Spreading of a file in a P2P system

In a peer-to-peer (P2P) file exchange system, there is no central server that would store all available files and distribute them to users. Instead, the system self-organises in a way such that exchanges occurr directly between users, between peers.

Here we represent the spreading of a file among users of such a system: each node represents a peer, and each peer is linked to the peers which provide the file to it. The dynamics consists in appearance of new nodes and links. In general, a new link arrives with links to one or several other peers, which means that they provide the file to it first. Afterwards, it may be linked to other peers because they provide the file to it, or because it itself provides the file to them.

One may observe many facts in this video. First, it clearly shows that many peers are linked to only one other, which means that they asked for the file to this peer but never provided it. This may be due to interrupted downloads, or to free-riding: it is well known that many peers refuse to provide files although they download some.

More interestingly, one may notice that we observe cascade phenomena: a peer provides the file to another one, which provides it in turn to another one, and so on. This is essential to the system, as peers generally disconnect rather rapidly, and this illustrates an important feature of peer-to-peer exchanges: even though the initial provider is not in the system anymore, the file is still available.

One may also notice that some peers appear disconnected from the others. This means that they are provider of the file when they arrive in the system: they probably downloaded it previously or elsewhere.

(New nodes and links appear in red; afterwards, the color of nodes indicates their time of arrival: the first arrived nodes are white, and then darker and darker.)

Category:

Science & Technology

Tags:

• complex networks
• p2p
• spreading

[Blazed15]

Awesome!