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[Hermanni Hyytiälä]

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Index: gzz/Documentation/misc/hemppah-progradu/masterthesis.tex
diff -u gzz/Documentation/misc/hemppah-progradu/masterthesis.tex:1.125 
gzz/Documentation/misc/hemppah-progradu/masterthesis.tex:1.126
--- gzz/Documentation/misc/hemppah-progradu/masterthesis.tex:1.125      Thu Mar 
 6 10:12:32 2003
+++ gzz/Documentation/misc/hemppah-progradu/masterthesis.tex    Fri Mar  7 
03:53:41 2003
@@ -19,7 +19,7 @@
 %***********************
 \title{Fenfire in Peer-to-Peer Environment}
 
-\translatedtitle{Fenfire vertaisverkko ympäristössä}
+\translatedtitle{Fenfire ja vertaisverkot}
 
 \author{Hermanni Hyytiälä}
 
@@ -45,13 +45,13 @@
 problems, which have not solutions at all, or problems have proposed
 solutions but they are practically unrealizable.
 
-Then, we give an overview of our Fenfire system.  We evaluate existing
+Then, we give an overview of Fenfire system.  We evaluate existing
 Peer-to-Peer approaches-- loosely and tightly structured overlays-- with regard
 to Fenfire's needs. Finally, we propose simple algorithms to efficiently find 
Fenfire
 related data from Peer-to-Peer network.
 }
 \tiivistelma{
-Tässä opinnäytetyössä arvioimme olemassaolevia vertaisverkkoja, protokollia ja
+Tässä opinnäytetyössä arvioimme olemassaolevia vertaisverkkoja, algoritmeja ja
 niiden erityisominaisuuksia. Teemme yhteenvedon olemassa olevista ongelmista
 vertaisverkoissa ja jaamme ongelmat kolmeen alakategoriaan. Havaitsemme, että
 on olemassa useita ongelmia, joihin ei ole ratkaisua lainkaan, tai on ehdotelma
@@ -87,8 +87,8 @@
 and reliability againts certain kinds of faults (e.g., single point of 
failure).
 
 There are many definitions of Peer-to-Peer networks. The Intel Peer-to-Peer 
-Working Group defines it as ''the sharing of computer resources and defines
-and services by direct exchange between systems'' \cite{p2pworkinggroup}. 
+Working Group defines it as ''the sharing of computer resources and services 
+by direct exchange between systems'' \cite{p2pworkinggroup}. 
 Dave Winer \cite{winer00whatisp2p} lists several
 properties of Peer-to-Peer network, while most notably the statement 
 ''The user's machine is a client and a server'' describes best Peer-to-Peer
@@ -106,14 +106,14 @@
 Specifically, we review existing Peer-to-Peer approaches, algorithms and their 
key properties. We observe
 that despite of greate amount of proposed Peer-to-Peer systems, all systems 
fall either
 loosely structured approach or tightly structured approach. We also discuss 
open problems in 
-Peer-to-Peer networks and divide problems into three sub-categories: security 
related problems, 
+Peer-to-Peer systems and divide problems into three sub-categories: security 
related problems, 
 performance related problems and miscellaneous problems. In the end, we 
summarize all 
 problems in easy-to-understand tables. 
 
-Next, we give an overview of our Fenfire hypermedia system, which implements 
xanalogical storage model. We
+Next, we give an overview of Fenfire hypermedia system, which implements 
xanalogical storage model. We
 also describe briefly Storm software module of Fenfire system, which is an 
essential part of Fenfire's
 Peer-to-Peer functionality. We evaluate existing Peer-to-Peer approaches and
-choose the best alternative to our needs. We discover that Fenfire, 
xanalogical model and
+choose the best alternative to Fenfire's needs. We discover that Fenfire, 
xanalogical model and
 tightly structured Peer-to-Peer approach all have similar method to deal with 
data,
 i.e., globally unique identifiers. Finally, we propose system model for 
Fenfire in Peer-to-Peer
 environment and present yet simple but efficient algortihms to be used for 
data lookups in 
@@ -140,8 +140,8 @@
 address open problems in Peer-to-Peer domain and divide problems into three
 sub-categories. Chapter 4 gives an overview of Fenfire system. In chapter
 5, we evaluate existing Peer-to-Peer approaches with regard to Fenfire system, 
propose system
-model for Fenfire in Peer-to-Peer environment, present simple algorithms to 
perform data 
-lookups in Peer-to-Peer environment. Also, we discuss possible problems of 
using Fenfire
+model for Fenfire in Peer-to-Peer environment and present simple algorithms to 
perform data 
+lookups in Peer-to-Peer environment. In addition, we discuss possible problems 
of using Fenfire
 in Peer-to-Peer environment. In chapter 6, we present conclusions and future 
work.
 
 
@@ -178,7 +178,7 @@
 \label{fig:application_level}
 \end{figure}
 
-Compared to ARPANET's Peer-to-Peer functionality, today's Peer-to-Peer systems
+Compared to ARPANET's Peer-to-Peer functionality, modern Peer-to-Peer systems
 are ad-hoc, i.e., peers join and leave the system constantly in a dynamic 
manner. This
 fact constitutes challenging requirements for efficient construction and 
maintenance
 of the overlay network. Even more demanding tasks are how to perform efficient 
data
@@ -192,7 +192,7 @@
 other research areas than computer science. There has been done research 
regarding 
 to ad-hoc nature of complex networks \cite{albert-02-statistical}, 
\cite{albert-00-tolerance}, \cite{watts00dynamics}. 
 It's interesting to realize that chemical properties of cells, the Internet, 
ad-hoc 
-Peer-to-Peer networks, have all in common that they self-organize based on 
same 
+Peer-to-Peer systems, have all in common that they self-organize based on same 
 principles.  Furthermore, the assocation between social connections among 
people 
 and Peer-to-Peer overlay topology has been studied recently  
\cite{watts00dynamics}, 
 \cite{kleinberg99small}, \cite{nips02-Kleinberg}. This insight is motivated
@@ -226,7 +226,7 @@
 
 \section{Loosely structured}
 
-Gnutella \cite{gnutellaurl} is well-known example of loosely structured 
overlay network. As in
+Gnutella \cite{gnutellaurl} is a well-known example of loosely structured 
overlay network. As in
 other Peer-to-Peer networks, no peer is more important than any other peer in 
the network.
 The construction and maintenance of Gnutella network is extremely ad-hoc, 
since participating
 peers can form the overlay network based on \emph{local} knowledge. Figure 
\ref{fig:gnutella_overlay}
@@ -318,7 +318,7 @@
 all peers $p$ in system. Then, $\forall s \in S$, there is a provider of the 
service, 
 expressed as $p = provider(s)$. Every $p$ has neighbor(s), named as 
$neighbor$, which 
 is $P$ = \{$p \in P: \exists neighbor$, which is randomly chosen from $P$\}.
-Super peer is a peer, which hosts the indices of other peers, $sp = 
summaryindex(provider(s))$.
+\emph{Super peer} is a peer, which hosts the indices of other peers, $sp = 
summaryindex(provider(s))$.
 Moreover, $\forall$ reqular peer $p$, there is super peer, which has has a 
index of regular
 peer's content, specifically $ps$, $P$ = \{$p \in P: \exists ps$, 
 where $ps$ = $summaryindex(provider(s)) \wedge (p = provider(s))$\}
@@ -345,19 +345,10 @@
 space differs between proposed systems. Circular identifier space (and 
variants) 
 is most widely used. For instance, Chord \cite{stoica01chord}, Koorde 
\cite{kaashoek03koorde}, 
 Pastry \cite{rowston01pastry}, SWAN \cite{bonsma02swan}, Tapestry 
\cite{zhao01tapestry}
-and Viceroy \cite{malkhi02viceroy} use a circular identifier space of $n$-bit 
integers modulo $2^{n}$. The
+and Viceroy \cite{malkhi02viceroy} use circular identifier space of $n$-bit 
integers modulo $2^{n}$. The
 value of $n$ varies among systems. Again, CAN \cite{ratnasamy01can} uses a 
$d$-dimensional cartesian 
 model to implement identifier space.
 
-Stoica et al.. \cite{balakrishanarticle03lookupp2p} have listed 
-four requirements for tightly structured overlays, which have to be 
-addressed in order to perform data lookups in tightly structured overlays. 
-First, mapping of keys to peers must be done in a load-balanced
-way. Second, the overlay must be able to forward a lookup for a 
-specific key to an approriate peer. Third, overlay must have a
-support for a distance function. Finally,  routing tables for each peer
-must be constructed and maintained adaptively.
-
 To store data into tightly structured overlay, each application-specific
 unique key (e.g., SHA-1 \cite{fips-sha-1}) is \emph{mapped} uniformly (e.g., 
using consistent
 hashing \cite{258660}) by the overlay to a existing peer in the overlay. Thus, 
tightly 
@@ -411,6 +402,15 @@
 for maintaining information about other peers in the system and 
 $O(\log{n})$ data lookup efficiency.
 
+Stoica et al. \cite{balakrishanarticle03lookupp2p} have listed 
+four requirements for tightly structured overlays, which have to be 
+addressed in order to perform efficient data lookups in tightly structured 
overlays. 
+First, mapping of keys to peers must be done in a load-balanced
+way. Second, the overlay must be able to forward a lookup for a 
+specific key to an approriate peer. Third, overlay must have a
+support for a distance function. Finally,  routing tables for each peer
+must be constructed and maintained adaptively.
+
 Currently, all proposed tightly structured overlays provide at least 
 poly--logaritmical data lookup operations. However, there are some key 
 differences in the data structure that they use as a routing table. For 
example, Chord 
@@ -502,8 +502,7 @@
 function is defined as $map: I \longmapsto IS$, and coordinate point as 
 $ip = map(identifier(s))$, which maps data items, expressed by a identifier to 
coordinate 
 point $ip$ in $(IS,d)$. Peer's p resources are mapped onto a set $IS$ = \{$ip 
\in IS: 
-\exists s \in S$, $ip = map(identifier(s)) \wedge (provider(s) = p)$\}., 
-which means that resources which peer provides into the system are not kept 
locally.
+\exists s \in S$, $ip = map(identifier(s)) \wedge (provider(s) = p)$\}.
 Every $p$ has neighbor(s), named as $neighbor$, which are $P$ = \{$p \in P: 
\exists neighbor$, 
 where $difference(p,p_neighbor)= ''close''$, where $''close''$ is small 
difference $d$ in $(IS,d)$\}.
 
@@ -650,11 +649,11 @@
 
 Table \ref{table_Peer-to-Peer_algorithms} lists proposed Peer-to-Peer 
algorithms 
 and their key properties with regard to performance and scalability. List 
-includes algorithms from two main approaches. However, majority of the 
algorithms 
+includes algorithms from both loosely and tightly structured approaches. 
However, majority of the algorithms 
 listed above belongs to tightly structured approach since there has been 
active 
 research being pursued towards tightly structured approach lately. List 
doesn't 
 include \emph{all} proposed Peer-to-Peer algorithms. Only the ones which 
already have 
-been widely deployed in real-life, or the ones which may promising in the 
future's 
+been widely deployed in real life, or the ones which may promising in the 
future's 
 Peer-to-Peer systems are included in this thesis.
  
 We decided to follow the guidelines from \cite{kaashoek03koorde} when
@@ -663,13 +662,13 @@
 in face of real life requirements. Additionally, however, we decided to include
 the number of \emph{real} network connections for each peer in the overlay. 
 
-Here, we describe the listed properties of Peer-to-Peer algorihms:
+Here, we describe the listed properties of Peer-to-Peer algorithms:
 
 \begin{itemize}
-\item \textbf{Lookup}: Number of messages required when a data lookup is 
performed
-\item \textbf{Space}: Number of neighbors which peers knows about (neighbors) 
-\item \textbf{Insert/delete}: Number of messages required when a peer joins or 
leaves the network
- \item \textbf{Number of network connections}: Number of concurrent network 
connections required to maintain correct neighbor information
+\item \textbf{Lookup}: number of messages required when a data lookup is 
performed
+\item \textbf{Space}: number of neighbors which peers knows about (neighbors) 
+\item \textbf{Insert/delete}: number of messages required when a peer joins or 
leaves the network
+ \item \textbf{Number of network connections}: number of concurrent network 
connections required to maintain correct neighbor information
 \end{itemize}
 
 \scriptsize
@@ -873,7 +872,7 @@
 \section{Overview}
 
 Partly due to the non-maturity of modern Peer-to-Peer technology, it has 
several
-open problems to be solved. Main open problems are related to performance, 
scalability, usability
+open problems to be solved. The most severe problems are related to 
performance, scalability, usability
 and security. More important, many techniques developed for traditional 
distributed
 systems may no longer apply with Peer-to-Peer systems. Therefore, new 
solutions are 
 needed to make Peer-to-Peer systems more secure and efficient.
@@ -885,12 +884,13 @@
 approach; \emph{network} of loosely structured systems is scalable, but the 
\emph{data lookup model} is not. 
 The main concern of tightly structured system is to make overlay's data lookup 
 routing more flexible againts hostile attacks. Another key problems in tightly 
structured 
-systems are the lack of keyword searches and support for heterogeneous peers.
+systems are the lack of keyword searches, support for heterogeneous peers and 
load balancing
+\cite{balakrishanarticle03lookupp2p}.
 
 To make Peer-to-Peer systems even more popular (e.g., in industry), 
Peer-to-Peer domain
 needs better infrastructures to deal with security issues. There has been done 
some
 research regarding anonymity, access control, data availability and data 
integrity but as
-we will observe, much more research work is required to solve security related 
issues.
+we state in the following sections, much more research work is required to 
solve security related issues.
 
 \section{Security problems in Peer-to-Peer}
 
@@ -905,7 +905,7 @@
 In Sybil attack model, hostile entity presents multiple 
 entities. Therefore, one hostile entity can control a large fraction of the 
Peer-to-Peer system. Optimal
 possible solution to Sybil attack would be that system could \emph{distinct} 
entities of the system reliably. Unfortunately,
-currently there no realizable techiques for this task. Partial solutions for 
Sybil is attack is to replicate
+currently there no realizable techiques for this task. Partial solutions for 
Sybil attack is to replicate
 and fragment data randomly among several participating peer. However, both 
suggestions assume that two different 
 remote entities are actually different; Sybil attacks are still possible and 
therefore, would need centralized 
 authority for reliable authentication. As author arques in 
\cite{douceur02sybil}, without centralized authority, 
@@ -923,13 +923,13 @@
 attack, hostile or faulty peer may produce false information of the data, or 
refuses/is not able to reply to requests. 
 Possible solution againts this attack is that peer should not trust to single 
entity. Instead, peer should get 
 information from multiple entities and trust on majority's opinion. This 
methods requires more messages to be 
-sent to network whilce increasing the load of system. However, if Spam attack 
is combined with Sybil attack, obviously 
+sent to network while increasing the load of system. However, if Spam attack 
is combined with Sybil attack, obviously 
 previously mentioned solution doesn't work. Again, more research is required 
to solve this attack model 
-reliability. Naor et al. \cite{naor03simpledht} has proposed a partial 
solution againts Spam attack with 
+safely. Naor et al. \cite{naor03simpledht} has proposed a partial solution 
againts Spam attack with 
 \emph{faulty} peers (not hostile).
 
 Traditional overload of targeted peers is best known form of distrubuted 
Denial of Service attack (DDoS). For example, 
-hostile entity can attempt to burden targetted peers with garbage packets. As 
a implication, peers may act
+hostile entity can attempt to burden targetted peers with garbage network 
packets. As a implication, peers may act
 incorrectly or stop working. DDoS attack may be very severe, especially if 
rate of replication and caching 
 in Peer-to-Peer system is low. This may lead to data loss in the Peer-to-Peer 
system. Daswani et al. 
 \cite{daswani02queryflooddos} has done research regarding to this subject. 
Authors suggest efficient load balancing 
@@ -950,7 +950,7 @@
 Implementations include Advogato \cite{advogatourl}. None of the current 
proposals or implementations 
 based on reputation address trust in a reliable way.
 
-Optimal solution for trust in Peer-to-Peer systems would be certificate based 
security methods.
+Optimal solution for trust in Peer-to-Peer systems would be certificate based 
security models.
 Quite recently, widely used Public Key Infrastructure (PKI) has been deployed 
in distributed
 systems \cite{rivest96sdsi}, \cite{spkiworkinggroup}. PKI is an reliable 
technology for securing
 data in rather \emph{static} computing systems, such as in the Internet. 
However, in Peer-to-Peer 
@@ -962,7 +962,7 @@
 ConChord \cite{ajmani02conchord} is the first Peer-to-Peer system which has a 
support for PKI based
 security infrastructure. Unfortunately, ConChord is in early in development 
and lacks of important
 features of PKI to be fully usable yet. Furthermore, the hierarchy of 
SDSI/SPKI \cite{rivest96sdsi}, 
-\cite{spkiworkinggroup} may a problem for Peer-to-Peer systems, in which 
hierarchy is intentionally missing.
+\cite{spkiworkinggroup} may be a problem for Peer-to-Peer systems, in which 
hierarchy is intentionally missing.
 
 For data integrity, on the other hand, there are few working solutions. 
Cryptographic content hashes
 \cite{fips-sha-1}, variations \cite{merkle87hashtree} and their implementation 
techniques \cite{mohr02thex},
@@ -978,11 +978,11 @@
 no one is able to link publisher to a specific document. Reader-anonymity 
means that a specific
 document cannot be linked to document's readers. This form of anonymity 
protects the privacy of a
 users of the system. Furthermore, peer-anonymity means that no peer can be 
linked to a specific document, i.e.,
-no one is able to determine the peer, where document was originally published. 
Document-anonymity
+no one is able to determine the peer, in where document was originally 
published. Document-anonymity
 means that peer doesn't know which data it is currently hosting. Finally, 
query-anonymity is a form
 of document-anonymity; when other peers performs data lookups, peer doesn't 
know which data it serves
 to the data lookup originators. As the authors cite, some of forms of 
anonymity may imply each other and
-possible issues are one area of future work.
+possible issues raised by this property is one area of future work.
 
 With regard to anonymity in Peer-to-Peer systems, there has been done much 
research work both at network 
 level layer \cite{tarzan:ccs9} and at application level layer 
\cite{reiter98crowds}, \cite{mixminionurl}.
@@ -1061,10 +1061,10 @@
 maintenance, but their solution seems to have to major problems 
\cite{castro02securitystructured}. First,
 the solution is very expensive even without faulty or hostile entities. 
Second, each group of replicas
 in their solution must have less than 1/3 of its peer faulty. Thus, this 
feature results in a low
-probability of succesfull routing.
+probability of succesful routing.
 
-Aspnes et al. in \cite{aspnes02faultrouting} and Kaashoek et al.l in 
\cite{kaashoek03koorde} formally 
-prove the lower and upper bounds for space requirements of locating a specific 
date item in 
+Aspnes et al. in \cite{aspnes02faultrouting} and Kaashoek et al. in 
\cite{kaashoek03koorde} formally 
+prove the lower and upper bounds for space requirements of locating a specific 
data item in 
 Peer-to-Peer system. They show that to provide high degree of fault tolerance 
and efficiency, each 
 participating peer must maintain average of $O(\log{n})$ neighbors. 
 
@@ -1081,10 +1081,10 @@
 
 \subsection{Other security threats}
 
-Ross Lee graham lists several external threats againts Peer-to-Peer networks 
\cite{grahamp2psecurity}. Most important, t
-he list includes viruses and trojans. Currently, there are not even partial 
solutions
+Ross Lee graham lists several external threats againts Peer-to-Peer networks 
\cite{grahamp2psecurity}. Most important, 
+the list includes viruses and trojans. Currently, there are not even partial 
solutions
 to the problems mentioned above. General robustness properties of Peer-to-Peer 
system is able to 
-deal with software failures and hostile attack, but redundancy againts 
external threats is unknown. 
+deal with software failures and hostile attack, but fault tolerance againts 
external threats is unknown. 
 The reason for this is that there are no experiences on these kinds of 
attacks. Possible solution 
 would be distributed anti-virus software, but much more intensive research is 
required until
 this kind of solution would be applicable. 
@@ -1108,7 +1108,7 @@
 originator starts a data lookup with small TTL value. If the search is not 
succesful,
 the query originator increases the TTL value and performs another data lookup. 
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}, 
+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.
 
@@ -1125,7 +1125,7 @@
 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 
+In random walk approach \cite{lv02searchreplication}, peer forwards 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},
@@ -1134,7 +1134,8 @@
 random walk searches in query lookups. Indeed, Freenet's query resembles
 Depth-First-Search (DFS) and peers' routing tables are dynamically built
 using caching. This is an outcome of Freenet's main design priciples, 
-i.e., anonymity. Additional improvements to Freenet's data lookup using
+i.e., anonymity. Another property of Freenet's data lookup model is that
+it adapts well with varying usage patterns. Improvements to Freenet's data 
lookup using
 ''small-world phenomenon'' has been proposed by Zhang et al.. 
\cite{zhang02using}.
 
 
@@ -1165,8 +1166,8 @@
 been focused on tightly structured approach. 
 The main problem with tightly structured approach is the fact that tightly 
structured algorihms
 performs data lookups based on a globally unique identifier (key). Quite 
recent study has been focused 
-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. 
+on the feasibility of Peer-to-Peer Web-like indexing and searching 
\cite{li03feasibility} on top of
+tightly structured overlays. Authors argue, that it is possible to implement 
Peer-to-Peer Web-like search with certain radical compromises. 
 First, Peer-to-Peer search engine 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. 
@@ -1182,8 +1183,8 @@
 distributions\footnote{Zipf distribution is a variant of power-law function. 
 Zipf-distribution can be used in observation of frequency of occurrence event 
$E$, as a function of the rank 
 $i$ when the rank is determined by the frequency of occurrence, $E_i \sim 
\frac{1}{i^{a}}$, where the exponent 
-$a$ is close to unity.} (e.g., \cite{breslau98implications}), caching and 
precomputation
-can be done for optimizting search indices \cite{li03feasibility}. Regular 
compression algorithms,
+$a$ is close to unity.} (e.g., \cite{breslau98implications}). Therefore, 
caching and precomputation
+can be done for optimizing search indices \cite{li03feasibility}. Regular 
compression algorithms,
 Bloom filters \cite{362692}, vector space models 
\cite{CuencaAcuna2002DSIWorkshop} and view 
 trees \cite{Bhattacharjee03resultcache} can be used for even better 
optimizations. Authors 
 in \cite{li03feasibility} use Gap compression \cite{wittengigabytes}, Adaptive 
Set Intersection \cite{338634}  
@@ -1205,8 +1206,8 @@
 Peer-to-Peer system is \emph{never} in ''ideal'' state as it is always 
evolving system.
 
 Current research has been focused on system management of tightly structured 
systems, since all presented
-algorithms of tightly structured approach have been analyzed under static 
simulation environments. Furthermore, propsed tightly structured
-overlays are configured statically to achieve the desired reliability even in 
uncommon and adverse environment
+algorithms of tightly structured approach have been analyzed under static 
simulation environments. Furthermore, proposed 
+tightly structured overlays are configured statically to achieve the desired 
reliability even in uncommon and adverse environment
 \cite{rowston03controlloingreliability}. The most important factor for
 future research is to get real-life experiences from tightly structured 
system, when there are frequent
 joins and leaves in the system. Some research has been done already in this 
area. 
@@ -1220,7 +1221,7 @@
 more efficient analytical tools for modelling complex Peer-to-Peer system. 
 
 Some research has been done with regard to load balancing properties of 
tightly structured
-overlays. Byers et al. suggest "power of two choices" whereby an item is 
stored at the less loaded 
+overlays. Byers et al. suggest "power of two choices" whereby data item is 
stored at the less loaded 
 of two (or more) random peer alternatives \cite{byers03dhtbalancing}. Rao et 
al. uses virtual servers
 to control load balance in Peer-to-Peer systems \cite{rao03loadbalancing}. 
Their work rests on
 idea which was originally introduced by Chord \cite{stoica01chord} system.
@@ -1232,8 +1233,8 @@
 therefore enabling peers to find nearby data without looking up data from 
distant peers.
 
 As mentioned before, an implicit assumption of almost every tightly structured 
system is that there is random, uniform 
-distribution of peer and key identifiers. Even if participating peers are 
extremely heterogeneous in
-face of computing power, or network bandwidth, data items are distributed 
uniformly. Clearly, this
+distribution of peer and key identifiers. Even if participating peers are 
extremely heterogeneous, e.g., in
+face of computing power or network bandwidth, all data items are distributed 
uniformly. Clearly, this
 a serious problem of tightly structured overlays in face of performance and 
load balancing. Measurement study 
 by Saroiu et al. shows that there is extreme heterogeneity among participating 
peers in already deployed Peer-to-Peer 
 systems \cite{saroiu02measurementstudyp2p}. Symphony seems to be the first 
tightly structured overlay system 
@@ -1264,7 +1265,7 @@
 \subsection{Programming guidelines and benchmarks}
 
 All existing Peer-to-Peer systems have rather different interfaces even they 
have common points and 
-components. More important, all existing Peer-to-Peer systems incompatible 
with each other. One
+components. More important, all existing Peer-to-Peer systems are incompatible 
with each other. One
 of the most important area of future research is to create common programming 
abstractions, i.e.,
 interfaces, design patters and frameworks. Also, equal benchmarks are needed 
for comparing
 different algorithms. Recently, there have been few proposals towards common 
programming
@@ -1274,7 +1275,7 @@
 \subsection{Social behaviour}
 
 Frequent assumption in Peer-to-Peer systems is that peers are willing to 
cooperate. Another belief 
-is that all peers would behave equally, i.e. all peers both consume resources 
and contributes resources.
+is that all peers would behave equally, i.e., all peers both consume resources 
and contributes resources.
 However, these assumptions are not true as several studies show peers rather 
consume than contribute and
 and peers are unwilling to cooperate \cite{saroiu02measurementstudyp2p}, 
\cite{oram01harnessingpower}, 
 \cite{hearn02mojonation}. 
@@ -1300,7 +1301,7 @@
 rates.
 
 As long as global simulations of Peer-to-Peer systems are lacking, we cannot 
we make any further
-analysis e.g., on usage patterns in Peer-to-Peer systems. Presumedly, however, 
we can assume that
+analysis e.g., on usage patterns in Peer-to-Peer systems. However, we can 
assume that
 , e.g., query keywords follow the Zipf-like distributions 
\cite{breslau98implications} both in the 
 Internet and in Peer-to-Peer systems.
 
@@ -1678,7 +1679,7 @@
 Xanalogical storage \cite{nelson99xanalogicalneeded} is a different kind of 
model for 
 presenting data and relationships between data. While in World Wide Web links 
are
 between \emph{documents}, in xanalogical model links are between individual 
-\emph{characters}. Indeed, each character in xanalogical storage model has a
+\emph{characters}. Each character in xanalogical storage model has a
 permanent, globally unique identifier. For instance, let's consider the 
following
 scenario: ''the character 'D' typed by Janne Kujala on 10/8/97 8:37:18''. In 
this
 example, when character 'D' is is first typed in, xanalogical storage model
@@ -1697,9 +1698,9 @@
 \emph{Enfilade} can be considered as a ''virtual file'' (or part of one), 
which is a list
 of fluid media contents. In xanalogical storage model, links between content 
are external 
 and bidirectional. Xanadu link is an \emph{association} of two enfilades, such 
as an 
-annotation to a specific part of a another document. Transclusion is an 
inclusion in an 
-enfilade of contents already used in another enfilade, i.e. current fluid 
media is copied into 
-different data contents. By using this mechanism, system implementing 
xanalogical model
+annotation to a specific part of a another document. \emph{Transclusion} is an 
inclusion in 
+enfilade of contents already used in another enfilade, i.e., current fluid 
media is copied into 
+different data contents. By using this mechanism, system implementing 
xanalogical storage model
 is able to show all data content that share same fluid media with current data 
content
 (e.g., all documents containing current document's text). Figure 
\ref{fig:xanalogical_model}
 illustrates xanalogical storage model with documents, text and characters.
@@ -1749,9 +1750,9 @@
 associated with a collection of \emph{pointer blocks}. Each pointer block has 
a single 
 target for the pointer. In figure \ref{fig:storm_model}, we present overal 
 pointer creation process. Pointer block may contain zero or more obsoleted 
-pointer blocks, i.e. when a new version of scroll block is created, it 
supersedes 
+pointer blocks, i.e., when a new version of scroll block is created, it 
supersedes 
 one older version which has been created in the past. The most current pointer 
-block will 'obsolete' the pointer block targeting the supersed version. Next 
+block will 'obsolete' the pointer block targeting the superseded version. Next 
 time, when the pointer is used for refering to a specific scroll block, only 
 the most recent pointer's block target is loaded.
 
@@ -1769,8 +1770,8 @@
 We start by giving a problem overview when considering Fenfire in Peer-to-Peer
 environment. We define Fenfire's special needs and evaluate existing 
 Peer-to-Peer approaches in light of these requirements. After that, we propose 
system
-model for Fenfire in Peer-to-Peer environment, present simple algorithms to 
perform data 
-lookups in Peer-to-Peer environment. Also, we discuss possible problems of 
using Fenfire
+model for Fenfire in Peer-to-Peer environment and present simple algorithms to 
perform data 
+lookups in Peer-to-Peer environment. In the end, we discuss possible problems 
of using Fenfire
 in Peer-to-Peer environment
 
 
@@ -1837,10 +1838,10 @@
 feature is almost analogical to Fenfire's (and xanalogical storage model's) 
way of 
 handling data. Another key feature of tightly structured overlays is that they 
are able
 to provide general purpose \emph{interface} for Reference Resolution Services 
(RRS)\footnote{
-Currently, Domain Name System (DNS) \cite{rfc1101} is widely used RRS system 
in the Internet.}
+Domain Name System (DNS) \cite{rfc1101} is widely used RRS system in the 
Internet.}
  \cite{balakrishnan03semanticfree}. Authors argue that next generation RRS 
must be 
 application-independent and references itself should be \emph{unstructured} 
and 
-\emph{semantic free}. Finally, with tightly stuctured systems, it is feasible 
to 
+\emph{semantic free}. Finally, as said, with tightly stuctured systems, it is 
feasible to 
 perform \emph{global} data lookups in the overlay. To summarize, these aspects 
may be the most important features 
 of Peer-to-Peer infrastructure with regard to Fenfire as a \emph{distributed} 
hypermedia system.
 Thus, we see the tightly structured approach the best alternative to locate 
data in Peer-to-Peer
@@ -1898,8 +1899,8 @@
 
 For better fault tolerance and self-monitoring for Fenfire, we propose 
techniques
 presented by Rowston et al. \cite{rowston03controlloingreliability}.  With 
these 
-techniques, we can ensure the performance of Fenfire in a highly adverse 
environment, such
-as extreme heterogeneous, higly dynamic environment or network partition.
+techniques, we can ensure the performance of Fenfire in a highly adverse 
conditions, such
+as sudden network partition, or highly dynamic and heterogeneous environment.
 
 Finally, for more efficient data transfer, we can use variable techniques for 
this purpose.
 For small amounts of data, HTTP can be used \cite{rfc2068}. For big downloads, 
we can use
@@ -1908,9 +1909,9 @@
 
 \subsection{Algorithms}
 
-We use DOLR abstraction of tightly of structured approach, i.e. each 
participating peer hosts 
+We use DOLR abstraction of tightly of structured approach, i.e., each 
participating peer hosts 
 the data and overlay maintains only the \emph{pointers} to the data. We 
descided to use DOLR in our
-model, since DOLR systems locate date without specifiying a storage policy 
explicity \cite{rhea03benchmarks}. 
+model, since DOLR systems locate data without specifiying a storage policy 
explicity \cite{rhea03benchmarks}. 
 DHT based storage systems, such as CFS \cite{dabek01widearea} and PAST 
\cite{rowstron01storage}, may have
 critical problems with load balancing in highly heterogeneous environment. 
This problem is caused by peers 
 which may not able to store relative great amount of data with key/value pair, 
assigned randomly by 
@@ -1936,8 +1937,8 @@
 \begin{itemize}
 \item Data lookup with a given identifier of Storm scroll block.
 \begin{enumerate}
-\item Submit query using scroll block's identifier.
-\item Repeat until hosting peer is found: each peer forwards the query to a 
closer peer which hosts the given scroll block identifier.
+\item Submit data lookup using scroll block's identifier.
+\item Repeat until hosting peer is found: each peer forwards the data lookup 
to a closer peer which hosts the given scroll block identifier.
 \item Pointer peer returns most recent pointer block's value (e.g., hosting 
peer's IP-address) to query originator.
 \item Query originator requests hosting peer to return the scroll block.
 \end{enumerate}
@@ -1952,7 +1953,7 @@
 \item Data lookup with a given pointer random string returning most recent 
scroll block.
 \begin{enumerate}
 \item Query originator locally compute a hash for given pointer random string.
-\item Repeat until hosting peer is found: each peer forwards the query to a 
closer peer which hosts the given hash of pointer random string.
+\item Repeat until hosting peer is found: each peer forwards the data lookup 
to a closer peer which hosts the given hash of pointer random string.
 \item Pointer peer returns most recent pointer block's key/value-pair (e.g., 
hosting peer's IP-address) to query originator, using pointer block's own 
indexing schemes. 
 \item Query originator requests hosting peer to return the scroll block.
 \end{enumerate}
@@ -1963,7 +1964,7 @@
 \begin{enumerate}
 
 \item Query originator locally compute a hash for given pointer random string.
-\item Repeat until hosting peer is found: each peer forwards the query to a 
closer peer which hosts the given hash of pointer random string.
+\item Repeat until hosting peer is found: each peer forwards the data lookup 
to a closer peer which hosts the given hash of pointer random string.
 \item Pointer peer returns pointer block's key/value-pair(s) (e.g., hosting 
peer's IP-addresses) to query originator, using pointer block's own indexing 
schemes. 
 \item Query originator requests hosting peer to return the scroll block.
 \end{enumerate}
@@ -1972,7 +1973,7 @@
 Figure \ref{fig:storm_query_urn5} illustrates how Storm scroll block is 
located 
 in a tightly structured overlay using DOLR method, where pointer random string 
is known.
 
-Each of these algortihms can locate Fenfire related data in $\Theta(\log{n})$ 
time:
+Each of these algortihms can locate Fenfire related data in $O(\log{n})$ time:
 $O(\log{n})$ time for query routing to pointer peer and constant time for 
 locating hosting peer with a given reference link. Time required for 
transferring
 the data is not included.
@@ -1996,7 +1997,7 @@
 \subsection{Problems}
 
 Perhaps the most biggest issue in Peer-to-Peer systems is non-maturity of
-secure techologies. For instance, online entities cannot be identified 
+security techologies. For instance, online entities cannot be identified 
 safely (e.g., the Sybil attack \cite{douceur02sybil}). For Fenfire, one
 security related problem occurs when user wants to perform global data lookup 
with a given
 pointer random string; how user is able to verify the correctness
@@ -2004,11 +2005,11 @@
 correct Storm scroll block ? Spam attack \cite{naor03simpledht} is a variation 
of previously
 mentioned problem; data lookup is performed by a user, but there is no reply
 from the system. How do we are able to know if this was a spam attack, or the
-data really no exist in the system ? Another problem related to Fenfire's 
+data really doesn't exist in the system ? Another problem related to Fenfire's 
 security is that if a user downloads data from the network to local computer 
 and after network disconnetcion, user wants to verify \emph{offline} the 
 authenticity of data. Obviously, optimal solution to all security issues would 
-be that digital signatures are included to every message sent in the system. 
+be that digital signatures are included to every message sent to the system. 
 However, these problems are not only limited to Fenfire, it concerns all 
 Peer-to-Peer based computer systems.
 
@@ -2023,7 +2024,7 @@
 we divided open problems into three sub-categories: security related problems,
 performance related problems and miscellaneous problems. Each of these
 sub-categories have number of open problems, in which there are no solutions
-yet, or solutions are only partial. Much research work is required to
+yet, or solutions are only partial. We point out that much research work is 
required to
 solve open problems.
 
 Then, we focused our attention to Fenfire system. First, we gave a brief
@@ -2032,12 +2033,13 @@
 
 In last chapter, we evaluated existing Peer-to-Peer approaches with regard
 to Fenfire's needs. We proposed, that tightly structured approach is the
-best alternative to our needs for the following reasons. First, Storm, 
xanalogical
+best alternative to Fenfire's needs for the following reasons. First, Storm, 
xanalogical
 model and tightly structured systems use global unique identifiers
 for identifying data. Second, our Storm design uses semantic-free references
-for locating data in distributed networks. As the authors of 
\cite{balakrishnan03semanticfree},
-we also observe that tightly structured overlays provide general purpose
-interface to next-generation reference resolution services. Second, by using 
+for locating data in distributed networks generated by SHA-1 cryptographic 
content
+hash \cite{fips-sha-1}. As the authors of \cite{balakrishnan03semanticfree},
+we also agree that tightly structured overlays provide general purpose
+interface to next-generation reference resolution services. Third, by using 
 DOLR abstraction of tightly structured overlay, we can minimize the the lack 
 of locality in tightly structured overlays. Finally, we believe that issues 
 related to tightly structured overlays are solved in near future, because of