Peer to peer networks fall into two categories. The original meaning of this type of network was a network where it was necessary to connect a small number of physically proximate computers together at very low cost. The basic implementation of this type of network requires only a network card in each machine, and a hub or switch if more than two computers are to be connected. Providing all the computers in the network talk the same language (in other words, use the same networking protocol such as TCP/IP, and run compatible application or operating system software205, all machines on the network will be able to communicate and exchange data. Under Windows, if a machine is in a workgroup it is in a peer-to-peer network.
Most forms of networks have some type of authentication system in place to allow a degree of control over who may access the services provided. The most familiar type of authentication is the username and password model, which allows the assignment of permissions (what that user may and may not do) to each user account. As the name suggests, in peer-to-peer networks all machines are created equal and do not work together to maintain a central security model. In practice, this means that each machine on a peer-to-peer network maintains its own authentication system and security database, which is the main downfall of this type of network. When a low number of machines are involved it is relatively simple to maintain individual user account and password databases on each machine, but when the number of machines increases, it becomes exponentially harder to maintain and troubleshoot as the same person may have different usernames and passwords on each machine. As a practical example, consider how many different usernames and passwords you have for accessing various websites, FTP sites and email accounts on the Internet.
The Internet has given birth to a new form of peer-to-peer network in the latter half of the 1990s the file sharing peer-to-peer network. Commonly referred to as P2P and made famous by Napster and Kazaa, these networks are comprised of millions of computers around the world; all using the same client software to form what is effectively an impromptu peer-to-peer network across the Internet. These P2P networks differ from the traditional peer-to-peer network in a few small ways. First, they are created explicitly to share files between people206 with a degree of anonymity. Second, whilst they are peer to peer in name, most services actually use centralized servers to ensure clients can connect to the network and search for the files they need. Whilst the majority of content on these networks is illegal, the technology behind them is often quite impressive, in some cases allowing the networks to scale to millions of clients.
205. The basic requirement of any network is for hosts using it to be able to talk to each other. Whilst this does not necessitate the same operating system to be installed on all hosts, it does require that compatible software and services be installed. A good example of this is Unix and Windows hosts on the same network, with the Windows hosts using SMB file sharing and the Unix hosts running SAMBA.
206. Napster was the original MP3 file swapping service, accused by record labels of facilitating the illegal exchange of copyrighted music. It was eventually shut down on 28th July 2000, but was recently reopened as a legal music content service.
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