Core Concepts in Peer-to-Peer Networking

This chapter reviews core concepts of peer-to-peer (P2P) networking. It highlights the management of resources, such as bandwidth, storage, information, files, and processor cycles based on P2P networks. A model differentiating P2P infrastructures, P2P applications, and P2P communities is introduced. This model provides a better understanding of the different perspectives of P2P. Key technical and social challenges that still limit the potential of information systems based on P2P architectures are discussed. 2 Schoder, Fischbach and Schmitt Copyright © 2005, Idea Group Inc. Copying or distributing in print or electronic forms without written permission of Idea Group Inc. is prohibited. Introduction Peer-to-peer (P2P) has become one of the most widely discussed terms in information technology (Schoder, Fischbach, &Teichmann, 2002; Shirky, Truelove, Dornfest, Gonze, & Dougherty, 2001). The term peer-to-peer refers to the concept that in a network of equals (peers) using appropriate information and communication systems, two or more individuals are able to spontaneously collaborate without necessarily needing central coordination (Schoder & Fischbach, 2003). In contrast to client/server networks, P2P networks promise improved scalability, lower cost of ownership, self-organized and decentralized coordination of previously underused or limited resources, greater fault tolerance, and better support for building ad hoc networks. In addition, P2P networks provide opportunities for new user scenarios that could scarcely be implemented using customary approaches. This chapter is structured as follows: The first paragraph presents an overview of the basic principles of P2P networks. Further on, a framework is introduced which serves to clarify the various perspectives from which P2P networks can be observed: P2P infrastructures, P2P applications, P2P communities. The following paragraphs provide a detailed description of each of the three corresponding levels. First, the main challenges—namely, interoperability and security—of P2P infrastructures, which act as a foundation for the above levels, are discussed. In addition, the most promising projects in that area are highlighted. Second, the fundamental design approaches for implementing P2P applications for the management of resources, such as bandwidth, storage, information, files, and processor cycles, are explained. Finally, socioeconomic phenomena, such as free-riding and trust, which are of importance to P2P communities, are discussed. The chapter concludes with a summary and outlook. P2P Networks: Characteristics and a Three-Level Model The shared provision of distributed resources and services, decentralization and autonomy are characteristic of P2P networks (M. Miller, 2001; Barkai, 2001; Aberer & Hauswirth, 2002, Schoder & Fischbach, 2002; Schoder et al., 2002; Schollmeier, 2002): 1. Sharing of distributed resources and services: In a P2P network each node can provide both client and server functionality, that is, it can act as both a Core Concepts in Peer-to-Peer Networking 3 Copyright © 2005, Idea Group Inc. Copying or distributing in print or electronic forms without written permission of Idea Group Inc. is prohibited. provider and consumer of services or resources, such as information, files, bandwidth, storage and processor cycles. Occasionally, these network nodes are referred to as servents—derived from the terms client and server. 2. Decentralization: There is no central coordinating authority for the organization of the network (setup aspect) or the use of resources and communication between the peers in the network (sequence aspect). This applies in particular to the fact that no node has central control over the other. In this respect, communication between peers takes place directly. Frequently, a distinction is made between pure and hybrid P2P networks. Due to the fact that all components share equal rights and equivalent functions, pure P2P networks represent the reference type of P2P design. Within these structures there is no entity that has a global view of the network (Barkai, 2001, p. 15; Yang & Garcia-Molina, 2001). In hybrid P2P networks, selected functions, such as indexing or authentication, are allocated to a subset of nodes that as a result, assume the role of a coordinating entity. This type of network architecture combines P2P and client/server principles (Minar, 2001, 2002). 3. Autonomy: Each node in a P2P network can autonomously determine when and to what extent it makes its resources available to other entities. On the basis of these characteristics, P2P can be understood as one of the oldest architectures in the world of telecommunication (Oram, 2001). In this sense, the Usenet, with its discussion groups, and the early Internet, or ARPANET, can be classified as P2P networks. As a result, there are authors who maintain that P2P will lead the Internet back to its origins—to the days when every computer had equal rights in the network (Minar & Hedlund, 2001). Decreasing costs for the increasing availability of processor cycles, bandwidth, and storage, accompanied by the growth of the Internet have created new fields of application for P2P networks. In the recent past, this has resulted in a dramatic increase in the number of P2P applications and controversial discussions regarding limits and performance, as well as the economic, social, and legal implications of such applications (Schoder et al., 2002; Smith, Clippinger, & Konsynski, 2003). The three level model presented below, which consists of P2P infrastructures, P2P applications, and P2P communities, resolves the lack of clarity in respect to terminology, which currently exists in both theory and practice. Level 1 represents P2P infrastructures. P2P infrastructures are positioned above existing telecommunication networks, which act as a foundation for all levels. P2P infrastructures provide communication, integration, and translation functions between IT components. They provide services that assist in locating 4 Schoder, Fischbach and Schmitt Copyright © 2005, Idea Group Inc. Copying or distributing in print or electronic forms without written permission of Idea Group Inc. is prohibited. and communicating with peers in the network and identifying, using, and exchanging resources, as well as initiating security processes such as authentication and authorization. Level 2 consists of P2P applications that use services of P2P infrastructures. They are geared to enable communication and collaboration of entities in the absence of central control. Level 3 focuses on social interaction phenomena, in particular, the formation of communities and the dynamics within them. In contrast to Levels 1 and 2, where the term peer essentially refers to technical entities, in Level 3 the significance of the term peer is interpreted in a nontechnical sense (peer as person).