Torrents 101: How Torrent Downloading Works

Part 1) An Overview of Bittorrent P2P File Sharing

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Question: What exactly is "bittorrent" sharing?

Answer: Bittorrent networking is the most popular form of modern P2P (peer-to-peer) file sharing. Since 2006, bittorrent sharing has been the primary means for users to trade software, music, movies, and digital books online. Torrents are very unpopular with the MPAA, the RIAA, and other copyright authorities, but are much beloved by millions of college and university students around the planet.



Bittorrents (also known as "torrents") work by downloading small bits of files from many different web sources at the same time. Torrent downloading is extremely easy to use, and outside of a few torrent search providers, torrents themselves are free of user fees.

Torrent networking debuted in 2001. A Python-language programmer, Bram Cohen, created the technology with the intent to share it with everyone. And indeed, its popularity has taken off since 2005. The torrent community has now grown to millions of users worldwide in 2009. Because torrents strive to screen out dummy and corrupt files, are mostly free of adware/spyware, and achieve amazing download speeds, torrent popularity is still growing fast. By straight gigabytes of bandwidth used, bittorrent networking is the most popular activity on the Internet today.

How are torrents special? How is the torrent community different from Kazaa and other networks?

Answer: Like the other file-sharing networks (Kazaa, Limewire (now defunct), Gnutella, eDonkey, and Shareaza) Bittorrent's primary purpose is to distribute large media files to private users.

Unlike most P2P networks, however, torrents stand out for 5 major reasons:
 

  1. Torrent networking is NOT a publish-subscribe model like Kazaa; instead, torrents are true Peer-to-Peer networking where the users themselves do the actual file serving.
  2. Torrents enforce 99% quality control by filtering out corrupted and dummy files, ensuring that downloads contain only what they claim to contain. There is still some abuse of the system, but if you use a community torrent searcher like www.isohunt.com, users will warn you when a torrent is a fake or dummy file.
  1. Torrents actively encourage users to share ("seed") their complete files, while simultaneously penalizing users who "leech".
  2. Torrents can achieve download speeds over 1.5 megabits per second.
  3. Torrent code is open-source, advertising-free, and adware/spyware-free. This means that no single person profits from torrent success.
     

Related: How to speed up your torrent download speeds with port forwarding...

Next: A non-technical explanation of bittorrents

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Question: How exactly does bittorrent sharing work?

Answer: Torrent sharing is about "swarming and tracking", where users download many small bits from many different sources at once. Because this format compensates for bottleneck points, it is actually faster than downloading a large file from a single source.
 
  • "Swarming" is about splitting large files into hundreds of smaller "bits", and then sharing those bits across a "swarm" of dozens of linked users.
  • "Tracking" is when specific servers help swarm users find each other.
  • Swarm members use special Torrent client software to upload, download, and reconstruct the many file bits into complete usable files.
  • Special .torrent text files act as pointers during this whole process, helping users find other users to swarm with, and enforcing quality control on all shared files.


Comment: Torrent vs. Kazaa. Torrents are different from the competing Kazaa network in one significant way: torrents are true P2P sharing. Instead of "publisher servers" dishing out files, torrent users do the file serving. Torrent users voluntarily upload their file bits to their swarm without payment or advertising revenue. You could say torrent users are motivated, not by money, but by a "Pay-It-Forward" cooperative spirit. If you recall the Napster.com model of the 1990's, bittorrent swarming is the same, but with sharing incentive added.

Torrent sharing goes like this: if you share files via bittorrents, you will be rewarded with increased download speed. Conversely, if you choose to "leech" and not share your files upwards, you will be punished with slow Torrent download speeds.

Download speed is controlled by torrent tracking servers, who monitor all swarm users. If you share, tracker servers will reward you by increasing your alotted swarm bandwidth (sometimes up to 1500 kilobits per second). Similarly, if you leech and limit your upload sharing, tracking servers will choke your download speeds, sometimes to as slow as 1 kilobit per second. Indeed, the "Pay It Forward" philosophy is digitally enforced! Leeches are not welcome in a bittorrent swarm.

Next, Part 3: "OK. I want to try torrent downloading. How do I start?" (continued from previous page)

Question: How do I start using bittorrent?

Answer: Bittorrent "swarming" requires six major ingredients.
 
  1. Bittorrent client software (there are dozens of choices, all free to install. See next page for software suggestions.).
  2. A tracker server (hundreds of them exist on the Web, no cost to use).
  3. A .torrent text file that points to the movie/song/file you want to download.
  1. A Torrent search engine that helps you find these .torrent text files. (See next page for torrent search links.)
  2. A specially-configured Internet connection with port 6881 opened on the server/router to allow torrent file trading.
  3. A working understanding of file management on your PC/Macintosh. You will need to navigate hundreds of folders and filenames to make file sharing work for you.


Next, Part 4: the step-by-step download process.

Setup Comment: At the very worst, it will take you about one day to set up your PC or Mac for torrent swarming. If you don't employ a hardware router or software firewall with your modem, then setup will likely take only 30 minutes of choosing and installing your bittorrent client. If you do use a hardware router or firewall (which is a smart way to configure your home machine), you are likely to get "NAT" error messages at first. This is because your router/firewall has not been taught to "trust" your bittorrent data yet. Once you open digital port 6881 on the router/firewall, the NAT messages should stop and your bittorrent connection should work just fine. Check this page for help on setting your Internet router.

See Page 4 of this article for bittorrent client software suggestions.

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Question: What exactly are the Bittorrent download steps?

Answer, Part 1: Copyright warning. Unless you live in Canada, you must understand that copyright laws are commonly violated by P2P sharing. If you download/upload a song, movie, or TV show, you do risk a civil lawsuit. Canadians are somewhat protected from these lawsuits because of a Canadian court ruling, but not residents of the USA or most parts of Europe and Asia.

This lawsuit risk is a reality, and you must accept this risk if you choose to download P2P files. Click here for more details on this copyright controversy.

Answer, Part 2: The torrent download process goes likes this:
 

  1. You use special torrent search engines to find .torrent text files around the Net. A .torrent text file functions as a special pointer to locate a specific file and the swarm of people currently sharing that file. These .torrent files vary from 15kb to 150kb file size, and are published by serious Torrent sharers around the world.
  2. You download the desired .torrent file to your drive (this takes about 5 seconds per .torrent file at cable modem speeds).
  3. You open the .torrent file into your torrent software. Usually, this is as simple as a a double-click on the .torrent file icon, and the client software auto-launches. In other cases, this software will even open the torrent file for you.
  1. The torrent client software will now talk to a tracker server for 2 to 10 minutes, while it scours the Internet for people to swarm with. Specifically, the client and tracker server will search for other users who have the same exact .torrent file as you.
  2. As the tracker locates torrent users to swarm with, each user will be automatically labeled as either a “leech/peer” or as a “seed” (users who have only part of the target file, versus users who have the complete target file). As you might guess, the more seeds you connect to, the faster your download will be. Commonly, 10 peers/leeches and 3 seeders is a good swarm for downloading a single song/movie.
  1. The client software then begins the transfer. As the name “sharing” implies, every transfer will happen in both directions, “down” and “up” (leech and share).
    *SPEED EXPECTATION: Cable and DSL modem users can expect an average of 25 megabytes per hour, sometimes slower if the swarm is small with less than 2 seeders. On a good day with a big swarm, however, you can download a 5MB song within 3 minutes, and a 900MB movie within 60 minutes.
  2. Once the transfer is complete, leave your torrent client software running for at least two hours. This is called "seeding" or "good karma", where you share your complete files to other users.
    Suggestion: do your downloads just before you go to sleep at night. This way, you will seed your complete files, you will increase your upload/download ratio, and you will have complete downloaded files by the time you wake up!
  3. Movie and music plug-ins: you will likely need to install media players and updated codec converters to play your downloads:
  1. Enjoy your movies and songs!
  2. Fair warning: you will want a second hard drive once you start serious torrent downloading. Songs and movies require large disk space, and an average P2P user commonly has 20 to 40 GB of media files at any one time. A second 500GB hard drive is common for serious P2P users, and the recent low prices on hard drives make it a good investment.
     

Other resources you will need for Bittorrent downloading:
 

  1. Here is a list of good torrent search engines.
  2. Here is a list of good torrent software for PC and Mac.
  3. Here is the original torrent client software (no GUI, just console).
  4. Bittorrent Frequently Asked Questions.
  5. Meet Bram Cohen, the torrent creator.

 


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