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loosely. The placement of services and topology of the overlay is random. The data lookup model in loosely structured systems is |
loosely. The placement of services and topology of the overlay is random. The data lookup model in loosely structured systems is |
180 |
not very efficient, because of unstructured properties of the overlay. |
not very efficient, because of unstructured properties of the overlay. |
181 |
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182 |
\subsection{Sketch of a formal definition} |
\subsection{Definition} |
183 |
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184 |
In this subsection we formalize loosely structured overlay's main components. This |
In this subsection we formalize loosely structured overlay's main components. This |
185 |
model is based on original Gnutella overlay network with power-law improvements. |
model is based on original Gnutella overlay network with power-law improvements. |
296 |
approach the overlay is constructed determistically, which all participating peers have to follow. The topology of the |
approach the overlay is constructed determistically, which all participating peers have to follow. The topology of the |
297 |
overlay and the placement of services is controlled tightly therefore enabling more scalable and efficient data lookup model. |
overlay and the placement of services is controlled tightly therefore enabling more scalable and efficient data lookup model. |
298 |
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299 |
\subsection{Sketch of a formal definition} |
\subsection{Definition} |
300 |
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301 |
In this subsection, we formalize the main features of tightly structured overlay, i.e., |
In this subsection, we formalize the main features of tightly structured overlay, i.e., |
302 |
identifiers, identifier space and the mapping function. |
identifiers, identifier space and the mapping function. |
350 |
\end{figure} |
\end{figure} |
351 |
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Balakrishnan et al. \cite{balakrishanarticle03lookupp2p} have listed four requirements |
Balakrishnan et al. \cite{balakrishanarticle03lookupp2p} have listed four requirements |
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for tightly structured overlays which have to be addressed in order |
for tightly structured overlays\footnote{Authors use the term 'DHT' in their text, but in this context |
354 |
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it doesn't matter as they list \emph{general} properties of tightly structured overlays.} which have to be addressed in order |
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to perform efficient data lookups in tightly structured overlays. |
to perform efficient data lookups in tightly structured overlays. |
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First, mapping of keys to peers must be done in a load-balanced |
First, mapping of keys to peers must be done in a load-balanced |
357 |
way. Second, the overlay must be able to forward a data lookup for a |
way. Second, the overlay must be able to forward a data lookup for a |
876 |
against the Sybil attack. According to authors, in this technique the IP address of a peer can be verified by the other peer. |
against the Sybil attack. According to authors, in this technique the IP address of a peer can be verified by the other peer. |
877 |
They call this method as a one form of \emph{self-certifying data}. |
They call this method as a one form of \emph{self-certifying data}. |
878 |
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879 |
In the Fail-stop attack model, cited in \cite{naor03simpledht}, a faulty peer is deleted from the Peer-to-Peer system. Thus, |
In the Fail-stop attack model, cited in \cite{naor03simpledht}, a faulty peer is deleted from the Peer-to-Peer system. Thus, |
880 |
a specific data item can be lost from the system temporaraly (or permanently). The reason for the faultiness of a peer can be a |
a specific data item can be lost from the system temporaraly (or permanently). The reason for the faultiness of a peer can be a |
881 |
software failure or a hostile attack. The Byzantine attack model \cite{357176} is closely related to Fail-stop model. The Byzantine model can |
software failure or a hostile attack. The Byzantine attack model \cite{357176} is closely related to Fail-stop model. The Byzantine model can |