Webupon

The Internet offers the following services: sending and receiving e-mail (electronic mail), transferring files between computers, participating in discussion groups through newsgroups and mailing lists, searching and retrieving information, chat, Internet relay chat, instant messaging, Internet telephony (voice chat), and on-line shopping. Newsgroups contain databases of messages on topics. They are similar to mailing lists, except that e-mail messages are posted to newsgroup sites. Bulletin boards and discussion groups offer similar services. People “surf the net” to find information and download files and connect directly to other computers. Web pages are used to communicate with customers and suppliers, describe organizations and products, tender documents, and provide services (banking, stocks, and software).

Similar to most other communication breakthroughs before it, the initial media and popular reaction to the Internet has been mostly negative. For example, it has been described as “awash in pornography,” and as making people “sad and lonely.” Yet, counter to the initial claim that Internet use causes depression and social isolation, the body of evidence is mainly to the contrary. It is argued that like the telephone and television before it, the Internet by itself is not a main-effect cause of anything. Research in psychology investigates how social identity, social interaction, and relationship formation may be different on the Internet than in real life.

File sharing is emerging as an important use of the Internet. The widely-recognized peer-to-peer (P2P) file-sharing applications (e.g., Napster, Kazaa, and Emule) have gained their reputation due to the large number of people using them and because of the public controversy that has been created about whether or not their use is legal. They also have a similar impact in the research community. File-sharing applications have demonstrated that from basic peer-to-peer interactions, it is possible to dynamically create social networks within which people can collaborate by sharing and retrieving information.

Because of the popularity of Napster and its successors (Gnutella, Kazaa, Morpheus, and E-Donkey), file sharing has become the killer P2P application. Gnutella addressed Napster’s shortfall of complete decentralization, but its unstructured nature raised concerns over its search mechanism’s efficiency and scalability. In 2001, P2P applications started to use superpeers (a set of more powerful nodes in a heterogeneous network) to transform the existing flat topology of these networks into a hierarchical one. Superpeers are considered faster and more reliable than normal peers and take on server-like responsibilities. For example, in the case of file sharing, a superpeer builds an index of the files shared by its client peers and participates in the search protocol on their behalf. This improves scalability by limiting the flood of search traffic. The most successful peer-to-peer application appears to be BitTorrent.

In BitTorrent, groups of peers with the same interest in downloading a specific files cooperate to accelerate the process. Essentially, a tracker node stores a list of peers in the group, thus letting new peers join. Each peer stores pieces of the file. Cooperating peers download and upload required pieces. If a peer stops uploading, other peers will likely block it; that is, they stop uploading to it. This implements the tit-for-tat-like process. Seeders, peers that store the whole file, are crucial to a group’s functioning. If a group contains no seeders, eventually some pieces of the file might be completely missing from the group. Because peers gain nothing themselves by being seeders, the system requires some altruistic behavior from peers. This requirement is reflected by the mantra often repeated on BitTorrent Web sites: leave your download running for a little while after you’ve got the entire file.