Peer To Peer Networks

This month we are looking at peer to peer networks and online file sharing. Over the last few years there has been an explosion in the usage and growth of online file sharing.

Many people assume that when talking about file sharing and peer to peer distribution in particular, something illegal must be being exchanged, downloaded, or uploaded. This doesn't have to be the case, and there are plenty of legal reasons to want to utilise the power of peer to peer networks to share files. Let's start with a few definitions:

Download:

This is the retrieval of a file across a network, grabbing the data bit by bit.

Upload:

This is the sending of a file across a network, making it available to someone else for download.

Client/server:

The client server model for file sharing is simple - a file is hosted by a server, with a defined protocol specified to be able to access and retrieve it. The world wide web largely functions like this - as a client, you request a web page, and the server which is hosting it serves it up and returns it to you. This is a centralised model, the resource exists at a single location as far as the client is concerned, and is not generally available across a number of distributed hosts.

Peer:

This is both a client and a server in the peer to peer distribution model of file sharing. The peer is a client first of all, obtaining the requested file usually in pieces, or chunks. However as each piece is obtained, the peer then acts as a server, serving up that chunk to other peers wishing to obtain it. In this way, the expansion of a files' growth is exponential - the more people that download it, the more available the file becomes, and as such it generally becomes quicker to download.

Decentralised:

We mentioned centralised above as the client/server model - decentralised refers to a peer to peer network of distributed hosts, making any hosted file available across a number of different locations. Ultimately, each user downloading the file also becomes a host for that file, effectively decentralising where the file originated from and is hosted.

As you can see, the power of peer to peer file sharing is its ability to provide almost limitless availability and bandwidth for obtaining a file, with the users who download a file providing the resources needed to host it and allowing other users to also download it. This cuts down on bandwidth costs for companies and organisations hosting large files, as the file only has to be hosted once before it is then shared amongst the peers downloading it. An example of a good usage of peer to peer networks to distribute files is the hosting of many operating system distribution images. Nowadays these images may total 3 or 4 GB of data, and while often available using the centralised client/server model, often the easiest and fastest way to obtain these files is using a peer to peer network, sharing the file for others as you download.

The disadvantage of using peer to peer networks is that instead of simply downloading and retrieving a file, a user generally has to upload part of the file as well, usually at the same time. Many networks/applications used for file sharing place a download limitation on the user if they refuse or limit their uploading capability, as they are effectively taking advantage of the peer to peer network, but not contributing towards it.

Finally, it's worth briefly mentioning the legal complications of file sharing - because as soon as you start downloading a file, you effectively then begin to host it for others. As such, when downloading copyrighted files for which you don't have permission, the biggest legal problem is that you then are hosting this file for others, also without permission.

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