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revision 1.172 by hemppah, Fri Mar 21 15:32:46 2003 UTC revision 1.173 by hemppah, Fri Mar 21 16:23:01 2003 UTC
# Line 820  Here, we describe the listed properties Line 820  Here, we describe the listed properties
820    
821  \chapter{Open Problems in Peer-to-Peer}  \chapter{Open Problems in Peer-to-Peer}
822    
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    
829  \section{Overview}  \section{Overview}
830    
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}.
# Line 861  the Sybil attack would be that the syste Line 859  the Sybil attack would be that the syste
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    
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.

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