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Last Updated: Friday, 31 August 2007, 10:21 GMT 11:21 UK
File-sharers forced to play fair
By Colin Barras
Technology reporter

Close-up of PlayStation controller, Sony
Tribler has also been made to work with the PlayStation 3
Researchers have found a way to enforce good manners on file-sharing networks by treating bandwidth as a currency.

The team has created a peer-to-peer system called Tribler in which selfless sharers earn faster upload and download speeds but leechers are penalised.

The technology is being assessed by a European broadcasting body looking at ways of piping TV across the net.

Tribler has also been used to turn Sony's PlayStation 3 into a video-sharing device.

Fair sharing

While file-sharing networks are good ways to help lots of people get hold of large files often they have far more people taking from the system than they do giving.

Peer-to-peer networks can become sluggish if too many users download content without sharing with others.

Using bandwidth as a kind of currency helps to encourage better habits said Dr Johan Pouwelse, an assistant professor at Delft University of Technology and co-creator of Tribler.

Dr Pouwelse has been working with associate professor David Parkes from Harvard University to add an accounting system to Tribler to encourage users to upload as often as they download.

"In our model your TV would use "TV watching minutes", our form of P2P currency, to download content," said Dr Pouwelse.

"The TV would connect directly to the internet and provide video on demand in HDTV quality.

"After you watch a program on TV, the system would automatically share this program during the night with other people, until your 'TV watching minutes' credit is healthy again," he said.

"If we get this right, it would mean quite a change in the TV business," said Dr Pouwelse.

UK currency, Eyewire
Using bandwidth as a currency helps make sharing fairer
Using bandwidth as a currency can remove some of the problems seen in file-sharing systems such as BitTorrent, said Dr Parkes.

"In peer-to-peer, I can build up credit by offering upload capacity and then use the credit for download in the future," he said.

"There is still a balance, but the balance is on the order of days rather than seconds and this time-shifting can be welfare enhancing, said Dr Parkes.

Future proof

Tribler has already caught the attention of the European Broadcasting Union (EBU), which is trying to create a standardised internet broadcasting system across Europe.

"Tribler is a good candidate," said Franc Kozamernik, senior engineer at the EBU.

"We are in the process of testing it and checking whether it fulfils our requirements or not," he said.

The EBU has already tested a number of other P2P systems and is in the process of building a media portal which will allow EBU members to publish their radio and television channels across Europe.

Overlaid on Tribler is social networking technology that helps to police the system and encourage fair sharing.

A passionate community was as effective at policing content as a central administrator, said Dr Pouwelse.

"I was doing research back in 1999 looking at an obscure website called Slashdot," he said. "It was a technology-related news website controlled by volunteers and it actually worked. A few people would post bad things but 99% of users were nice."

Peers can "gossip" or report on the behaviour of malicious users.

And because content is not stored on a central server, it is harder for malicious users to attack a P2P network, said Dr Pouwelse.

"One user cannot bring the network as a whole down," he said. "Just as the electric grid has no central elements, Tribler has no central element and should be more robust.

"The only danger is what is sometimes called a 'cascading failure'. It happened to Skype a few days ago. But in four years, Skype broke down just once."

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