Information Technology Reference
In-Depth Information
Figure 1. Classification of computer systems
WAN, or the Internet. They can be based on the
client-server model or peer-to-peer model which
will both be discussed further in the following
sections.
“peer-to-peer” and there are only few attempts
to classify peer-to-peer technologies (Kant, Iyer,
& Tewari, 2002). In a P2P model, each node or
peer has both server and client capabilities. Thus,
each peer can store, send, and receive service
requests, data or music files to each other's peers
(Schoder & Fischbach, 2002). In addition, each
peer makes a portion of its own resources (e.g.,
part of hard disk, bandwidth, CPU) available to
other peers (Lesavich, 2002). P2P networks build
the infrastructure for the following three appli-
cations: resource sharing, virtual communities,
and for this chapter the most relevant one which
is file sharing (Schoder, Fischbach, 2002). There
are, on one hand, the centralized P2P, and on the
other hand, the decentralized P2P systems. Also
there are lots of P2P systems in between, we will
present shortly those two opposing ones.
Client-Server Model
The client-server model describes the relation-
ship between two computer programs in which
one program, the client, makes a service request
to another program, the server, which fulfils the
request. Although the client-server model idea can
be used by programs within a single computer, it
is a more important idea in network computing.
In a network, the client-server model provides
a convenient way to interconnect programs,
computers, or devices that are distributed across
different locations. This model has become one
of the central ideas of network computing and
most digital music distribution systems (Minar
& Hedlung, 2001).
Centralized Peer-to-Peer
Centralized or mediated P2P networks utilize the
client-server network structure. The server facili-
tates the interaction between peers by maintaining
directories of the shared files stored on the respec-
tive personal computers of the registered users of the
network. A centralized directory server maintains
an index with the metadata, all control and search
messages are sent to the central server. The first
type of peer-to-peer music sharing networks where
based on this structure, where the most prominent
example was Napster (Minar & Hedlung, 2001).
Peer-to-Peer Model
The idea of P2P in a network environment is
not new. In 1996 for example, a young Israeli
firm called Mirabilit launched its popular ICQ
(“I seek you”) instant messenger services using
a P2P architecture to send messages between
personal computers connected to the Internet
(Shirky, 2001). Despite its existence for several
years, there is no unique definition for the term
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