Peer+to+Peer

__Description__:
Peer to peer networks first made their apparition in the late 70's early 80's with USENET and FidoNet. At that time there was a strong need for decentralization in network architecture. On the Internet, peer-to-peer (referred to as P2P) is a type of transient Internet network that allows a group of computer users with the same networking program to connect with each other and directly access files from one another's hard drives.

In the Peer-to-Peer model all computers, or nodes, share resources. Opposed to the client/server model, all clients on the P2P model share resources including bandwith, computing capability, and data. As the number of clients increase so does the capability of the network. While in the client/server model more users would decrease the efficiency of the network.

Peer-to-peer is a very easy to use network. It really facilitates team work and the way it is designed makes it real secure due to the fact that all the data are shared among many peers. Also, Peer-to-Peer is a communications model in which each party has the same capabilities and either party can initiate a communication session. Other models with which it might be contrasted include the [|client/server] model and the [|primary/secondary] model.

In computer networking, master/slave (primary/secondary) model is a model for a communication protocol in which one device or process (known as the //master//) controls one or more other devices or processes (known as //slaves//). Once the master/slave relationship is established, the direction of control is always from the master to the slave(s). The County of Los Angeles, saying the term master/slave may be offensive to some of its residents, has asked equipment manufacturers not to use the term. Some manufacturers prefer the term '__primary/secondary__'.

In a client/server network architecture all the data are stored in a server. If something happens to the server there is a risk of loss of data. In the client/server model the server program responds to requests from a client program, and the peer-to-peer model either of the two devices involded (client) can initiate a communication session.



In some cases, peer-to-peer communications is implemented by giving each communication node both server and client capabilities. In recent usage, peer-to-peer has come to describe applications in which users can use the Internet to exchange files with each other directly or through a mediating server.

Note Well: IBM's Advanced Peer-to-Peer Networking (APPN) is an example of a product that supports the peer-to-peer communication model.

**How Does Internet P2P Work?**
The user must first download and execute a peer-to-peer networking program. (Gnutellanet is currently one of the most popular of these decentralized P2P programs because it allows users to exchange all types of files.) After launching the program, the user enters the IP address of another computer belonging to the network. (Typically, the Web page where the user got the download will list several IP addresses as places to begin). Once the computer finds another network member on-line, it will connect to that user's connection (who has gotten their IP address from another user's connection and so on). Users can choose how many member connections to seek at one time and determine which files they wish to share or password protect.

Different types of P2P network
There are different types of P2P network that all have several different applications. For example we can identify these following types: affinities communities, instant messaging, collaborative… (will describe the different types in details soon)

Advantages
The chief advantage of peer-to-peer networks is that large numbers of people share the burden of providing computing resources (processor time and disk space), administration effort, creativity, and--in more than a few cases--legal liability. Furthermore, it's relatively easy to be anonymous in such an environment, and it's harder for opponents of your peer-to-peer service to bring it down. Corporations are looking at the advantages of using P2P as a way for employees to share files without the expense involved in maintaining a centralized server and as a way for businesses to exchange information with each other directly.

Disadvantages
The primary disadvantage of peer-to-peer systems, as anyone will attest who's had an MP3 download prematurely terminated when a dialup user went offline will attest, is the tendency of computers at the edge of the network to fade in and out of availability. Accountability for the actions of network participants is a potential problem, too. Searches on peer-to-peer networks may not reach and uncover all available files because search requests may not be transmitted to every computer on the network. There may be redundant copies of popular files. The creator of the software has no incentive to minimize storage or band- width consumption, the costs of which are borne by every user of the network. Most relevant here, it is more difficult to control the content of files available for retrieval and the behavior of users.

One of P2P biggest threats is the introduction of viruses and other malicious content. While the P2P service itself is a target, the users who use the service is also a target. Many people share files between eachother, but there are those who share malicious things with the intent to harm your computer. Many viruses and trojans get installed on many peoples machines without them even knowing it. A quite popular trick in the network is to replace file names. Many replace their malicious content on the P2P network with the same name as legitimate content. The pretty computer savvy people are most likely the ones that not going to be fooled, but to the novice user, its almost a dead giveaway. Some P2P clients such as emule and bearshare use tools to combat the problem. Bearshare uses a kind of community watch (via BitziTicket) in which it leaves it up to its users to report bad or fake files while emule uses a built in hash technique that stores a files' hash string so even if the filename is changed, the original file could still be recognized.

__Applications__:
>> >> > >>
 * **[|eDonkey]**: The eDonkey network is the most popular file-sharing network, surpassing the FastTrack network's userbase in 2004. The official eDonkey client was shut down in September, 2006, but the more popular eMule client still exists and is widely used.
 * **[|Napster]**: Locate and download your favorite music in MP3 format.
 * **[|**Gnutella**:]** Software tool to bypass Internet service providers and allow computer users to search and communicate directly among themselves.
 * **[|KaZaA]**: peer-to-peer (p2p) application for finding, downloading, playing and sharing files with millions of other users.
 * **[|iMesh]**: file sharing software with lots of features and services.
 * [|**Lime Wire**] File sharing (audio, videos, images, documents and programs)
 * [[image:http://www.limewire.com/img/40screenshot.png width="271" height="180"]]
 * **BitTorrent**: A different take on p2p networks, BitTorrent allows for higher speeds by breaking files up into tiny pieces which allows users who have not completeled their download to begin uploading immediately.

__Links__:
===[|http://www.webopedia.com], [|http://searchnetworking.techtarget.com] , http://www.amazon.com/Peer-Peer-Harnessing-Disruptive-Technologies/dp/059600110X ...===