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\section{Centralized} |
\section{Centralized} |
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Napster\footnote{We decided to include Napster in this section only because it has |
Napster\footnote{We decided to include Napster in this section only because it has |
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historical value (see previous section).} \cite{yang02comparinghybrid} was designed to allow |
historical value (see previous section).} \cite{napsterurl} was designed to allow |
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people to share music. It was a hybrid Peer-to-Peer file-sharing system, i.e., the search |
people to share music. It was a hybrid Peer-to-Peer file-sharing system, i.e., the search |
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index was centralized and the distribution of storage and serving of files was distributed. |
index was centralized and the distribution of storage and serving of files was distributed. |
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Peers in the Napster network made requests to the central directory server to find |
Peers in the Napster network made requests to the central directory server to find |
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\section{Loosely structured} |
\section{Loosely structured} |
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Gnutella \cite{ripeanu02mappinggnutella} is a well-known example of loosely structured overlay network. Gnutella |
Gnutella \cite{gnutellaurl} is a well-known example of loosely structured overlay network. Gnutella |
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is a pure Peer-to-Peer network as no peer is more important than any other peer in the network. |
is a pure Peer-to-Peer network as no peer is more important than any other peer in the network. |
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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 |
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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} |
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illustrates how peers form an overlay network. Initially, peer 1 creates the overlay, since |
illustrates the overlay network of Gnutella network. The Gnutella network can be considered as a variation of \emph{scale-free |
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it is the first participating peer. Then, repeatedly new peers join the network and connect to |
graph}. In scale-free graphs (also known as power-law graphs) only a few peers have high number of neighbor |
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other peers randomly. Thus, Gnutella can be considered as a variation of \emph{scale-free |
links and the majority of peers have low number of neighbor links. |
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graph}\footnote{In scale-free graphs (also known as power-law graphs) only a few peers have high number of neighbor |
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links and the majority of peers have low number of neighbor links.}. |
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\begin{figure} |
\begin{figure} |
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\centering |
\centering |