What is Bittorrent?

Introduction

Bittorrent is a decentralized peer to peer (P2P) distribution of content which uses the upload bandwidth of each individual who is downloading the content, and those who have downloaded, to transfer the content.

The bittorrent transfer is initiated through either a .torrent file or a magnet link.  Either of these is associated with specific content and when opened in a bittorrent client, transfer of that associated content begins.

From its inauspicious start in 2001, bittorrent has grown to one of the major forces on the internet.  Estimates of bandwidth use by bittorrent are one third, and upwards, of all internet use.
There are presently over 17 million torrents active and many petabytes of content associated with those torrents.

Unfortunately, the use of bittorrent to illegally distribute copyrighted content has overshadowed bittorrent's advantages in the distribution of legal content.

This article is part of a series of articles on bittorrent here at Gizmo's Freeware.  If you are not familiar with bittorrent, then before using this article you should read these:

Comparison of Distribution Methods

Central Server - Traditional downloads from the internet use a central server to provide the bandwidth for the transfer.  All who want the download, obtain their copy from the same source. 

Traditional P2P - The first incarnations of peer to peer transfers (Napster etc.) worked similarly to central server.  An individual served as a server distributing content to others using the upload bandwidth of that individual's internet connection.  While the distribution method was similar, P2P was "off the main grid" and involved distribution between individuals, hence the peer to peer (P2P) designation.

Bittorrent - was the next step in the evolution of transfers and P2P.  It differs from traditional central server and traditional P2P distribution, in that it involves the use of multiple sources for the distribution of the content.  Each active user is involved in the distribution of the content through their upload bandwidth.  It also provides a fail safe against the corruption of distributed content.

normal-distribution-imageThese diagrams roughly show these distribution methods.  Since central server and traditional P2P essentially distribute the same way, the "normal" network distribution image reflects both of these methods.
Advantages of Bittorrent over Traditional Distribution Methods

Virtuous circle vs Viscous Circle

  • Bittorrent - the more users active on a torrent provides for greater speed for each of the users. 
  • Central Server & Traditional P2P - The more users active on a download results in decreased speed for each of the users.

In bittorrent the upload bandwidth of every active user on a torrent is used to transfer the content.  This means that the more popular the content, the greater the download speed for each user.

A central server, or individual serving as a central server in traditional P2P, has a limited amount of bandwidth for distribution.  The more users seeking the content, the less the download speed of each user. 

Integrity of Content

  • Bittorrent - The torrent file or the magnet link that is used to initiate the distribution contains unique and specific information on the content that will be downloaded through either.  The content is broken down to bits to facilitate distribution among the active users.  If any of these bits becomes corrupt during transfer, and therefore does not match the information within the torrent or magnet link, then it will be rejected by the bittorrent client and replaced with an uncorrupted bit.  This ensures that when the download is complete it will be an exact copy of the distributed content.
  • Central Server - Distribution through a central server always involves some risk of corruption and this issue is worsened when the demand for the content is high.  There is no fail safe guard against such corruption of content.
  • Traditional P2P - Suffers from the same issues as a central server.  Since traditional P2P is "off the grid", the risk of distribution of malware is increased, making this the most dangerous of distribution methods.
Definitions Of Common Bittorrent Terms

Definitions of common bittorrent terms in simple (hopefully) language.

Torrent - A small text file that contains information about specific (associated) content, file and folder names within the content and about tracker(s).  These are used to begin download of the associated content when opened in a bittorrent client.

Magnet Links are similar to torrents in that they are used to download associated content when opened in a bittorrent client.  They differ in that they are not files, only links.  The magnet link only contains information on the content and no tracker or file and folder information. 
This is an advantage for bittorrent search sites as they do not need to store files, only bits of data relating to the magnet link.  Additionally, this further decentralizes bittorrent as a tracker is no longer needed.
This is an advantage for users as the magnet link looks for the content only and if the file or folder names are different the magnet link may still download.  A torrent file will only download when the content and file and folder names are identical.  This could help increase download speed, particularly if the content is rare.

Torrent Search Site - A site that indexes torrent files and their associated content.

Tracker - A communications hub that helps people active on a torrent connect to each other.

Bittorrent Client - A program that opens torrent files to transfer of the content associated with the torrent.

Seeds - Those who have 100% of the torrent's associated content and are uploading to Peers (Leechers).

Peers - Two definitions.

  1. Those active on a torrent who have less than 100% of the content associated with the torrent.  They download from seeds and other peers and upload to other peers. (Most bittorrent clients use the term this way).

  2. All of those active on a torrent, i.e., those who have 100% and those who have less than 100%. (Most torrent search sites use this definition).

Leechers - Two definitions

  1. Those who have less than 100% of the content.  They download from seeds and other leechers and upload to other leechers. (Some torrent search sites use this term).

  2. Those who download 100% of a torrent's associated content, but do not upload back at least 100% of that content. (Used by all. This negative connotation is why bittorrent clients use peers for the above definition.)

Ratio - The amount uploaded divided by the amount downloaded.  Usually shown per torrent and overall within the bittorent client.. 

Swarm - The group of people active on a single torrent. (Same as definition 2 of Peers, above)

DHT - Short for Distributed Hash Table.  A way of connecting to other users without the tracker being involved.  Especially useful when a tracker goes down or for hosting tracker-less torrents.

PEX - Short for Peer Exchange. A way of connecting to other users without the tracker, through people that you are already connected to.  Especially useful if tracker is down.

Encryption - Primarily designed to help users avoid interference from an Internet Service Provider (ISP).

How it Works

This is a non-technical description of the bittorrent process.

A user goes to a torrent search search site to search for content.  When the user finds wanted content, the user downloads the .torrent file (or magnet link) associated with the content.  When the torrent (or magnet link) is opened in a bittorrent client, transfer of the associated content begins.

When the download is begun with a torrent, the bittorrent client communicates to a tracker through the information contained in the .torrent file.  A tracker essentially serves as a communications hub for this swarm of individuals, helping them find each other.  DHT and PEX also help users to find each other. 
With a magnet link, the bittorrent client uses DHT and PEX to find other users with identical content.

Bittorrent works by splitting content files into hundreds of smaller “bits” and sharing those bits, using the upload bandwidth of the active users, across a swarm of linked users.  These bits are downloaded randomly, so the content is generally not useable until the download is complete.  The bittorrent client will reject any bits that do not match the information contained in the torrent file.  This ensures that the completed download will be an uncorrupted copy of the content.

Conclusion

As a process for the transfer of content, bittorrent is clearly superior to traditional methods.  Any organization would be wise to use the bittorrent protocol for the transfer of communications between separate offices.  This would result in less cost in distribution and assurance of accuracy in the transferred content.

Hopefully this article has given you a basic understanding of the bittorrent process.  If you have any questions, or comments, feel free to post below and I will try to address them.

This article is part of a series of articles on bittorrent here at Gizmo's Freeware.  After reading this article, if you are interested in bittorrent, then you may check out these other articles here at Gizmo's

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Comments

by Ambrose Ohis (not verified) on 4. November 2012 - 20:36  (101889)

i've got nothing but thanks for this and other wonderful articles on this site. this is my first visit and i've bookmarked.....

by Zaheer Khan (not verified) on 22. August 2012 - 20:28  (98163)

I love Gizmo's Website. I use to say this website is my "PEER", this word is used for "Great Spiritual Guide" in our country. I always follow this website's instructions to select different software for my daily uses. I feel this website as my teacher.
*...................................................
My question is about "Magnet link" and "Torrent" which should we prefer to download. as i think that magnet link is better than torrent.
My second question is that i delete torrent files after loading them in client (before complete downloading) can it decrease the speed.

by mr6n8 on 22. August 2012 - 21:11  (98166)

Theoretically, a magnet link could potentially be faster as the magnet can download from clients active on a separate torrent with identical content. There is no downside to magnets as opposed to torrents.

In my experience, I have found there to be no difference. In my recent testing for the Best Free Bittorrent Client review here, I used a torrent and magnet link for the identical content. There was no difference in speed.

Since magnets take a little longer to get going, torrents might be preferable for smaller content (under 100MB), but only slightly. Otherwise, magnets would be preferable, but again the difference is negligible.

Deleting the torrent file will not hurt speed once the torrent is going, but it is a good practice to keep the torrent files in case there is an issue where the torrent has to be re-added to the bittorrent client. Most bittorrent clients create a separate torrent file in the folder designated within the client. So, even if you delete the torrent you started with, there is another torrent file available. The same goes for magnet links - in most clients a torrent file is created.

Interesting on the word "peer" in your culture. As a former practicing lawyer in the USA, the word "peer" has always meant "equal" to me (as in a jury of one's peers). Although I like "great spiritual guide" better. I wonder where the differential sprung from.

Steve

by Zaheer Khan (not verified) on 23. August 2012 - 0:26  (98173)

Now i'm cleared. thank you.
*-----------------------------
I have printed all your articles about torrents.
they are very helpful...
i'm still reading them.
*-----------------------------
i was using Bittorent Client but after reading your article "Best Free BitTorrent Client" now i have just downloaded qbittorrent. After checking it i will share my experience with you.
*-----------------------------
I like Extratorrent search site it has advance search option which i like most it can search by categories, subcategories it has a nice user interface with catagories icons, reigon icons...
please give us some remarks on this site...
*-----------------------------
In the end i'm so thankful of you Sir Steve because i know a lot of things about torrents due to you.

by mr6n8 on 23. August 2012 - 0:41  (98175)

Thank you. I am always glad to hear that I helped.

I took a look at ExtraTorrent and it looks good. I am going to take a further look, but I may well add it to my best free torrent sites listing. From what I saw there was a good amount of torrents from "trusted uploaders", which is always good. Also a good selection. Thanks for that.

I will be looking forward to your comments on qBittorrent. BitTorrent is also an excellent client.

Steve

by Emma (not verified) on 27. January 2012 - 9:56  (87877)

HI, can you tell me if Demonoid is safe? I joined it a while back and want to start downloading things. If I follow the instructions above, it should work, right? But how do I upload things back so that I get a good ratio? Thanks!

by mr6n8 on 27. January 2012 - 19:10  (87905)

Not exactly sure what you mean by safe.

I have never seen a torrent at Demonoid that contained fake material, so in that sense it is very safe.

Demonoid is not a true private site. It is commonly referred to as a semi-private site. DHT and PEX are allowed on torrents, so non-members can connect. Also, many of the torrents are available to non-members.
So, Demonoid is not as safe as a true private site in that sense.

As far as uploading things back, all you have to do is keep the torrent active after you have completed downloading. Demonoid is a ratio free site, which means they do not ban members who have bad ratios. Still, it is always good to seed back to at least a 1:1 or 100% ratio. Your bittorrent client should have info on the ratio for each torrent.

by QuietCorner (not verified) on 27. June 2011 - 15:58  (74407)

I know nothing about bittorrent beyond this article. I realize the dangers in downloading a file from anywhere, but I'm concerned about the safety of my PC when others are accessing it to download a file. Can a virus be planted that way? And can they get at other files on my PC?

by mr6n8 on 27. June 2011 - 17:24  (74411)

"Can a virus be planted that way?"
I Have been actively following the bittorrent protocol for years and have never heard of a successful attack that way. In fact it is exceedingly rare that the content downloaded from torrents contains malware. Almost all malware attacks in bittorrent come from getting the person to go to a site and download additional content such as a media player, codecs etc.

There are plenty of people who try to spread malware through torrents and if it were possible to attack through the protocol it would have been done and I would have heard of it.

Any fakes or malware can easily be avoided by only downloading content where the comments and/or ratings indicate the content is clean and real. Most torrent search sites (including the ones listed in the Searching for Torrents article here) have ratings and comments to help with this.

"And can they get at other files on my PC?"

No. Only the specific content associated with the torrent is transferred. the other parties have no access to your computer at all. All they get is random bits of the content sent to them through your bittorrent client. All other transfers are communications between the bittorrent clients and the tracker(s).

This would be even less possible than the above, which is pretty much impossible. Again, there has never been any successful attempt at this.

In all the times I have used torrents, only once did I get a fishy download-back when I first started (and did not know about ratings/comments). Even then, because my bittorrent client pre-allocated the content, I was able to see it was not what it was supposed to be and I deleted the torrent before content was downloaded. I reported the torrent and it was removed from the site's listings in minutes.

Steve

Steve

by mr (not verified) on 15. November 2012 - 3:44  (102345)

Thanks Steve for your valuable presentations on different topics.

Here I'd like to comment on your remarks:
"And can they get at other files on my PC?"

No. Only the specific content associated with the torrent is transferred. the other parties have no access to your computer at all. All they get is random bits of the content sent to them through your bittorrent client. All other transfers are communications between the bittorrent clients and the tracker(s)."

I'm not sure about what you are saying because when using bittorrent you are actually uploading some files to others as well. Recently I downloaded a torrent and after opening the .nfo file I was greatly surprised to find in it bits and pieces of content, including email addresses, from my emails in ThunderbirdPortable client! I don't remember whether the Thunderbird was running at the time I was downloading the torrent or not. Here is a part of that .nfo file showing what was copied into it (I've changed the actual email addresses here, but you get an idea what was copied):

<(102=m... )(103
=m... )(104
=Fwd: Welcome to ClickIndia Neighborhood Classifieds!)(105
=CAArV_k_SQBx-Kbr_T+fggqSZyX5hh6tNe5Xyh5q15-Yq25=ECA@mail.gmail.com)
(106=<201203280557.q2S5vmh1009490@my1.clickindia.com>)(108=4f72c07d)
(109=2182)(10A=9a)(1E1=1772|mr)(10D=1b9)(10E
=\$label1 \$label4)(112=107844)>
{1A544:^80 {(k^98:c)(s=9)9:m } [1A544(^88=0)(^8A=0)(^8B=5b)(^82^102)(^85^103)
(^81^104)(^83^105)(^AE^88)(^84^106)(^86^107)(^AF^108)(^89=1)(^87^109)
(^8C=9a)(^9B^8E)(^8F^110)(^B0=0)(^B3^1E1)(^B1=1b9)(^B7^10E)(^B2=0)
(^B4^112)(^9D^110)]}

and there are many more such pieces with emails and even parts of the email content.

Once the download was finished all the torrent files were seeded to others of course.

So this is perhaps the firs incident on stealing private information via torrents that you've heard about?

mr

by mr6n8 on 15. November 2012 - 11:09  (102356)

This most certainly would be the first incident of something other than the content downloaded being involved, if that was what happened.

I am not so sure that was what happened.

Was the torrent download complete when you opened the NFO?

If not, then this would be an issue with the program opening the NFO. I have often seen videos and other content opened before it is done showing other content and I have a feeling that is what happened here.

Did you check the NFO after the content from the torrent completed?

What you are uploading on an active torrent is the bits that you have downloaded through that torrent.

Steve

by mr (not verified) on 15. November 2012 - 14:58  (102371)

I think this was the torrent with the mesmerize.nfo file in it:

I don't want to experiment and start it again though...

Edit: I removed link - Steve

by mr6n8 on 15. November 2012 - 15:53  (102375)

Thanks for that.

I downloaded the NFO and had no issue.

I also Googled the info hash and found the torrent at Vertor (all torrents are verified there to be clean and real). Although I found no real comments anywhere.

I do not know what happened to you in that situation, but I do not think info of yours was uploaded to anyone. But, if I were in your situation, I would also avoid that torrent.

Steve

by mr (not verified) on 15. November 2012 - 16:11  (102376)

Thanks Steve.

by mr (not verified) on 15. November 2012 - 12:27  (102364)

If I remember right the download of the main files was not complete, but the NFO file was complete. But when I saw the content of the NFO file then I stopped the torrent and trashed it.

by mr6n8 on 15. November 2012 - 12:45  (102365)

Very strange indeed.

Do you have a link to the page of the torrent?

There were many attempts to get other content on a user's computer when torrents first started and all of them failed. That approach was abandoned for getting someone to download additional software (special codecs, media players etc). I would be most curious to see this torrent. You can message me the link, or if you post it here, I will delete it immediately after I check it.

Steve

by mr (not verified) on 15. November 2012 - 14:30  (102370)

I've been trying to find it again this afternoon, but without success.
I have painfully slow internet access via mobile so it will take some time, but I'll try again tomorrow.

by wdhpr on 23. April 2011 - 20:05  (70794)

Nicely done!

Clear and easy to understand article.

by mr6n8 on 25. April 2011 - 12:44  (70867)

Thanks for that.

I just redid the article in the hope that it would be clearer.
Hard to tell when I already know.

Steve

by Anonymous on 3. June 2009 - 18:47  (22989)

Oh, good...Thanks...^___^

by Anonymous on 11. December 2008 - 18:33  (11772)

Thank you very much for this useful article and the comments. I love this site as it contains good materials.

by mr6n8 on 24. January 2009 - 19:15  (14617)

Thanks.
Steve

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