Author Topic: What's up with Bit Torrents? (Read 1741 times)

Balog · « **on:** June 19, 2007, 01:03:05 PM »

Ok, so I keep hearing about torrents of one kind or another, but I gotta admit I'm not %100 clear on the subject. The Wiki entry was mostly technical and didn't really address my questions, so as always I turn to my forum dwelling tech support. grin

My understanding is that it's basically just another form of peer to peer file sharing tech ala original Napster, Kazaa etc etc. I know from experience how full of mal ware those older progs were, and yet I see technically savvy people using it. Has the new tech done away with the bad, or are they just blocking it somehow?

Secondly, I know there are a ton of variations on the torrent theme out there; which one(s) would you recommend?

Cromlech · « **Reply #1 on:** June 19, 2007, 02:07:36 PM »

Yeah, it's just peer to peer stuff. Usually, the places that link to torrents will remove one that users report as a bad one. For torrents, I personally prefer to use Azureus or uTorrent.

http://azureus.sourceforge.net/

http://www.utorrent.com/

Harold Tuttle · « **Reply #2 on:** June 19, 2007, 03:08:20 PM »

Its a many to one peer setup...

The file is sliced up,
and if 30 people have the file
you get slices from each of their upload bandwiths.

As you start acquiring pieces of the file, you start seeding slices out to any other requesters.
The more seeders, the faster you get the whole file.
Once you get the file, you are supposed to keep it open for awhile to assist in the dispersal.

it is rumored that this may be used in the near future to distribute legitimate digital movie files.

Firethorn · « **Reply #3 on:** June 19, 2007, 03:33:39 PM »

It's something like napster, but more distributed and without a browsing client.

You download a 'torrent' file that contains the tracker's IP address, file information and CRCs and such.

Note: The tracker does NOT serve the actual data, it's only a informational source. If it does serve data, that's because it's been configured to act that way.

You load this into a client, that connects to the tracker, which passes out information about other peers(leechers) and seeds. Your client connects to them to download the file. Once a portion is downloaded, the client will start sharing out the parts it has to others. Once the download is complete, you become a seed.

It's a robust system because the tracker is also an open piece of software, there's no central point to shut down the networks. Many clients today can also act as a tracker. There's also been modifications to allow peers/seeds to act as limited trackers, so even the loss of the tracker isn't fatal.

So you can end up with situations where a website hosts a torrent file for download,
A completely different server acts as the tracker
Anywhere from 0* to hundreds of thousands of peers and seeds. (With a limited ability keep the network up even without the tracker)

*With no seeds the odds of getting the complete file drops drastically. Doesn't mean that somebody won't 'reseed' IE come up with the complete file. Meanwhile the peers will all share what they have. Once a seed(or a peer with the missing parts) comes up, the parts will be shared to several peers, who then start distributing those parts to others.

Balog · « **Reply #4 on:** June 19, 2007, 05:00:50 PM »

Ok, I think I get the idea behind it. I'm still not clear about one thing, though. Are torrents a generic file type like .avi or .mp3; or are they specific to a certain program ie utorrent users can only Dl utorrent torrents?

Anyone else have any experience with the versions Cromlech posted? Any built in malware or security issues known with them? Any other recommendations? I know Tyme and GunnySkox have mentioned getting torrents in the past; anyone know what they use?

Harold Tuttle · « **Reply #5 on:** June 19, 2007, 06:38:35 PM »

i run Azureus
http://azureus.sourceforge.net/

any file type can be turned into a .torrent

once you have all the parts, the torrent recreates the original file type

Balog · « **Reply #6 on:** June 19, 2007, 08:13:30 PM »

Hmmm, Azureus is seconded... do I hear the requisite third to get it installed here at la casa de Balog? grin

Vodka7 · « **Reply #7 on:** June 19, 2007, 08:41:34 PM »

Another vote for uTorrent.

To answer your questions--the .torrent file is something like an .html file. You open it in a program and Magic Happens. Like any browser, any BT client can open any .torrent file. Like others said, the .torrent file itself is basically a link to the tracker which connects you to other people downloading/seeding the file, and you actually download through them. What you'll be downloading will be mp3s or rars or avis or other fun stuff.

www.btjunkie.org is the biggest BT index. If you're looking for something, it will be there, or it won't exist.

Firethorn · « **Reply #8 on:** June 20, 2007, 02:36:01 AM »

I use Azureus as well. Tried a different one back in the day, switched to Azureus so I don't have dozens of little windows cluttering things up.

Torrents are a generic file; as long as it's built to spec any client will be able to load it.

tyme · « **Reply #9 on:** June 20, 2007, 05:26:15 AM »

Azureus is pure bloat. It may be the slowest popular app I've ever seen. Java doesn't have to be that slow, but I'm sure being java doesn't help.

uTorrent... uTorrent + wine if you're using linux.

As for sites, I like isohunt because the people who run it seem to know what they're doing technically, but btjunkie is fine too.

Sergeant Bob · « **Reply #10 on:** June 20, 2007, 09:35:16 AM »

I use uTorrent and like it. Haven't tried Azureus though.

InfidelSerf · « **Reply #11 on:** June 20, 2007, 12:08:00 PM »

I'll put a 3rd in for utorrent
There are several browser based clients in the works as well.
http://torrentfreak.com/6-ways-to-download-torrents-with-your-web-browser/

Nick1911 · « **Reply #12 on:** June 20, 2007, 12:20:35 PM »

Am I the only person in the world that used the original Bittorent?

Sergeant Bob · « **Reply #13 on:** June 20, 2007, 12:45:27 PM »

Quote from: Nick1911 on June 20, 2007, 11:20:35 AM

Am I the only person in the world that used the original Bittorent?

Well, the world can be a lonely, lonely place.... sad

Balog · « **Reply #14 on:** August 07, 2007, 06:24:18 PM »

Ok, so I've got Utorrent, and I'm trying to download from btjunkie. Question; what do all the parameters mean, and how do they affect the dl'ing? I'm referring to "seed, leech, and health" which seem to be the big three as far as sorting go.

client32 · « **Reply #15 on:** August 08, 2007, 02:33:51 AM »

Seed is the number of people who have the full file and are sharing (seeding) the file.
Leech is the number of people who are currently downloading, they could have 0% to 99% of the file. When you start downloading, you will add to the leech number.
Health, I don't know about.

Forgot to add:
The more people in the peer list (seeders and leechers), then the better chances you have of a fast download.
If there are 0 seeds then you are not going to get all of the file. I suppose in theory that all of the file could be in the swarm, but I have never seen it work that way.

tyme · « **Reply #16 on:** August 08, 2007, 03:54:18 AM »

To further avoid the "magic happens" explanation...

Bittorrent websites list a bunch of links to .torrent files. They tend to have searchable databases, but the core functionality is that they somehow collect .torrent files (by upload or by grabbing them from other sites), and then provide those .torrent files for you to download.

.torrent files store information about a collection of files. A single .torrent file can describe a single file (say an mp3 or jpeg), or it can describe a directory tree with thousands of files of various kinds. .torrent files themselves are fairly small, generally 1kb to 512kb, depending mainly on how many blocks* the torrent contains.

There's a lot of advanced functionality in .torrent files, but the basic information they contain are:
a) a list of trackers that (possibly) are tracking the torrent
b) a hash for each block* of the collection of files specified by the torrent

Bittorrent trackers speak http but not the kind your browser speaks. A bittorrent client (azureus, utorrent, etc) connects to one of the trackers listed in a .torrent file, asks for a list of peers that are leeching or seeding that particular torrent, and uses that list to figure out who to connect to in order to get more blocks* from the torrent.

When you load a .torrent file into a torrent client, it connects to the tracker(s) listed in the file, tells the tracker(s) that it is a peer for that torrent, and gets a list of other peers for that torrent.

Suppose you have a collection of pictures you want to provide as a single torrent. uTorrent or Azureus or various other programs will let you specify the directory the images are in, and will create a .torrent file describing that directory. Roughly, it takes all the files, glues them together, and divides them up into blocks*. These blocks can be smaller like 64kb or larger like 16MB. For each block, it computes a value (hash) that it can use to check for corruption when it receives a block of the torrent from another computer. It also asks for and stores the primary tracker url for the torrent. It adds various other stuff to the torrent, but those are the main things.

Then you have to upload that newly-created .torrent file to the primary tracker you specified. This generally requires you to have an account on the tracker site.

After that, you can load the .torrent file in your bittorrent client (if it isn't already loaded), and other people can download your .torrent from the tracker site. Their torrent clients see the primary tracker url in the file, connect to that tracker, find out that your computer is also linked to the torrent, and then they start requesting blocks of the torrent from your bittorrent client.

I think I got that right, but I haven't actually read the bittorrent spec... Sad

tyme · « **Reply #17 on:** August 12, 2007, 07:01:15 AM »

I just discovered a new bittorrent client that's lean (not quite as lean as utorrent, but not even close to the bloated Azureus): Transmission.

Quote

If there are 0 seeds then you are not going to get all of the file. I suppose in theory that all of the file could be in the swarm, but I have never seen it work that way.

This really does happen sometimes, although it is rare. A seeder will send a complete set of blocks distributed among multiple other clients, then drop out of the cloud. Or a seeder will go missing after seeding maybe 80% of the torrent, and someone who happens to have the incomplete files, but not the entire torrent, will join up to get the torrent to 100%.

Tends to happen more on private trackers where people care about the community, rather than on public sites where nobody care if 100 desperate leechers are at 95%.

Vodka7 · « **Reply #18 on:** August 14, 2007, 11:43:55 AM »

Quote from: tyme on August 12, 2007, 06:01:15 AM

I just discovered a new bittorrent client that's lean (not quite as lean as utorrent, but not even close to the bloated Azureus): Transmission.

Just a note--Transmission is still banned on some trackers because older versions used to do Bad Things. The developers fixed this, and most trackers allow the new versions, but it's something to be aware of, especially on smaller trackers that may not know of the goodness of the new versions. Personally, I still prefer the curses version of the official BT client on mac and linux.

To answer another question--the Health number/graphic on some trackers/indices is really just another way of showing the ratio of seeds to leechers. It's pretty much useless.

Oh, and another tip for BT that just occured to me. Limit your upload rate to about 75-80% of your max capacity. (That is, if you can upload 40k/s, keep it capped to around 30k/s.) Most american high speed services are not synchronous, and uploading at your max speed like BT loves to do will make other downloads and even web browsing slow to a crawl.

News:

Author Topic: What's up with Bit Torrents? (Read 1741 times)