How does Bittorent work?

[Kumagoro]

I don't understand how Bittorent works at all. I installed it on my computer and tried downloading some fansubs (I've only watched shows on streaming sites like Youtube before this), but it says it'll take twenty hours for the thing to fully download! It is a big file, but I have a pretty fast computer and it would normally take less than ten minutes for something of its size to fully download. Can I have a geek's help, please?

[Yahshua]

Hm ok I will explain how the Bittorent works for ya. Let say you want a particularly Book title like Lord of the Ring the Bittorent file call .Torrent tell the Bittorrent software how many chapters are in the Book itself. And how many people with an complete copy of the books those are call The Seeders. And rest of them with part of the book is call peers. And as you download the book the speed of your download is rely upon the number of Seeders and their Upload speeds. So if they have good upload speed you get your book faster that way. And in your case an single episode of fansub anime.

[Kumagoro]

I think I've got it... But does it normally take hours for things to download?

[Kaligraphic]

It really depends on how many people are downloading, what parts they have, how many seeds there are, everyone's internet connection speeds, and a host of other factors.

In any case, when you first start downloading in bittorrent, you won't have connections with a lot of peers, so it'll give you a pretty high estimate. Just let it run, and that time should come down.

And, as the lawyers say, don't use this advice to download copyrighted works or to do anything illegal. (standard disclaimer here)

[Nate]

Bittorrent is like...well, to be honest, it's exactly how Penny Arcade described it. Instead of having a file on a server for anyone to download freely, they break it up into a million parts and give each part to a different person. Then magical gremlins invade your PC and put the parts together so you can use it.

Bittorrent is partially good, partially bad. Good because a single person doesn't have to bear the entire load of everyone who wants to download the file. Bad because it's painfully slow and if no one is seeding, you can't download. Ask Radical Dreamer from this site. It took her nearly six days to download something via Bittorrent. Had she been able to download it regularly, it probably would've only taken a few hours.

"Yeah, we figured using Bittorrent was the cheapest way to give you the updates for your game."

"How is it cheaper? I'm still paying like 16 bucks a month!"

"Oh, I'm sorry. I meant cheaper for US. Yeah, we don't pay a dime."

[Bobtheduck]

Bittorrents isn't really any less reliable than any other P2P... Try finding anything worth getting on Limewire... Pretty difficult... Torrent sites are often well organized, and you can find them without porn, and there are entire sites devoted to LEGAL torrents, so you can avoid the whole warez thing. If I knew how to seed my own files, I would seed videos... Anyone can help me with that, I'd be appreciative....

[uc pseudonym]

On a more technical level, how does bittorrent work? It obviously breaks a larger file into quite a few individual packets. Does it then begin to methodically go through the list of packets until it finds one (or more) that are available? Then, once it is done, does it list that packet as available from one source on a given channel? That's just my best guess, of course.

[Mr. SmartyPants]

I love bittorrent. Though download times vastly differ. Once it took me 10 minutes to download a bleach episode. Another time it took me a about 10 days to download a season of some anime title. There weren't many seeders for it.

[Locke]

Bittorrents isn't really any less reliable than any other P2P... Try finding anything worth getting on Limewire... Pretty difficult... Torrent sites are often well organized, and you can find them without porn, and there are entire sites devoted to LEGAL torrents, so you can avoid the whole warez thing. If I knew how to seed my own files, I would seed videos... Anyone can help me with that, I'd be appreciative....

Just leave the torrents in the window once it finishes and you'll start seeding.

Oh and what kind of torrenter do you guys use? I still use the default Bitorrent one, is this good or would other programs speed up the download process?

[LorentzForce]

On a more technical level, how does bittorrent work? It obviously breaks a larger file into quite a few individual packets. Does it then begin to methodically go through the list of packets until it finds one (or more) that are available? Then, once it is done, does it list that packet as available from one source on a given channel? That's just my best guess, of course.

Packets are almost meaningless in higher layers, which in this case, is application layer, since BT program does all checksum checking and validating and so forth.

Basically the file(s) are divided in chunks of some certain size, depending between higher overhead vs higher chance of error introduced (small chunks vs big chunks). The actual torrent file just contains tracker information, file names, chunks, and their checksums. User then uses the torrent file using a torrenting application, connects to tracker saying "yo I'm around". Tracker introduces them to other peers/seeds who are already there. You also tell the tracker which chunks you already have and which you don't yet.

Peers now and do two things; ask you for chunks you already have, or you get chunks you don't have off them. Seeds just let everyone grab chunks off them because they're already done. Notice how tracker merely tracks this data transfer (like who gave what to who, who joined, who is peer, seed, so on), not the actual data.

And now the usual, share the chunks, check they're right, and save, flag as done, others can get them too, and so on, until it's finished.

[Mr. SmartyPants]

Just leave the torrents in the window once it finishes and you'll start seeding.

Oh and what kind of torrenter do you guys use? I still use the default Bitorrent one, is this good or would other programs speed up the download process?

I perfer bittornado (http://www.bittornado.com)

You can change how much you upload/download, choose to download specific parts of files (If I am downloading episodes 10-16 of an anime. I can choose to get episode 10 first. Or just cancel all but 10 and 11. In case if I need those 2 again)

It also lets you see who you are connected to, their IP addresses, etc.

[Kumagoro]

Am I supposed to leave the window open once my thing is done downloading? If I delete the torrent after I've got all the pieces am I doing something bad (like stealing it from other people)? I still don't totally understand it.

[Kaligraphic]

You should leave the torrent going for a bit, because once you finish it will act as a seed and speed up other people's downloads.

[Mithrandir]

To be a "good member of the group" it is requested that you leave the file up until you have reached a share ratio of at least one. Depending on what client program you use, this may or may not be evident.

[uc pseudonym]

Typically I leave it open as long as is reasonable or as long as people are still uploading from me. With the files I generally download, there tends to be no activity after a fairly short time, so I figure I'm not robbing anyone of anything.

[Sync]

Some trackers will ban on low ratios too, if you plan on using one place a lot definitely keep your ratio higher than .6