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revision 1.171 by hemppah, Fri Mar 21 14:57:40 2003 UTC revision 1.172 by hemppah, Fri Mar 21 15:32:46 2003 UTC
# Line 492  overlays, i.e., $O(\log{n})$ space requi Line 492  overlays, i.e., $O(\log{n})$ space requi
492  the system and $O(\log{n})$ data lookup efficiency.  the system and $O(\log{n})$ data lookup efficiency.
493    
494    
495  \section{Summary}  \section{Differences}
   
 In this section we compare the loosely structured approach and the tightly structured approach.  
 We also summarize proposed Peer-to-Peer algorithms and their key properties with regard  
 to performance and scalability aspects.  
   
 \subsection{Differences}  
496    
497  Even though the loosely structured and the tightly structured approach are both Peer-to-Peer schemes, they  Even though the loosely structured and the tightly structured approach are both Peer-to-Peer schemes, they
498  have very little in common. Indeed, the only thing they share is the fact that no other peer is more  have very little in common. Indeed, the only thing they share is the fact that no other peer is more
499  important than any other in the Peer-to-Peer network. Fault tolerance \emph{may}  important than any other in the Peer-to-Peer network. Fault tolerance \emph{may}
500  be an area, in which approaches have similar properties (e.g., no single point of failure).  be an area, in which approaches have similar properties (e.g., no single point of failure) \cite{milojicic02peertopeer}.
501  Fault tolerance properties of both approaches are currently only initial calculations, or  Fault tolerance properties of both approaches are currently only initial calculations, or
502  experimented in simulation environments. In real-life, however, measuring fault tolerance is a much more  experimented in simulation environments. In real-life, however, measuring fault tolerance is a much more
503  challenging task and requires more research to get reliable answers.  challenging task and requires more research to get reliable answers.
504    
505  The most important difference between approaches is performance and scalability properties. Generally  The most important difference between approaches is performance and scalability properties \cite{balakrishanarticle03lookupp2p}.
506  tightly structured systems can perform all internal operations in a poly-logarithmic time\footnote{However, it is unknown  Generally tightly structured systems can perform all internal operations in a poly-logarithmic time
 whether all proposed algorithms can preserve logarithmic properties in real-life applications or not.}  
507  while the performance of loosely structured systems is not always even linear.  while the performance of loosely structured systems is not always even linear.
508  Moreover, loosely structured systems scale to millions of peers, whereas tightly structured systems are able  Moreover, loosely structured systems scale to millions of peers,
509  to cope with billions of concurrent peers \cite{osokine02distnetworks}, \cite{kubiatowicz00oceanstore}.  whereas tightly structured systems are able to cope with billions of concurrent
510    peers \cite{osokine02distnetworks}, \cite{kubiatowicz00oceanstore}. However, it is unknown
511    whether all proposed algorithms can preserve logarithmic efficiency and scalability properties
512    in real-life applications or not; several tightly structured systems
513    assume that participating peers are homogeneous, and the rate of join or leave operation is low \cite{gurmeet03symphony,
514    \cite{libennowell01observations}}.  
515    
516  To end user, the biggest difference between these systems is how data lookups are performed. Loosely  To end user, the biggest difference between these systems is how data lookups are performed. Loosely
517  structured systems provide more rich and user friendly way of searching data than tightly structured systems  structured systems provide more rich and user friendly way of searching data than tightly structured systems
518  as they have a support for keyword searches. Tightly structured  as they have a support for keyword searches. Tightly structured
519  systems support only exact key lookups since each data item is identified by globally unique keys.  systems support only exact key lookups since each data item is identified by globally unique keys.
520    
521  In the end, both systems have open problems and issues. We will discuss these aspects more detail in  Table \ref{table_comparison_approach} lists the key differences between the loosely structured
 chapter 3. Table \ref{table_comparison_approach} lists the key differences between the loosely structured  
522  approach and the tightly structured approach.  approach and the tightly structured approach.
523    
524    
# Line 609  approach and the tightly structured appr Line 606  approach and the tightly structured appr
606    
607    
608    
609  \subsection{Algorithms}  \section{Algorithms}
610    
611  Table \ref{table_Peer-to-Peer_algorithms} lists proposed Peer-to-Peer algorithms  Table \ref{table_Peer-to-Peer_algorithms} lists proposed Peer-to-Peer algorithms
612  and their key properties with regard to performance and scalability. The list  and their key properties with regard to performance and scalability. The list

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