Introduction - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 1

Chapter 1
Introduction
1.1 Overview
Modern computing technologies have decentralized data processing power
in an unprecedented manner. An important implication is that user machines,
be it a desktop computer or a handheld PDA (personal digital assistant),
have data processing power, in terms of instruction processing rate, amount
of storage, and reliability, that was inconceivable merely a decade or two
ago. Indeed, computing now occurs largely at the “edge” of networks. Net-
work infrastructure systems have also made tremendous strides thanks to
the ever improving communications technologies. Advancements in comput-
ing and communication, coupled together, enable a recent trend in a new form
of distributed processing—peer-to-peer (P2P) computing [Oram, 2001, Stein-
metz and Wehrle, 2005, Leuf, 2002, Minar and Hedlund, 2001, Milojicic et al.,
2002, Roussopoulos et al., 2004, Schoder and Fischbach, 2003, Smith et al.,
2003].
As its name implies, P2P computing involves users (or their machines)
on equal footing—there is no designated server or client, at least in a persis-
tent sense. Every participating user can be a server and be a client depend-
ing on context. Some people have referred to this as a “democratic com-
puting environment” [Androutsellis-Theotokis and Spinellis, 2004] because
users are free from centralized authorities' control. This new paradigm of
distributed computing has spurred many high profile applications, most no-
tably in file sharing, such as: BitTorrent [Cohen, 2003], Freenet [Clarke et al.,
2000], Gnutella [Gnutella Protocol Development, 2009], and, of course, Nap-
ster [Napster, 2009].
Apart from the most commonly known wired P2P file sharing applications,
some other wireless P2P applications have become part of our daily life. For
example, people can now play numerous P2P Java online games which are
compatible with mobile phones so that players are allowed to interconnect in
local area through Bluetooth and WiFi, or wide area through 3G network.
Indeed, in many metropolitan cities such as Hong Kong and Tokyo, we can
see that train commuters routinely play wireless games among each other
using popular devices such as PSPs (Play Station Portables). Now, many
mobile phones also already have toward GB or higher RS-MMC card storage
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