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revision 1.141 by hemppah, Thu Mar 13 13:34:55 2003 UTC revision 1.142 by hemppah, Thu Mar 13 13:47:15 2003 UTC
# Line 87  and connecting to each other directly. A Line 87  and connecting to each other directly. A
87  Peer-to-Peer improves scalability and avoids single points of failure.  Peer-to-Peer improves scalability and avoids single points of failure.
88    
89  There are many definitions of Peer-to-Peer networks. Schollmeier \cite{schollmeier01p2pdefinition}  There are many definitions of Peer-to-Peer networks. Schollmeier \cite{schollmeier01p2pdefinition}
90  describes a Peer-to-Peer system as a system of  describes Peer-to-Peer system as a system of
91  distributed entities that share their own services. Thus, Peer-to-Peer systems can be characterized as distributed  distributed entities that share their own services. Thus, Peer-to-Peer systems can be characterized as distributed
92  systems in which all communication is symmetric and all participants entities have similar  systems in which all communication is symmetric and all participants entities have similar
93  capabilities and responsibilities. Each entity, i.e., \emph{peer}, may contribute services  capabilities and responsibilities. Each entity, i.e., \emph{peer}, may contribute services
# Line 132  In chapter 6, we present conclusions and Line 132  In chapter 6, we present conclusions and
132    
133    
134  \chapter{Peer-to-Peer architectures}  \chapter{Peer-to-Peer architectures}
135  In this chapter we will give brief history and overview of Peer-to-Peer networks,  In this chapter we will give a brief history and overview of Peer-to-Peer networks,
136  review most important Peer-to-Peer algorithms and list key differences between  review most important Peer-to-Peer algorithms and list key differences between
137  two main approaches.  two main approaches.
138    
# Line 149  both of Peer-to-Peer concept and the Int Line 149  both of Peer-to-Peer concept and the Int
149  In subsequent years, the Internet became more restricted to client--server based  In subsequent years, the Internet became more restricted to client--server based
150  applications. In recent years, however, Peer-to-Peer systems have again emerged  applications. In recent years, however, Peer-to-Peer systems have again emerged
151  room in computing world. Indeed, Peer-to-Peer has had significant social and technical  room in computing world. Indeed, Peer-to-Peer has had significant social and technical
152  attention in academia, industry and media. Already deceased Napster \cite{napsterurl},  attention in academia \cite{projectirisurl}, industry \cite{p2pworkinggroup},
153    \cite{jxtaurl}. Already deceased Napster \cite{napsterurl},
154  launched in 1999, was a new starting point for modern Peer-to-Peer computing. After  launched in 1999, was a new starting point for modern Peer-to-Peer computing. After
155  Napster, hundreds of Peer-to-Peer systems have been developed and proposed.  Napster, hundreds of Peer-to-Peer systems have been developed and proposed.
156    
# Line 164  regard to OSI model. Line 165  regard to OSI model.
165  \label{fig:application_level}  \label{fig:application_level}
166  \end{figure}  \end{figure}
167    
168  Compared to ARPA Net's Peer-to-Peer functionality, modern Peer-to-Peer systems  Compared to ARPANET's Peer-to-Peer functionality, modern Peer-to-Peer systems
169  are ad-hoc, i.e., peers join and leave the system constantly in a dynamic manner. This  are ad hoc, i.e., peers join and leave the system constantly in a dynamic manner. This
170  fact constitutes challenging requirements for efficient construction and maintenance  fact constitutes challenging requirements for efficient construction and maintenance
171  of the overlay network. Even more demanding tasks are how to perform efficient data  of the overlay network. Even more demanding tasks are how to perform efficient data
172  lookup and maintain security in a varying distributed environment. The most popular  lookup and maintain security in a varying distributed environment. The most popular
# Line 177  more resources from others. This can be Line 178  more resources from others. This can be
178  In a development of modern Peer-to-Peer systems, lot of influences has been attained from  In a development of modern Peer-to-Peer systems, lot of influences has been attained from
179  other research areas than computer science. Research has been conducted regarding  other research areas than computer science. Research has been conducted regarding
180  to self-organizing nature of complex networks \cite{albert-02-statistical}, \cite{albert-00-tolerance}, \cite{watts00dynamics}.  to self-organizing nature of complex networks \cite{albert-02-statistical}, \cite{albert-00-tolerance}, \cite{watts00dynamics}.
181  It's interesting to realize that chemical properties of cells, the Internet, ad-hoc  It's interesting to realize that chemical properties of cells, the Internet, ad hoc
182  Peer-to-Peer systems, and social networks have all in common that they self-organize based on same  Peer-to-Peer systems, and social networks have all in common that they self-organize based on same
183  principles.  Furthermore, the association between social relationships among people  principles.  Furthermore, the association between social relationships among people
184  and Peer-to-Peer overlay topology has been studied recently  \cite{watts00dynamics},  and Peer-to-Peer overlay topology has been studied recently  \cite{watts00dynamics},
# Line 214  directory, and had a single point of fai Line 215  directory, and had a single point of fai
215    
216  Gnutella \cite{gnutellaurl} is a well-known example of loosely structured overlay network. As in  Gnutella \cite{gnutellaurl} is a well-known example of loosely structured overlay network. As in
217  other Peer-to-Peer networks, no peer is more important than any other peer in the network.  other Peer-to-Peer networks, no peer is more important than any other peer in the network.
218  The construction and maintenance of Gnutella network is extremely ad-hoc, since participating  The construction and maintenance of Gnutella network is extremely ad hoc, since participating
219  peers can form the overlay network based on \emph{local} knowledge. Figure \ref{fig:gnutella_overlay}  peers can form the overlay network based on \emph{local} knowledge. Figure \ref{fig:gnutella_overlay}
220  illustrates how peers form an overlay network. Initially, peer 1 creates the overlay, since  illustrates how peers form an overlay network. Initially, peer 1 creates the overlay, since
221  it's the first participating peer. Then, repeatedly new peers join the network and connect to  it's the first participating peer. Then, repeatedly new peers join the network and connect to
# Line 225  links and major of peers have low number Line 226  links and major of peers have low number
226  \begin{figure}  \begin{figure}
227  \centering  \centering
228  \includegraphics[width=6cm, height=6cm]{gnutella_overlay.eps}  \includegraphics[width=6cm, height=6cm]{gnutella_overlay.eps}
229  \caption{Gnutella's loosely structured ad-hoc connectivity graph.}  \caption{Gnutella's loosely structured ad hoc connectivity graph.}
230  \label{fig:gnutella_overlay}  \label{fig:gnutella_overlay}
231  \end{figure}  \end{figure}
232    

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