820 |
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821 |
\chapter{Open Problems in Peer-to-Peer} |
\chapter{Open Problems in Peer-to-Peer} |
822 |
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823 |
In this chapter, we discuss open problems in Peer-to-Peer research. We describe |
In this chapter, we discuss open problems in Peer-to-Peer research. |
824 |
the open problems and their proposed solutions. Then, we list all issues in |
Note that the open problems list considered here is not meant |
|
tables. Note that the open problems list considered here is not meant |
|
825 |
to be an exhaustive survey of \emph{all} open problems in Peer-to-Peer domain; |
to be an exhaustive survey of \emph{all} open problems in Peer-to-Peer domain; |
826 |
we focus our attention to security, scalability, usability and performance issues |
we focus our attention to some security, scalability, usability and performance related |
827 |
only. |
issues only. |
828 |
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829 |
\section{Overview} |
\section{Overview} |
830 |
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831 |
Partly due to the non-maturity of modern Peer-to-Peer technology, there are several |
Partly due to the non-maturity of modern Peer-to-Peer technology, there are several |
832 |
open problems to be solved. The most severe problems are related to performance, scalability, usability |
open problems to be solved. Also, many techniques developed for traditional distributed |
833 |
and security. Also, many techniques developed for traditional distributed |
systems may no longer apply with Peer-to-Peer systems, e.g., load balancing techiques \cite{byers03dhtbalancing}. |
834 |
systems may no longer apply with Peer-to-Peer systems. Therefore, new solutions are |
|
835 |
needed to make Peer-to-Peer systems more secure and efficient. |
Different problem apply to both the loosely structured and the tightly structured approach have their own specific problems. |
836 |
|
Since the introduction of Gnutella \cite{gnutellaurl}, the main concern has been the scalability problem of loosely structured |
837 |
Both the loosely structured and the tightly structured approach have their own specific problems. |
systems. However, the scalability problem of the loosely structured is often misunderstood; |
838 |
Since Gnutella \cite{gnutellaurl} was first introduced |
\emph{the network overlay} of loosely structured systems is scalable, but the \emph{data lookup model} is not as |
839 |
to the public, researchers' main concern has been the scalability problem of loosely structured |
the data lookup process creates lot of extra network traffic (e.g., \cite{yang02improvingsearch}). |
840 |
systems. However, people often misunderstand the scalability problem of the loosely structured |
|
841 |
approach; \emph{the network overlay} of loosely structured systems is scalable, but the \emph{data lookup model} is not. |
In tightly structured system the main concern is to make overlay's data lookup process |
|
The main concern of the tightly structured system is to make overlay's data lookup process |
|
842 |
more fault tolerant against hostile attacks. Other key problems in tightly structured |
more fault tolerant against hostile attacks. Other key problems in tightly structured |
843 |
systems are the lack of keyword searches, support for heterogeneous peers and load balancing |
systems are the lack of keyword searches, support for heterogeneous peers and load balancing |
844 |
\cite{balakrishanarticle03lookupp2p}. |
\cite{balakrishanarticle03lookupp2p}. |
859 |
currently there are no realizable techniques for this task. Partial solutions for the Sybil attack is to replicate |
currently there are no realizable techniques for this task. Partial solutions for the Sybil attack is to replicate |
860 |
and fragment data items randomly among several participating peers. However, this suggestion assumes that two different |
and fragment data items randomly among several participating peers. However, this suggestion assumes that two different |
861 |
remote entities are actually different; Sybil attacks are still possible and therefore would need centralized |
remote entities are actually different; Sybil attacks are still possible and therefore would need centralized |
862 |
authority for reliable authentication. As the author argues in \cite{douceur02sybil}, without centralized authority, |
authority for reliable authentication. Without centralized authority, |
863 |
Sybil attacks are always possible in a Peer-to-Peer system except under extreme and unrealistic assumptions of |
Sybil attacks are always possible in a Peer-to-Peer system except under extreme and unrealistic assumptions of |
864 |
resource parity and coordination among entities. |
resource parity and coordination among entities \cite{douceur02sybil}. |
865 |
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866 |
In the Fail-stop attack model, cited in \cite{naor03simpledht}, a faulty peer is deleted from the Peer-to-Peer system. |
In the Fail-stop attack model, cited in \cite{naor03simpledht}, a faulty peer is deleted from the Peer-to-Peer system. |
867 |
The reason for the faultiness of a peer can be a software failure or a hostile attack. |
The reason for the faultiness of a peer can be a software failure or a hostile attack. |