p2p networks

Topics: Peer-to-peer, Gnutella, File sharing Pages: 46 (11971 words) Published: October 18, 2013
Peer-to-Peer Networks for Content Sharing
Choon Hoong Ding, Sarana Nutanong, and Rajkumar Buyya
Grid Computing and Distributed Systems Laboratory,
Department of Computer Science and Software Engineering,
The University of Melbourne, Australia
(chd, sarana, raj)@cs.mu.oz.au

ABSTRACT
Peer-to-peer (P2P) systems are popularly used as “file-swapping” networks to support distributed content sharing. A number of P2P networks for file sharing have been developed and deployed. Napster, Gnutella, and Fasttrack are three popular P2P systems. This chapter presents a broad overview of P2P computing and focuses on content sharing networks and technologies. It also emphasizes on the analysis of network topologies used in popular P2P systems. In addition, this chapter also identifies and describes architecture models and compares various characteristics of four P2P systems—Napster, Gnutella, Fasttrack, and OpenFT.

Keywords: Peer-to-Peer Networks, Distributed Content Sharing, Distributed Systems, Internet File Sharing, Fasttrack, Gnutella, Napster, and OpenFT.

1. INTRODUCTION
Peer-to-peer (P2P) content sharing technologies like Napster, Gnutella, and Kazaa are applications that have been astonishingly successful on the Internet. P2P has gained tremendous public attention through Napster which is a system supporting music sharing on the Web. It is an emerging and interesting research technology with a promising product base.

Intel P2P working group gave the definition of P2P as "The sharing of computer resources and services by direct exchange between systems" (Kan, 2001). This thus gives P2P systems two main key characteristics:

• Scalability: there is no algorithmic, or technical limitation of the size of the system, e.g. the complexity of the system should be somewhat constant regardless of number of nodes in the system.

• Reliability: The malfunction on any given node will not effect the whole system (or maybe even any other nodes).
File sharing networks like Gnutella is a good example of scalability and reliability. In Gnutella, peers are first connected to a flat overlay network, in which every peer is equal. Peers are connected directly without the need of a master server's arrangement and the

malfunction of any node does not cause any other nodes in the system to malfunction as well.
P2P can be categorized into two groups classified by the type of model: pure P2P, and hybrid P2P. Pure P2P model, such as Gnutella and Freenet, does not have a central server. Hybrid P2P models, such as Napster, Groove and Magi, employs a central server to obtain meta-information such as the identity of the peer on which the information is stored or to verify security credentials. In a hybrid model, peers always contact a central server before they directly contact other peers.

2. P2P Networks Topologies
According to (Peter, 2002), all P2P topologies, no matter how different they may be, will have one common feature. All file transfers made between peers are always done directly through a data connection that is made between the peer sharing the file and the peer requesting for it. The control process prior to the file transfer, however, can be implemented in many other ways. As stated by (Minar, 2001), P2P file sharing networks can be classified into four basic categories: the centralized, decentralized, hierarchical and ring systems. Although these topologies can exist on their own, it is usually the practice for distributed systems to have a more complex topology by combining several basic systems to create, what is known now as hybrid systems. We will give a brief introduction to the four basic systems and later delve deeper into the topic of hybrid systems.

2.1 Centralized Topology
The concept of a centralized topology shown in Figure 1 is very much based on the traditional client/server model. A centralized server must exist which is used to manage the files and user databases of multiple peers that log onto it...

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