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\large{\bf ABSTRACT} \par    
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{\bf Title of Thesis:}\\
Design and Analysis of a Spatially Aware Peer-to-Peer System. \\ 
{\bf Author:} Prashant Punjabi, Master of Science, 2003 \\
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{\bf Thesis directed by:}{\hspace{2.5mm}} Dr. Konstantinos Kalpakis, Associate Professor \\
{\hspace{1.7in}}Deptartment of Computer Science and \\
{\hspace{1.7in}}Electrical Engineering \\
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\begin{abstract}

Peer-to-peer systems (P2P) are proving to be a very popular paradigm. They are seen as obvious replacements to client server technologies, especially in implementations of large scale distributed storage systems. Distributed Hash Tables have emerged as an effective mechanism to implement such systems. There are several protocols to implement a peer-to-peer system as a distributed hash table, but none of these protocols in their basic forms take the physical location of the node in the network into account, while routing a request. This is because the links between nodes of such a system are completely \textit{virtual}, and there is no relation between a direct link between two nodes and their spatial proximity. 
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We propose a scheme in which the arrangement of the nodes and their connections in the P2P system is a direct result of their locations in space. The obvious reasoning behind this is that such an arrangement should considerably reduce the total distance traveled by a message in the system, given the total number of\newpage
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hops taken by a message to reach its destination does not change with this new arrangement. This is because if two connected nodes are close spatially, each hop of a message will have to travel a lesser distance as compared to the possible distance it would have to cover otherwise. The scheme we propose is using Chord as a base protocol and we suggest changes to make the system spatially aware.
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The changes are in the form of an additional logical ring - where the nodes are arranged based on their physical locations. Each node in the system is now part of two rings. The spatial ring is intended to be used as a \textit{cache} to accelerate access to popular documents. The plain ring is used whenever a requested document is not found on the spatial ring. Proactive load balancing is used to ensure that no one node in the system gets overloaded with too many requests.
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We then go on to thoroughly analyze our scheme using experiments based on simulations. We address some of the issues that may arise because of the changes we describe. We provide detailed experimental results demonstrating that our system can offer significant improvements in system performance, when compared with systems that do not incorporate spatial information and are completely virtual. All of the above is achieved without introducing unnecessary load in the system.
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%\footnotetext{Supported in part by NASA under Cooperative Agreement 
%NCC5--315 and Contract NAS5-32337.}

%\addtocounter{footnote}{1}
%\footnotetext{Computer Science and Electrical Engineering Department, 
%University of Maryland Baltimore County, 1000 Hilltop Circle,
%Baltimore, MD 21250.  E-mail:
%pras1@csee.umbc.edu Phone: 410-455-8945
%\{kalpakis,dasgupta,pras1\}@csee.umbc.edu.  Phone: 410-455-3143. Fax:
%410-455-3969.
%\bf Please send all correspondence to Prof. Kalpakis.
%}
