeches; cleaner ) peers are usually referred to, which do not yet have the whole torrent content and even download more segments. ( Mainly in other contexts, they are also partly peers referred pejoratively as " leechers ", the download only, without even redistribute already downloaded segments and so the P2P principle violate. ) Generally refers to a peer associated with a client to another client.
Unlike other well-known file-sharing systems, not any files held by the participants to be replaced. Rather, each swarm distributes only the files that have been explicitly provided for download the author of the torrent file. Also, the operator of the tracker who decides which downloads to be managed by this. The individual trackers are not mutually connected, so there exists no common network, but a separate for each torrent. Thus, providers can also dissociate more easily from strangers, possibly illegal content.
Official Protocol Extensions
The evolution of the BitTorrent protocol has been handed over to the community. In the BitTorrent Enhancement Proposals (BEP ) new features that were introduced in the rule of the authors of various BitTorrent software and now standardized it will gather.
Extension for Peers to transfer metadata
The extension described in BEP 9 allows peers transmitting metadata to resolve magnet links, for example, can. In addition, a peer can without one. Torrent file to download a torrent and join to the corresponding swarm.
DHT Protocol
BEP 5 describes the use of a distributed hash table (English " Distributed Hash Table "; DHT ) based on Kademlia algorithm " tracker -less " for the (English " Trackerless " ) operation. This extension is still in draft form, the use is, however, already widely. The tracker function is assumed by the client software. This avoids some of the previous problems (for example, the lack of reliability of the tracker ), even if tracker -based operation will be possible. It also facilitates the offering, since Tracker represent the most elaborate part in BitTorrent. Since published in the November 2005 version 4.2.0 of the reference client supports the tracker -less operation, relying on the Kademlia algorithm. The tracker has a distributed basis, similar to be stored and managed as a distributed hash table on the clients themselves, as in the Kademlia network.
Modern BitTorrent clients can not do without the tracker and are decentralized ( " trackerlos "). However, they still use different protocols, enabling communication between different clients on DHT - base is not always possible. Among each other compatible are currently BitComet, Deluge, uTorrent, KTorrent, qBittorrent, rtorrent, transmission and the reference client. The developers increasingly work to establish compatibility.
UDP tracker protocol
With the expansion of BEP 15 a tracker can be queried via UDP, which can greatly reduce the volume of traffic on the tracker. This extension is still in the draft stage.
Superseeding
BEP 16 describes the so-called Superseeding ( in uTorrent also initial seeding called ), in which for the case that the respective peer the only seed in a still dataless swarm is, the shipping is optimized in this, that in the rest of Swarm as soon as possible a (distributed ) copy of the data is created. To this end, the seed is in this mode in the swarm as incomplete source and its parts are only gradually out. It provides for the time being of each part only once each and will unlock extra parts when he has received feedback that an uploaded part became more widespread. He tries to find out which peers provide for the fastest proliferation and uploads to these preferred. The client BitComet has become known to abuse this approach to their own advantage.
Superseeding was introduced in the client BitTornado. The extension is currently still in the design stage.
HTTP / FTP Seeding
BEP 17 and 19 describe methods for using HTTP or FTP web servers as complete sources (seeds) in a BitTorrent swarm.
See Article Webseed
Private Torrents
In contrast to the normal case, the public torrents, torrents of private access is restricted. With a flag in the. Torrent file (which in this case contains only a single tracker) is required by the client to be limited in finding sources to the one specified in the file tracker and only connect to clients that provides this.
BEP 27 ( still in draft ) describes the procedure.
Announce and discovery of peers using Zeroconf
With the BEP in 26 ( still in draft ) described enlargement can be found using DNS Service Discovery ( Zeroconf ) in a local network peers. Within a local network significantly higher transmission rates are usually possible and the effort required for the transmission of low. With this extension, peers can in the same local network that are interested in the same torrent, now take advantage of this relief for the swarm and the common external connection and can more peers may be found. These must be running on each system, a Zeroconf daemon.
Finding of BitTorrent caching
The BEP 22 in extension ( currently in draft ) described allows the network- topologically obvious nodes such as buffers from an ISP tracking.
This can be useful in many ways: by ISP traffic from popular torrents on their network cache and dine operated on their network clients from the cache, the more expensive external traffic can be saved. For customers, this results in an improvement in the reliability of the torrent and the download speed. The data of torrent transfers can thus take less complicated routes through the Internet.
This extension has been introduced with version 4.20.0 of the original clients ( mainline ).
Protocol obfuscation
Many clients now offer encryption of the data stream using the algorithm RC4 ( stream cipher ) and the " Infohash " of the respective torrents as the key to disguise the protocol of the data stream, and Internet service providers to complicate the traffic shaping.
The initial developer of the BitTorrent protocol Bram Cohen believes that this is bad, and the corresponding BEP (BEP 8) is reset.
For customers of some ISPs, it is the only way a selective throttling their data to avoid intercourse, on the other hand, it takes the party, the possibility of operation of BitTorrent caching and needs more processing power.
UTorrent and Azureus led the expansion of a composite, which suddenly made a majority of peers compatible with encrypted connections.
Peer Exchange
Peer Exchange ( PEX) is an alternative method for detecting peer. Thus, peers can exchange peer lists with each other and thus additional peers are sourced from affiliated peers. Although the corresponding BEP 11 is not yet adopted, the process is already widespread.
Internet Cache
As of version 4.20.0 BitTorrent supports the Internet Cache Protocol (ICP ), to protect the data transmission rate of the provider. For this purpose, the Additional Protocol Cache Discovery Protocol has been defined. So far, the technique has not yet been used. Since caching provider does not have to be liable for the traffic that passes through through the Digital Millennium Copyright Act ( DMCA), composed at least in the United States legally no problems.
Anti-leech Tracker (ALT)
BitTorrent is based - like all the file-sharing networks - on the principle of " give and take". Quite a few participants deactivate their own transmission function ( "upload" ) and thus disregard the principle of all file-sharing networks. In response to this exploitation to have established so-called " Anti-leech Tracker " ( ALT), observe the behavior of participants steadily and participants who only download or do this in unfair ratio, exclude from the network when you violate predefined rules. As a benchmark here the so-called ratio ("file ratio", "overall ratio" or the uTorrent "Share- rate "), which is calculated by dividing the amount of data sent and received.
In this system, however, participants are disadvantaged with lower data transfer rate. So it can happen that such users will be banned from the ALT if they can not keep their ratio in time. Therefore, the procedure on some ALT with the so-called "Only Upload" against this abuse. In "Only upload " only the mass will be credited to uploaded data. Furthermore, this problem is also reinforced with a so-called " Seedbonus " encountered in the points for the time period of the transmission process ( "upload" ) will be awarded, which in turn can then be exchanged for " upload credit".
Another problem: The ALT relies on calculating the ratio of reports of the participating clients. These can easily be corrupted, either intentionally through manipulation of cheaters or accidentally by improperly configured client software. Here, methods have been developed in the meantime, however, recognize such potential fraud and thus lead to immediate expulsion.
Future developments
In the future, the development of the protocol is no longer supported by Bram Cohen alone, but also by other developers. BitTorrent users are affected lately increasingly ( sometimes unknowingly ) by the traffic-shaping their provider. Are there packages classified as P2P packets, the upload is strongly throttled in many cases. In response, the client Vuze (formerly Azureus ) and uTorrent implemented an end-to -end encryption ( with RC4 stream cipher ) to bypass traffic shaping. BitComet, rTorrent, Transmission and KTorrent support the new protocol encryption also.
History
The BitTorrent protocol was designed by the programmer Bram Cohen for the Bootlegger online community etree in April 2001. On 2 July 2001, he published a first implementation that is now being cared for by his company BitTorrent, Inc.. After a short time started the file sharing scene to take advantage of the technology among others for swapping of unlicensed copies of copyrighted data. Over time, became the largest BitTorrent ( content, users, traffic) file-sharing network, it produces one-third of the total global Internet traffic.
The U.S. company called BitTorrent has end of February 2007 converted their eponymous website in an online store in which can be a lot of media contents only charge download.
Areas of application, advantages and disadvantages
Is particularly well suited BitTorrent for fast distribution of large files for which a currently high demand exists. For slightly older or less popular files may download via FTP or HTTP because of the insufficient number of uploaders is preferable. This disadvantage can be overcome by the use of so-called Webseeds. The process of data distribution with BitTorrent is fundamentally different from the way the well-known file- sharing networks, where everyone can offer their own files in parallel. The increasing deployment of tracker -less techniques and search functions in the clients they can be but also how to use traditional file sharing.
Since the size of the data transfer rate that can get any downloader, on the amount of finished goods and the amount of unfinished downloads (peers ) in the network and the upload rate of user dependent, it may, depending on the amount of the provider ( seeding ), the downloader ( Leecher ) and the distribution rate in more or less kilobytes per second. As a user with virtually full download required no download rate, the maximum available data rate increases for the entire network, because this final user only uploads ( seedet ). Conversely claim Downloader data transfer rate, but themselves contribute to their upload rate. On the following ( very theoretical ) example, the effect of different amounts of pure providers ( seeds ) and downloaders ( leechers ) should be displayed:
- 5 full downloads, each of the terminals has on average an upload rate of 30 kilobytes per second: 5 × 30 = 150 Kbytes / s
- 10 incomplete downloads, each of the terminals has on average an upload rate of 30 kilobytes per second: 10 × 30 = 300 kB / s
The total data rate in the network is thus 150 KByte / s plus 300 Kbytes / s, for a total of 450 KByte / s Since 10 users download simultaneously, these available data transmission rate is divided into 10 × average of 45 KByte / s
In reality, such a value is reached but mostly on large public trackers only popular torrents going because of data transmission rate by waiting times, assignments, different accessibilities, etc. lost. Moreover, in practice, different connection speeds and priorities for a more or less fast downloading are responsible. In addition, many users have their client or their firewall configured incorrectly.
On Anti-leech trackers (see explanation above) are those and still much higher download rates, however, very often encountered. Here you can also fast connections such as DSL 16000 with download speeds beyond 1000 KByte / s optimal use.
For use in the practice
Red Hat and Novell among the first Linux distributors who used BitTorrent to distribute their distributions. Meanwhile, all known Linux distributions and FreeBSD are available via BitTorrent. The game developer Blizzard distributed the World-of- Warcraft - beta via BitTorrent and is now, like id Software, the larger patches for the final version also available as torrents. Also OpenOffice.org and LibreOffice can be downloaded via BitTorrent. Facebook and Twitter to distribute it to their server via Bittorrent.
Even outside the software area, there are concrete applications: The BBC is currently undertaking pilot projects to provide current programs and documentaries immediately after the broadcast online via BitTorrent available. The Open Music Project Jamendo albums distributed via BitTorrent. The podcasts of Chaos radio network are distributed via BitTorrent since 2010.
Others
One study of ipoque in February 2009, according to accounts for the data transmission via the BitTorrent protocol in Germany 37% of all data traffic and therefore occupies the top spot by a wide margin to HTTP with a share of 15%.
Furthermore ipoque indicates that BitTorrent is the only file sharing protocol that will be used significantly for legal content.
In the meantime, Google has the word does not appear bittorrent on the AutoComplete function.
Terms of Use
The legality of operating from torrent sites or servers tracker with torrents, can be spread over the copyrighted material without authorization is controversial because the servers themselves offer no files, but only connect the peers to each other.
In the past it was more common to seizures of servers that offered Torrents. The first large-scale action took place in December 2004, when the Finnish police raided on the server side Finreactor. The torrents are no longer offered since then, and the case was closed. In May 2005, joined the U.S. authorities and the FBI to the Department of Homeland Security Immigration and Customs Enforcement subordinate the page EliteTorrents.org. The so far biggest torrent site, Suprnova.org was seized in December 2005 by the Slovenian authorities. The page LokiTorrent, probably that time the largest torrent search engine behind Suprnova, has also set shortly after the service. Supposedly, the Administrator Edward Webber of the MPAA was legally forced to pay a fine and publication of the log files.
The hitherto most spectacular action took place in May 2006, when the world's largest BitTorrent tracker ThePirateBay.org was confiscated under pressure from the U.S. Department of Justice by the Swedish police, but was a few days later on the power again. In February 2009, four of the operators of The Pirate Bay were indicted by the Swedish courts and sentenced in April each year prison sentences as well as damages in the millions. This is significant in that it was about providing copyright- protected material, but in itself not on the servers of the operator. The judgment is not yet final.
In this context, it is now also often used by P2P " privacy " or P2P Privacy speech. Basically, it is possible for anyone to make a BitTorrent tracker server to the network, including copyright protection organizations and criminal investigative authorities. In addition, of course, the aforementioned organizations and institutions to participate and, if appropriate, obtain thus a " proof " of the transmitted in the P2P network, respectively exchanged files on the actual peering ( data exchange). Since it is difficult to understand for the user on the BitTorrent client side, which tracker server or peer ( IPs) were, only " attempt to eavesdrop ," there are efforts and projects, to want to achieve better protection of privacy on P2P networks. One approach to this is to simply block certain IP numbers via IP lists and thus excluded from the respective torrent. One example is called Peer Guardian.
According to a study by the UK University of Birmingham 's own IP address is logged with copyright offenses in the BitTorrent network within three hours from investigators. However, the IP address by anonymizing services such as proxy servers and virtual private networks (VPNs ) are hidden.
For more information on the legal situation are located under file sharing.