BitTorrent

BitTorrent is a file swarming app that allows you to download massive files pretty quickly. Unlike other apps like this, it works from your browser, you click on a link from a bittorrent page, and it asks where you want to save it. After that, you simply sit and watch as the file downloads. The mechanics of all this are beyond me, perhaps someone could expand on this? - Tsunami

So, what actual real legitimate uses are there out there? Not 'oh well it could be helpful to do...' but actual real installations that aren't mainly concerned with illegal activity?

I'm sure there must be some.. mustn't there? Like maybe free software installation images? --ChiarkPerson

To get the obligatory bit out of the way with: for the purposes of answering the question, let's assume that one is counting anime fansubs as (technically accurately) illegal, or (for some reason) illegitimate, or just uninteresting. Anything else? --AC

Instant use springs to mind: installing Linux distributions (typically a few Gb); downloading kernel updates (typically a few tens of megabytes), CD-ROM images and package updates (and, heck, new packages). One might have to tweak the trust model a little, though. Oh, and for that matter things like film trailers. Sites like http://www.mp3.com could use it, at a pinch. Any time anyone wants to publish something bigger than a megabyte or two, it becomes worth it, basically. - MoonShadow

I think the question is about actual current uses, though, not potential ones. Anyone know anything it's currently being used for that's not technically illegal? --AC

These are mostly current. RedHat ISOs were being distributed right from the start. Google: bittorrent says [lots] of linux stuff is being distributed that way these days. Oh, here's some[trailers].. is that enough? - MoonShadow

: Just to add - GameTab? is great. Game demo's are getting silly in terms of download size - and the servers couldn't keep up. Enter FilePlanet? in an attempt to extort money from free releases. Enter BitTorrent in an attempt to, you know, not. --Vitenka
: And WizardsOfTheCoast are now distributing videos of MagicTheGathering ProTour? finals via BitTorrent: see the bottom of [this article]. --AC

If you came here from a search engine looking for a list of bittorrent trackers for anime fansubs, try [here] or [here].

Animesuki.com appears to be out at the moment... Anyone have the address of a mirror to hand? --Kazuhiko

No such animal, AFAIK. http://anime.mircx.com/ not listing what you're after? - MoonShadow

I thought after all the DDoS on animesuki they put mirrors in place? Ah well. I'm getting RoD TV from mircx but I'll wait for the sub-groups I recognise on animesuki for other stuff I think --Kazuhiko

: Ah - I hadn't spotted that ^^; Google's cache gives http://animesuki.sandwich.net/mirrors.php - which seems to work. - MoonShadow

This page got popular quick. Heh - looks like BitTorrent is coming out from being EarlyAdopters? only, and moving to be more mainstream.
So [Here is a better windows gui client] and [Here are some decent instructions for getting started]

Uh - do bear in mind that the [original] author of bittorrent spent a long time optimising the client, and current third-party clients generally make bad choices (bandwidth allocation, where to get what pieces and so on) that result in decreased efficiency. So to some extent there's a tradeoff between having a pretty gui and actually making good use of your bandwidth. - MoonShadow

That client is based off of the latest (3.2.1 at time of this writing) official version. Really, all it does is add some bells and whistles to the front end and help you set some settings graphically rather than using command line switches. Yes, some of those settings would be a bad thing to set - but it does warn you against them. Basically, set the upload bandwidth to just a tiny bit less than the maximum your connection gives you, and watch it fly. --Vitenka

: There is now a new official version (3.3), which claims to feature performance improvements. This may affect the above. -- TI

I'll correct this now. The client you really want to use is the main bittorrent client from cvs. The windows installer hasn't been updated in aaaages - but the cvs includes all the good stuff you want. (Including working --max_upload_rate switches) --Vitenka

There are now, I believe, a few different BitTorrent clients for the windows environment. Does anyone have any recommendations? --K

[ABC] (short for "yet Another BitTorrent Client") does queue multiple downloads and lets you specify conditions to quit after a download has finished, possibly specifying a time to wait first. It also supports having a default downloads directory - so clicking torrents from webpages becomes zero-interaction, so you can go "click torrent 1, pause, click torrent 2, pause, click torrent 3" to enqueue three torrents. It will quit one download and start the next in the queue after either a certain time or a certain share rating. It's been very nice from the time I've used it. My only complaint is that it seems to pretty much ignore your settings for maximum upload bandwidth, so you have to set the other limits and behaviours on the cautious side to prevent it drowning your ACK packets and thus getting next-to-no download speed. But even with that said, it's magnificent and there's no way I'd go back to the old client given the choice. --AlexChurchill

BitTorrent is a P2P application - though it uses a central server to administer things.

Swarming clients are a GOOD thing.
Although it doens't "work from your browser" - your browser downloads a .torrent file, which gives the URL of the tracker, details on the file, CRC etc. It then passes this on to the bittorrent application, which handles the rest.

The process works as follows:

First bittorrent prepares the file you are about to recieve. It checks each block of it to see if you have already downloaded it (this is to support resuming) and then tells the tracker 'new client here, I have these blocks and I need these)

Then it is given a list of other clients, and contacts each of them asking for the blocks it wants.
Once it has ANY blocks, it can then provide them to other clients which ask for them.

Once it has the complete file, it can stop - but if you are nice, you leave the client open - providing the file to other people.

Importantly, which order your client gets blocks in (and hence which order it can provide them in) is randomised - so that you never get into a situation where every client has the first four blocks, but only one overloaded seed node can feed any more.

Obviously, for a bittorrent to work, you need to have a central tracker - and at least one active client which has the whole file (which is referred to as the seed)

The advantage for the seed is that it can limit downloads to an arbitary number of clients at once - and yet still be assured that if more than one person attempts to download the file, they will be able to get it (from each other)

I find, in practice, that only seconds after I have started a download, I am uploading at my maximum rate. This suggests MOST people have a limited uprate (compared to their downrate)

The application also engages in tit-for-tat. If you upload to a client at only 1k/s, it will upload to you at 1k/s. This way most people enable uploading at a decent rate - allowing your total download rate to be silly.

This is a good theory. However, since BT have taken to capping our upstream bandwidth by dropping our connection, I have been setting upload limits on my client (fairly recent Python script; basically, whatever's in debian testing these days) at 1-2kbps. Incoming data on even vaguely popular torrents still saturates my pipe, even though I can prove to my own satisfaction that the upstream bandwidth is being throttled. Still, I'm not complaining or anything :) - Moon "inadvertent leech" Shadow

: Agreed - seeds (which have nothing remaining to download) tend to saturate anyone they see. And for some reason Bram refuses to consider adding downrate limiting. --Vitenka

Sadly - the windows client is extremely badly behaved - it tends to keep socket descriptors for way longer than it should. This leads (inevitably) to 'out of resources' errors, no other application being able to access the net, etc. Restarting bittorrent (it cleanly resumes) fixes this, but it is annoying. Then again, the windows client is very beta.

For more details - the official [Protocol Specification]

Oh, I should add one problem with the bittorrent system. It can only work if:

The tracker is still online
At least one seed node is up.

There seem to be few, stable trackers so far - and it's hard to find a seed for anything more than a few weeks old (but not impossible any more). Which means bittorrent links are fairly strictly time limited. This will probably change, as more and more websites cotton on to the advantages of bittorrent for ANY download and integrate it with their webservers. Oddly, the protocol doesn't allow a tracker to deny arbitary files - though I'm sure someone will fix this once more people start abusing each others trackers. Though the tracker does not need much bandwidth - it does need a LOT of connections and a stable DNS.
People are starting to seed older files - and to do so with huge collections of files. These collections, being large, stay active on the trackers for longer. There are also better clients coming along, which automatically add themselves as a seed when they see a request coming in.

http://anime.mircx.com/ is currently down as of 11 June 04 as they have been asked not to post links to licenced shows. --Tsunami

CategoryComputing CategoryWeb