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Last Updated: Thursday, 13 April 2006, 18:35 GMT 19:35 UK
BitTorrent battles over bandwidth
Spencer Kelly
By Spencer Kelly,
Presenter, BBC Click

Close-up of compact disc, Eyewire
Video files take much longer to upload than music files
Nowadays, many of us have a lot of media stored on our computers such as software, music, videos.

In the last few years users have started to share that content with each other across the net, whether legal or not.

This is something that has plagued the music industry for several years. And now, mainly thanks to a system called BitTorrent, the movie industry could face the same struggle.

But BitTorrent could also be the solution.

Hollywood is definitely interested in distributing its movies over the net. King Kong is the first major film in the UK to be released as a download at the same time as on DVD.

Users on the web will visit a download site and pull the data onto their computers. Many users can be served at once but, if demand is huge, users will effectively have to queue up and wait their turn.

But there is another way to get hold of content and it has caused a nightmare for the music industry of late, with users sharing content amongst themselves, their peers.

Using a peer-to-peer (P2P) file-sharing program and a decent internet connection, a user can make all his files available to anyone else who is using the same program.

If you wanted to get hold of a particular song, your file-sharing program would hunt for that file on other people's hard drives. When it finds it, it downloads a copy to your own computer.

The more users who download the file, the more places there are for other users to get it. This reduces the likelihood of bottlenecks, and is a very efficient way of distributing files across the net.

Of course, it is illegal to share copyrighted material like that. But this has not stopped people doing it.

Larger files

More recent developments include being able to download different parts of the same file from different users.

But video files are much larger than music files and have slower upload times.

This is where BitTorrent comes in. It is an incredibly efficient way of distributing large files, like video, across the net, even when there is a high demand, and even when only one person has the complete file.

The key is that a user's computer does not need to wait until it has downloaded the entire file.

As soon as it has downloaded a chunk, it starts uploading it to any other users who do not yet have that chunk.

Similarly, your computer finds other users who have chunks that you are missing, and downloads many at once.

The group of machines sharing a file is called a swarm, for obvious reasons. And the torrent of data flowing between them is called a torrent. The more people in the swarm, the faster the file spreads.

Using BitTorrent is not particularly difficult. There are many different BitTorrent programs freely available for download.

These manage the uploading and downloading for you, maximising your internet connection, which can end up shifting gigabytes in a session.

Once finished downloading, it is considered good manners to stay online, allowing the program to continue sharing the file with other users.

Broadband 'hogs'

BitTorrent's efficient use of broadband connections has hugely increased the amount of traffic going across the net, because it runs all users' net connections flat out to deliver huge files.

Recent estimates say that around a third of all internet traffic is based around BitTorrent.

Some internet service providers think this is unacceptable. Recently BT began clamping down on so-called "broadband hogs", by starting to enforce a 40GB monthly limit.

Certainly you could kind of see P2P as one of the killer applications for broadband
Jonathan Arber, Ovum
Some ISPs go even further, breaking down customers' net usage into different types of activity, and discriminating against bandwidth-hungry file-sharers.

So-called traffic-shaping is part of an ongoing battle between ISPs and BitTorrent programmers.

As network providers look for smarter ways to identify torrent traffic, and reduce its impact on their network, more and more help sites are springing up showing users how to encrypt their data to avoid it being tracked and controlled.

Bulldog is one ISP which does not feel the need to traffic shape its data flow. The company's Gavin Young says this is because there are different types of ISPs.

He told Click: "Some ISPs are what we call infrastructure-based, and that means they build their own networks.

"But other ISPs, maybe just for example a brand, are paying money for the fibre, connectivity in that network, and maybe they can't even afford to buy a whole fibre and they're just leasing per megabit units of bandwidth. You're going to be more inclined to try to shape your traffic to keep your cost base down."

Jonathan Arber, a technology expert from Ovum, who specialises in file-sharing, believes ISPs are right to be worried about the amount of traffic that something like BitTorrent creates.

He said: "Certainly, you could see P2P as one of the killer applications for broadband. What that means is that, if users find that their broadband service is actually limiting the application that they most want to use, they'll simply go somewhere else."

New approach

According to Bulldog's Gavin Young, a recent online survey which asked people how ISPs should react to P2P traffic found most respondents wanted to slow it down. In other words to traffic-shape.

He added: "Basically this is a kind of a robotic application to a lot of people.

"They don't necessarily interact that much, they might kick off a download, and go to work or whatever, and so it's not like you're surfing the web, or expecting a response or an instant message.

"If something takes three hours instead of two hours, fine. I suspect as people are doing more with video, as opposed to music and songs, that kind of kick-it-off-and-walk-away approach is going to be more common."

But instead of traffic-shaping and limiting what could be the killer application for broadband, could not an ISPs just buy more bandwidth? After all, it is their business to provide this data flow.

Mr Young explained: "Unfortunately, if you buy more bandwidth, somebody has to cover the cost of that.

"What we're seeing is ISPs introducing tiered services, so for example, given the opportunity for light users to maybe have a metered package, who pay per unit at a time or per amount of data you download. So you can control your own costs as a user, and unlimited packages will inevitably cost a bit more.

There are many programs that use the BitTorrent protocol, but it is still not a completely user-friendly experience.

Ovum's Jonathan Arber said: "The various applications, while they are getting more user-friendly, still require a degree of technical knowledge in order to really get BitTorrent working the way it should.

"If you want to kind of get the kind of download speeds that people talk about, you're going to have to know a little bit about configuring the application, a little bit about configuring your own network as well."

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