[Gzz-commits] gzz/Documentation/misc/hemppah-progradu mastert...

[Hermanni Hyytiälä]

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Module name:    gzz
Changes by:     Hermanni Hyytiälä <address@hidden>      03/03/04 03:15:54

Modified files:
        Documentation/misc/hemppah-progradu: masterthesis.tex 
                                             progradu.bib 

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        Started performance

CVSWeb URLs:
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Patches:
Index: gzz/Documentation/misc/hemppah-progradu/masterthesis.tex
diff -u gzz/Documentation/misc/hemppah-progradu/masterthesis.tex:1.105 
gzz/Documentation/misc/hemppah-progradu/masterthesis.tex:1.106
--- gzz/Documentation/misc/hemppah-progradu/masterthesis.tex:1.105      Mon Mar 
 3 10:01:47 2003
+++ gzz/Documentation/misc/hemppah-progradu/masterthesis.tex    Tue Mar  4 
03:15:53 2003
@@ -307,41 +307,6 @@
 \label{fig:gnutella_overlay_cluster}
 \end{figure}  
 
-Additionally, there has been other improvements also. In iterative deepening 
-\cite{yang02improvingsearch}, multiple breadt-first searches are initiated
-with successively larger TTL depth limits, until either the query is 
satisfied, 
-or the maximumum depth $D$ has been reached. To perform a data lookup, query
-originator starts a flood with small TTL value. If the search is not succesful,
-the query originator increases the TTL value and performs another flood. This 
-process is repeated until the desired data is found or maximumum depth $D$ 
-has been reached. Expanding ring, proposed by Shenker et al., 
\cite{lv02searchreplication}, 
-is similar to iterative deepening techique. With these techniques, search 
-may not be fast when desired data item requires many consecutive flooding 
rounds.
-
-Directed breadt-first search \cite{yang02improvingsearch} optimizes the 
original 
-breadt-first searche in way that peer selects neighbors with many quality 
results
-may be reached, thereby maintaining the the quality of costs and decreasing 
the amount
-of messages sent to network. Alpine \cite{alpineurl} and NeuroGrid 
\cite{joseph02neurogrid} 
-Peer-to-Peer system use somewhat similar method when performing data lookups.
-
-Local indices \cite{yang02improvingsearch} in one variation of active caching. 
-In this scheme, each peer maintains an index over the data of all nodes within 
-$h$ hops of itself, where $h$ is a system-wide variable, called radius of the
-index\footnote{In normal BFS case, the value of $h$ is 0, as peer only has 
index
-over its local content.}. Mutual index caching architecture, as proposed in 
-\cite{osokine02distnetworks}, is one variation of local indices techique. 
-
-In random walk approach \cite{lv02searchreplication}, peer forwards a query to 
-randomly selected neighbor. The basic random walk approach decreases the
-overhead generated by messages. On the other hand, basic random walk approach
-has poor response time. As suggested in \cite{lv02searchreplication},
-random walk approach can be done more effective by introducing
-multiple ''walkers''. Freenet \cite{clarke00freenet} Peer-to-Peer system uses 
-random walk searches in query lookups. Indeed, Freenet's query resembles
-depth-first traversal and peers' routing tables are dynamically built
-using caching. This is an outcome of Freenet's main design priciples, 
-i.e., anonymity.
-
 Previously presented improvements are only partial solutions. Obviously, more
 research is required to make loosely structured approach's data lookup more
 scalable and effective. 
@@ -1103,7 +1068,8 @@
 addressing peer-anonymity by providing anonymous-like identifiers to peers 
(e.g., tightly structured peer 
 identifiers).
 
-Anonymity is widely used in those Peer-to-Peer system in which data 
publication is performed. These include
+Anonymity is widely used in those Peer-to-Peer system in which data 
publication and non-censorship are important properties
+of the system. These include
 Freenet \cite{clarke00freenet}, Publius \cite{pub00}, Free haven 
\cite{dingledine00free}, Crowds \cite{reiter98crowds},
 Tangler \cite{502002} and upcoming Mnet \cite{mneturl}. Forwarding proxies are 
used in Freenet, Crowds and 
 Free Haven in order to provide various types of anonymity. Tangler and Publius 
uses cryptographic
@@ -1193,220 +1159,134 @@
 to the problems mentioned above.
 
 
-\scriptsize
-\begin{longtable}{|l|l|l|l|}
-
-\hline 
-\multicolumn{1}{|c|}{\textbf{Problem}} & 
-\multicolumn{1}{c|}{\textbf{Problem description}} & 
-\multicolumn{1}{c|}{\textbf{Solutions}} &
-\multicolumn{1}{c|}{\textbf{Comments/Status}}
-\\ \hline 
-\endfirsthead
-
-\multicolumn{4}{c}%
-{{\tablename\ \thetable{} -- continued from previous page}} \\
-\hline \multicolumn{1}{|c|}{\textbf{Problem}} &
-\multicolumn{1}{c|}{\textbf{Problem description}} &
-\multicolumn{1}{c|}{\textbf{Solutions}} &
-\multicolumn{1}{c|}{\textbf{Comments/Status}} 
-\\ \hline 
-\endhead
-
-\endfoot
-
-
-
-\parbox{90pt}{Query routing \cite{sit02securitycons}, 
\cite{aspnes02faultrouting}, \cite{castro02securerouting}, 
\cite{ratnasamy02routing}, \cite{gavoille01routing}, 
\cite{lynch02atomicdataaccess}} &                        
-\parbox{110pt}{Incorrect forwarding (hostile), incorrect routing (hostile)} &
-\parbox{110pt}{Query monitoring, cross check routing tables, verify routing 
tables, create routing table invariants} &
-\parbox{110pt}{Increases system complexity} 
-\\ \hline
-
-
-\parbox{90pt}{DoS attack \cite{sit02securitycons}, 
\cite{saia02dynamicfaultcontentnetwork}, \cite{datar02butterflies}, 
\cite{daswani02queryflooddos}, \cite{juels99clientpuzzles}} &
-\parbox{110pt}{Distributed, controlled burden againts specific computer(s)} &
-\parbox{110pt}{Client puzzles, load balancing, traffic measurements, traffic 
models, replication} &
-\parbox{110pt}{Only partial solutions, traffic models most effective}
-\\ \hline 
-
-
-\parbox{90pt}{Sybil attack \cite{douceur02sybil}, 
\cite{castro02securerouting}} &
-\parbox{110pt}{Single hostile entity present multiple entities} &
-\parbox{110pt}{Identify all nodes simultaneously across the system, collect 
pool of nodes which are validated, distributed node ID creation} &
-\parbox{110pt}{Not practically realizable, research focused on persistence, 
not on identity distinction}
-\\ \hline 
-
-
-\parbox{90pt}{Spam attack \cite{naor03simpledht}} &
-\parbox{110pt}{Hostile entity creates false versions of data} &
-\parbox{110pt}{Do not trust to single entity, get information from multiple 
entities, trust on majority's opinion} &
-\parbox{110pt}{Easy to implement, creates more network traffic} 
-\\ \hline
-
-
-\parbox{90pt}{Resource spoofing} &
-\parbox{110pt}{Hostile entity gives wrong information about the data which 
entity is responsible for/knows about} &
-\parbox{110pt}{Do not trust to single entity, get information from multiple 
entities, trust on majority's opinion} &
-\parbox{110pt}{Easy to implement, creates more network traffic} 
-\\ \hline
+\section{Performance and usability problems in Peer-to-Peer}
 
+In this section we review open problems regarding performance and usability.
 
-\parbox{90pt}{Entity identification \cite{ajmani02conchord}} &
-\parbox{110pt}{Identify participating entities reliably and efficiently        
} &
-\parbox{110pt}{Digital signatures, key infrastructure} &
-\parbox{110pt}{Not practically realizable}
-\\ \hline
-
+1) Which one is more important: short path length or overhead associated with 
keeping routing tables updated, e.g. number of state updates whenever 
join/leave occurs
+ (number of neighbors)
+2) Are we able to achieve reasonably pathlenghts with less neigbors (Viceroy) ?
+3) How big is the difference between optimal path length and worst case path 
length ?
+4) How difficult is to recover from total routing mislead and the cost of it ?
+5) Can we choose better neighbors by using network latencies instead of 
closeness of IDs in the ID space ? What are the effects doing so ?
+6) Can we choose IDs (globally) based on the geographical location/distance ? 
Is there a working model for doing so ?
+7) How do we should work with node heterogeneity; how big changes have to be 
made to existing algorithms for better support to heterogeneity ?
 
-\parbox{90pt}{Data integrity/authenticity \cite{dabek01widearea}} &
-\parbox{110pt}{Integrity/originality of data is unknown} &
-\parbox{110pt}{Cryptographic content hashes, key architectures} &
-\parbox{110pt}{For data integrity, there are working solutions, but for data 
authenticity, some of the solutions are partial, which may be practically 
realizable}
-\\ \hline
+Principles on scalable search in decentralized, and unstructured networks 
\cite{lv02searchreplication}:
+1) system must support adaptive termination 
+2) message duplication should be minimized
+3) each additional step during search should not significantly increase the 
number of nodes visited
 
+Network proximity: 
+-\cite{pias03lighthouse}, \cite{ng02predicting}
 
-\parbox{90pt}{Anonymity \cite{reiter98crowds}, \cite{tarzan:ccs9}, 
\cite{pub00}, \cite{clarke00freenet}, \cite{reiter98crowds}, 
\cite{352607},\cite{502002}} &
-\parbox{110pt}{Anonymity cannot be provided in all cases} &
-\parbox{110pt}{Remailers, pre-routing} &
-\parbox{110pt}{Total anonymity cannot be provided yet}
-\\ \hline
 
 
-\parbox{90pt}{Malicious nodes \cite{sit02securitycons}, 
\cite{castro02securerouting}} &
-\parbox{110pt}{How to identify malicious nodes in the system} &
-\parbox{110pt}{Create invariants for node behaviour, verify invariants, 
self-certifying data} &
-\parbox{110pt}{Partial solutions, self-certifying data most realiable}
-\\ \hline
+\subsection{Efficient data lookup}
 
+The most intensive research in Peer-to-Peer domain has been focused on 
efficient data lookup methods,
+especially with loosely structured approach. In addition to ''super-peer'' 
method presented in chapter
+2, there has been other improvements also. 
+In iterative deepening 
+\cite{yang02improvingsearch}, multiple breadt-first searches are initiated
+with successively larger TTL depth limits, until either the query is 
satisfied, 
+or the maximumum depth $D$ has been reached. To perform a data lookup, query
+originator starts a flood with small TTL value. If the search is not succesful,
+the query originator increases the TTL value and performs another flood. This 
+process is repeated until the desired data is found or maximumum depth $D$ 
+has been reached. Expanding ring, proposed by Shenker et al., 
\cite{lv02searchreplication}, 
+is similar to iterative deepening techique. With these techniques, search 
+may not be fast when desired data item requires many consecutive flooding 
rounds.
 
-\parbox{90pt}{Access Control \cite{nejdl03accesscontrol}, 
\cite{daswani03openproblems}} &
-\parbox{110pt}{Can we define access control levels in Peer-to-Peer network ?} &
-\parbox{110pt}{Schema-based rules} &
-\parbox{110pt}{Some initial experiences, need more research}
-\\ \hline
+Directed breadt-first search \cite{yang02improvingsearch} optimizes the 
original 
+breadt-first search in way that peer selects neighbors with many quality 
results
+may be reached, thereby maintaining the the quality of costs and decreasing 
the amount
+of messages sent to network. Alpine \cite{alpineurl} and NeuroGrid 
\cite{joseph02neurogrid} 
+Peer-to-Peer system use somewhat similar method when performing data lookups.
 
+Local indices \cite{yang02improvingsearch} in one variation of active caching. 
+In this scheme, each peer maintains an index over the data of all nodes within 
+$h$ hops of itself, where $h$ is a system-wide variable, called radius of the
+index\footnote{In normal BFS case, the value of $h$ is 0, as peer only has 
index
+over its local content.}. Mutual index caching architecture, as proposed in 
+\cite{osokine02distnetworks}, is one variation of local indices techique. 
 
-\parbox{90pt}{Inconsistent behaviour \cite{sit02securitycons}} &
-\parbox{110pt}{Hostile node could act correctly with its neighbors, but 
incorrectly with others} &
-\parbox{110pt}{Public keys, digital signatures} &
-\parbox{110pt}{Not practical approach/working proposal created yet}
-\\ \hline
+In random walk approach \cite{lv02searchreplication}, peer forwards a query to 
+randomly selected neighbor. The basic random walk approach decreases the
+overhead generated by messages. On the other hand, basic random walk approach
+has poor response time. As suggested in \cite{lv02searchreplication},
+random walk approach can be done more effective by introducing
+multiple ''walkers''. Freenet \cite{clarke00freenet} Peer-to-Peer system uses 
+random walk searches in query lookups. Indeed, Freenet's query resembles
+depth-first traversal and peers' routing tables are dynamically built
+using caching. This is an outcome of Freenet's main design priciples, 
+i.e., anonymity.
 
+Since tightly structured systems have efficient data lookup at the application 
level overlay,
+current research efforts are focused on proximity based data lookup. In 
proximity based data lookup,
+peers try to choose routing-tables refering to other peers that are 
\emph{nearby} in
+the underlying network. In this way, tightly structured systems are able to
+decrease actual lookup \emph{latency}. CAN, Kademlia, Pastry and Tapestry have 
a advanced
+heuristics for proximity based routing. Additionally, most recent version of 
Chord uses
+proximity based routing inspired by Karger and Ruhl 
\cite{karger02findingnearest}. Skipnet
+\cite{harvey03skipnet1} uses combination of proximity and application level 
overlay routing 
+when performing data lookups. Authors call this feature \emph{constrained load 
balancing}.
+
+Research related to proximity based routing include 
\cite{karger02findingnearest}, 
+\cite{hildrum02distributedobject}, \cite{brinkmann02compactplacement}, 
\cite{rhea02probabilistic},
+\cite{castro02networkproximity}, \cite{ng02predicting} and 
\cite{pias03lighthouse}. However,
+more research is required to make latency heuristic more effective and 
practical.
 
-\parbox{90pt}{Hostile groups \cite{castro02securerouting}} &
-\parbox{110pt}{Joining node may join parallel network, formed a group of 
hostile nodes, hostile node(s) controls the construction of the network} &
-\parbox{110pt}{Use trusted nodes, based on history information, Cryptography, 
key infrastructure} &
-\parbox{110pt}{Not 100\% sure if Centreal Authority (CA) is missing, not 
practical approach/working proposal created yet}
-\\ \hline
 
+\cite{ripeanu02mappinggnutella}
 
-\parbox{90pt}{External security threats} &
-\parbox{110pt}{Viruses, trojans, sniffers} &
-\parbox{110pt}{Data integrity/authenticity, distributed antivirus software} &
-\parbox{110pt}{Not much research has been done on this}
-\\ \hline
 
-\caption{Security problems in Peer-to-Peer.} 
-\label{table_security_problems_Peer-to-Peer}
 
 
-\end{longtable}
-\normalsize
-       
 
 
 
 
-Censorship \cite{502002}
 
-\cite{douceur02sybil}
+\cite{crespo02semanticoverlay}
+Locality \cite{keleher-02-p2p}
 
 
 
+\subsection{Fast and usable search}
 
-\section{Performance and usability problems in Peer-to-Peer}
+To make Peer-to-Peer systems usable in a large, these systems have to support 
flexible, efficient
+and easy to use search methods. For instance, Internet's perhaps the most 
important feature
+is the ability to perform keyword or fuzzy searches (e.g., Google). Currently, 
only loosely
+structured systems are able carry out this requirement. Unfortunately, as 
discussed in this text,
+the data loouk model of loosely structured approach is not scalable. Thus, 
research efforts have
+been focused on tightly structured approach. 
+The main in problem with tightly structured approach is the fact that tightly 
structured algorihms
+performs data lookups based on a unique identifier. However, quite recently 
have been studies
+on the feasibility of Peer-to-Peer Web-like indexing and searching 
\cite{li03feasibility}. Authors
+argue, that it is possible to implement Peer-to-Peer Web-like search with 
certain radical compromises. 
+First, Peer-to-Peer search enginge may need to decrease result quality in 
order make searching more
+efficient. Second, Peer-to-Peer systems must observe better the properties of 
underlying network for
+better performance. Study list include \cite{kronfol02fasdsearch}, 
\cite{harren02complex}, 
+\cite{joseph02p2players}, \cite{Bhattacharjee03resultcache}, 
\cite{andrzejak02rangequeries},
+\cite{ansaryefficientbroadcast03} and \cite{chord:om_p-meng}. 
+
+Many techniques have been developed in order to provide more efficient search 
indexing. First, as 
+studies queries follow Zipf-like distributions \cite{breslau98implications} 
caching and precomputation
+can be done for optimizting search indices \cite{li03feasibility}. Second, 
regular compression algorithms
+and Bloom filters \cite{362692} can be used for even better optimizations. 
 
-1) Which one is more important: short path length or overhead associated with 
keeping routing tables updated, e.g. number of state updates whenever 
join/leave occurs
- (number of neighbors)
-2) Are we able to achieve reasonably pathlenghts with less neigbors (Viceroy) ?
-3) How big is the difference between optimal path length and worst case path 
length ?
-4) How difficult is to recover from total routing mislead and the cost of it ?
-5) Can we choose better neighbors by using network latencies instead of 
closeness of IDs in the ID space ? What are the effects doing so ?
-6) Can we choose IDs (globally) based on the geographical location/distance ? 
Is there a working model for doing so ?
-7) How do we should work with node heterogeneity; how big changes have to be 
made to existing algorithms for better support to heterogeneity ?
 
-Principles on scalable search in decentralized, and unstructured networks 
\cite{lv02searchreplication}:
-1) system must support adaptive termination 
-2) message duplication should be minimized
-3) each additional step during search should not significantly increase the 
number of nodes visited
 
-Network proximity: 
--\cite{pias03lighthouse}, \cite{ng02predicting}
 
-Efficient searching:
--result caching and view trees \cite{Bhattacharjee03resultcache} (insight: 
store and and retrieve prior results from view tree)
--bloom filters \cite{362692}
 
 
-\subsection{Efficient data lookup}
 
--Object's popularity: studies have shown that Napster, Gnutella and Web 
-queries follow Zipf-like distributions (1/2, 1/3, 1/4 etc.)
 
 
-Proposals (Yand et all):
 
-Iterative Deepening
-In Iterative Deepening, multiple BFS are initiated with successively larger
-depths limits, until either they query is satisfied, or the maximum depth L
- has been reached
- 
-Directed BFS
-Implements a strategy where a source sends a query messages to just a subset 
-of neighbours and selecting neighbors through which nides with many quality 
results
- may be reached. Node may select a neighbor that has produced or forwarded 
many 
- many quality results in the past, on the premise that past performance is a 
good 
- indication of future performance.
-
-Local Indices
-In this method, each node N maintains an index over the data of all nodes 
within h hops 
-of itself, where h is a system-wide variable known as radius of the index (h=0 
is th  BFS case).
- When a node receives a query message, it can process the query on behalf of 
every node within
- r hops.
-
-
-\cite{ratnasamy02routing}
-\cite{hildrum02distributedobject}
-\cite{adamic02localsearch}
-\cite{adamic01powerlawsearch}
-\cite{ripeanu02mappinggnutella}
-\cite{lv02searchreplication}
-\cite{brinkmann02compactplacement}
-\cite{lv02gnutellascalable}
-\cite{osokine02distnetworks}
-\cite{harvey03skipnet1}
-\cite{rhea02probabilistic}
-\cite{ansaryefficientbroadcast03}
-\cite{castro02networkproximity}
-\cite{yang02efficientsearch}
-\cite{crespo02semanticoverlay}
-Locality \cite{keleher-02-p2p}
-\cite{ng02predicting}
 
-\subsection{Fault-tolerance and robustness}
 
-\subsection{Fast and usable search}
-\cite{yang02improvingsearch}
-\cite{kronfol02fasdsearch}
-\cite{harren02complex}
-\cite{joseph02p2players}
-Bloom filters \cite{362692}
-\cite{andrzejak02rangequeries}
-\cite{li03feasibility}
-\cite{CuencaAcuna2002DSIWorkshop}
-\cite{Bhattacharjee03resultcache}
-\cite{chord:om_p-meng}
 
 \cite{ramanathan02goodpeers}
 
@@ -1550,6 +1430,127 @@
        -solution: need a way to control creation of node IDs (ID = 
SHA-1(ip-address), challange node verify its ID)
 
 
+
+\scriptsize
+\begin{longtable}{|l|l|l|l|}
+
+\hline 
+\multicolumn{1}{|c|}{\textbf{Problem}} & 
+\multicolumn{1}{c|}{\textbf{Problem description}} & 
+\multicolumn{1}{c|}{\textbf{Solutions}} &
+\multicolumn{1}{c|}{\textbf{Comments/Status}}
+\\ \hline 
+\endfirsthead
+
+\multicolumn{4}{c}%
+{{\tablename\ \thetable{} -- continued from previous page}} \\
+\hline \multicolumn{1}{|c|}{\textbf{Problem}} &
+\multicolumn{1}{c|}{\textbf{Problem description}} &
+\multicolumn{1}{c|}{\textbf{Solutions}} &
+\multicolumn{1}{c|}{\textbf{Comments/Status}} 
+\\ \hline 
+\endhead
+
+\endfoot
+
+
+
+\parbox{90pt}{Query routing \cite{sit02securitycons}, 
\cite{aspnes02faultrouting}, \cite{castro02securerouting}, 
\cite{ratnasamy02routing}, \cite{gavoille01routing}, 
\cite{lynch02atomicdataaccess}} &                        
+\parbox{110pt}{Incorrect forwarding (hostile), incorrect routing (hostile)} &
+\parbox{110pt}{Query monitoring, cross check routing tables, verify routing 
tables, create routing table invariants} &
+\parbox{110pt}{Increases system complexity} 
+\\ \hline
+
+
+\parbox{90pt}{DoS attack \cite{sit02securitycons}, 
\cite{saia02dynamicfaultcontentnetwork}, \cite{datar02butterflies}, 
\cite{daswani02queryflooddos}, \cite{juels99clientpuzzles}} &
+\parbox{110pt}{Distributed, controlled burden againts specific computer(s)} &
+\parbox{110pt}{Client puzzles, load balancing, traffic measurements, traffic 
models, replication} &
+\parbox{110pt}{Only partial solutions, traffic models most effective}
+\\ \hline 
+
+
+\parbox{90pt}{Sybil attack \cite{douceur02sybil}, 
\cite{castro02securerouting}} &
+\parbox{110pt}{Single hostile entity present multiple entities} &
+\parbox{110pt}{Identify all nodes simultaneously across the system, collect 
pool of nodes which are validated, distributed node ID creation} &
+\parbox{110pt}{Not practically realizable, research focused on persistence, 
not on identity distinction}
+\\ \hline 
+
+
+\parbox{90pt}{Spam attack \cite{naor03simpledht}} &
+\parbox{110pt}{Hostile entity creates false versions of data} &
+\parbox{110pt}{Do not trust to single entity, get information from multiple 
entities, trust on majority's opinion} &
+\parbox{110pt}{Easy to implement, creates more network traffic} 
+\\ \hline
+
+
+\parbox{90pt}{Resource spoofing} &
+\parbox{110pt}{Hostile entity gives wrong information about the data which 
entity is responsible for/knows about} &
+\parbox{110pt}{Do not trust to single entity, get information from multiple 
entities, trust on majority's opinion} &
+\parbox{110pt}{Easy to implement, creates more network traffic} 
+\\ \hline
+
+
+\parbox{90pt}{Entity identification \cite{ajmani02conchord}} &
+\parbox{110pt}{Identify participating entities reliably and efficiently        
} &
+\parbox{110pt}{Digital signatures, key infrastructure} &
+\parbox{110pt}{Not practically realizable}
+\\ \hline
+
+
+\parbox{90pt}{Data integrity/authenticity \cite{dabek01widearea}} &
+\parbox{110pt}{Integrity/originality of data is unknown} &
+\parbox{110pt}{Cryptographic content hashes, key architectures} &
+\parbox{110pt}{For data integrity, there are working solutions, but for data 
authenticity, some of the solutions are partial, which may be practically 
realizable}
+\\ \hline
+
+
+\parbox{90pt}{Anonymity \cite{reiter98crowds}, \cite{tarzan:ccs9}, 
\cite{pub00}, \cite{clarke00freenet}, \cite{reiter98crowds}, 
\cite{352607},\cite{502002}} &
+\parbox{110pt}{Anonymity cannot be provided in all cases} &
+\parbox{110pt}{Remailers, pre-routing} &
+\parbox{110pt}{Total anonymity cannot be provided yet}
+\\ \hline
+
+
+\parbox{90pt}{Malicious nodes \cite{sit02securitycons}, 
\cite{castro02securerouting}} &
+\parbox{110pt}{How to identify malicious nodes in the system} &
+\parbox{110pt}{Create invariants for node behaviour, verify invariants, 
self-certifying data} &
+\parbox{110pt}{Partial solutions, self-certifying data most realiable}
+\\ \hline
+
+
+\parbox{90pt}{Access Control \cite{nejdl03accesscontrol}, 
\cite{daswani03openproblems}} &
+\parbox{110pt}{Can we define access control levels in Peer-to-Peer network ?} &
+\parbox{110pt}{Schema-based rules} &
+\parbox{110pt}{Some initial experiences, need more research}
+\\ \hline
+
+
+\parbox{90pt}{Inconsistent behaviour \cite{sit02securitycons}} &
+\parbox{110pt}{Hostile node could act correctly with its neighbors, but 
incorrectly with others} &
+\parbox{110pt}{Public keys, digital signatures} &
+\parbox{110pt}{Not practical approach/working proposal created yet}
+\\ \hline
+
+
+\parbox{90pt}{Hostile groups \cite{castro02securerouting}} &
+\parbox{110pt}{Joining node may join parallel network, formed a group of 
hostile nodes, hostile node(s) controls the construction of the network} &
+\parbox{110pt}{Use trusted nodes, based on history information, Cryptography, 
key infrastructure} &
+\parbox{110pt}{Not 100\% sure if Centreal Authority (CA) is missing, not 
practical approach/working proposal created yet}
+\\ \hline
+
+
+\parbox{90pt}{External security threats} &
+\parbox{110pt}{Viruses, trojans, sniffers} &
+\parbox{110pt}{Data integrity/authenticity, distributed antivirus software} &
+\parbox{110pt}{Not much research has been done on this}
+\\ \hline
+
+\caption{Security problems in Peer-to-Peer.} 
+\label{table_security_problems_Peer-to-Peer}
+
+
+\end{longtable}
+\normalsize
        
                
 
Index: gzz/Documentation/misc/hemppah-progradu/progradu.bib
diff -u gzz/Documentation/misc/hemppah-progradu/progradu.bib:1.92 
gzz/Documentation/misc/hemppah-progradu/progradu.bib:1.93
--- gzz/Documentation/misc/hemppah-progradu/progradu.bib:1.92   Mon Mar  3 
10:01:47 2003
+++ gzz/Documentation/misc/hemppah-progradu/progradu.bib        Tue Mar  4 
03:15:53 2003
@@ -2060,3 +2060,13 @@
        volume = {22},
        year = {1979}
 } 
+
+
+
address@hidden,
+       author = "L. Breslau and P. Cao and L. Fan and G. Phillips and S. 
Shenker",
+       title = "On the Implications of Zipf's Law for Web Caching",
+       booktitle = "In proceedings of the 3rd International WWW Caching 
Workshop",     
+       year = "1998",
+       month = "June",         
+}