Tribler

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Tribler - P2P software has come a long way over the last few years. Skype pioneered P2P Internet telephony and Wikipedia volunteers create an encyclopedia without authoritative, central editors. With Tribler, we are creating software for video file sharing that has a basic understanding of human friendships, of user tastes in content, and of Internet connectivity between users. Currently, Tribler is not production-level software yet, but we do have a fully functional proof-of-concept.

The Bittorrent protocol designed by Bram Cohen works great and currently dominates the traffic on the Internet backbone, but it lacks many features that may be very useful. We are improving this protocol with over a dozen people with such features which go way beyond the original. We are extending the code from the ABC project.

Some of the latest features of Tribler are:

• Amazon-like recommendations to get interesting files
• Doubling the download speed by using the upload capacity of friends
• Real-time P2P file sharing with P2P video streaming
• Showing the locations of other downloaders of the same content with city-level accuracy on a world map

Behind the scenes of P2P Technology

The main idea of P2P technology is that users pool resources to create a service. Because users donate resources, the content distribution infrastructure is very cost-effective. Consumers are now beginning to use the Internet to buy content, for example, music from Apple iTunes. In the UK, the BBC uses a Bittorrent-like file-sharing system for TV program downloads. The Skype Voice Over IP software uses P2P to reduce the cost of Internet telephony and became a market leader in just a few months. P2P is now the 'killer application' of the Internet. Figures based on actual backbone measurements show that P2P is the main Internet traffic component. Astonishingly, over 60% of all Internet traffic is now P2P.

Unfortunately, P2P is currently used mainly for the illegal spreading of copyrighted files. We believe that P2P is the future of content distribution and will mature from the current 'wild west' into a respectable business solution. We focus on the technical problems of P2P, and aspects of business models such as payments and advertisements are outside our scope. Many authors have argued that P2P will create new business opportunities, for example, P.E. Geller, Kwok et al., and L. Lessig. Spreading specialized content to only a small audience, such as video recordings of local concerts, soccer matches, and city council meetings, will suddenly become feasible due to the low cost of using P2P over the Internet.

Cooperative Download - Understanding Tribler

Early downloading protocols (e.g., Gnutella) have no incentives for donating upload bandwidth. This approach has serious limitations in real environments, because unconstrained bandwidth sharing is sensitive to freeriding. The Bittorrent tit-for-tat mechanism was the first system which offered an incentive for uploading. The current Bittorrent mechanism also has its disadvantages, because without enough seeding peers, the download speed of a peer depends on its actual contribution to the community. In real systems this is overly restrictive, as Bittorrent's tit-for-tat bartering protocol limits a peer's effective download bandwidth to its upload link capacity. Hence, peers with asymmetric Internet access, such as ADSL or ADSL-2, cannot fully use their download capacity.

We have developed a new cooperative downloading protocol which makes use of social groups, where members who trust each other cooperate to improve their download performance. Peers from a social group that decide to participate in a cooperative download take one of two roles: they are either collectors or helpers (see Figure 1). A collector is the peer that is interested in obtaining a complete copy of a particular file, and a helper is a peer that is recruited by a collector to assist in downloading that file. Both collector and helpers start downloading the file using the classical Bittorrent tit-for-tat and cooperative download extensions.

Before downloading, a helper asks the collector what chunk it should download. After downloading a file chunk, the helper sends the chunk to the collector without requesting anything in return. In addition to receiving file chunks from its helpers, the collector also optimizes its download performance by dynamically selecting the best available data source from the set of helpers and other peers in the Bittorrent network. Helpers give priority to collector requests and are therefore preferred as data sources.