What is Overlay Network

In 1999, exchanges of digital media objects, especially files of music, came to constitute a significant portion of Internet traffic, thanks to a new set of technologies known as peer-to-peer (P2P) file-sharing systems. The networks created by software applications such as Napster and Kazaa have made it possible for millions of users to gain access to an extraordinary range of multimedia files. However, the digital product characteristics of portability and replicability have posed great challenges for businesses that have in the past controlled the markets for image and sound recordings. ‘Peer-to-peer’ is a type of network architecture in which the various nodes may communicate directly with other nodes, without having to pass messages through any central controlling node (Whinston, Parameswaran, & Susarla, 2001). The basic infrastructure of the Internet relies on this principle for fault tolerance; if any single node ceases to operate, messages can still reach their destination by rerouting through other still-functioning nodes. The Internet today consists of a complex mixture of peer-to-peer and client-server relationships, but P2P file-sharing systems operate as overlay networks (Gummadi, Saroiu, & Gribble, 2002) upon that basic Internet structure. P2P file-sharing systems are software applications which enable direct communications between nodes in the network. They share this definition with other systems used for purposes other than file sharing, such as instant messaging, distributed computing, and media streaming. What these P2P technologies have in common is the ability to leverage the combined power of many machines in a network to achieve results that are difficult or impossible for single machines to accomplish. However, such networks also open up possibilities for pooling the interests and actions of the users so that effects emerge which were not necessarily anticipated when the network technology was originally created (Castells, 2000). In a narrow sense, P2P file-sharing systems refer to applications that exchange content over computer networks where the nodes act both as client and server machines, requesting and serving files (e.g., Kazaa, BitTorrent). In a wider sense, P2P file-sharing systems also include any application that lets peer users exchange digital content among themselves (e.g., YouTube, Flickr).