Open, Ongoing, and Finished Theses

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Survey and Comparison: Complexity Reduction in Graphs to support the Visualisation of Big Data

Bachelor Thesis, Master Thesis, Student Research Project

finished


Most data can be structured as graph, e.g., social networks, collaboration information, ancestry-information. As the complexity of such data is growing, we are running into trouble when we want to understand the information we get from a piece of data. Therefore, we need to reduce the complexity  of the data to get the overall picture. There are approaches to reduce the complexity of data by introducing a reduction by pooling. In this thesis, we want to survey and compare these reduction approaches.

BSVF: Botnet Surveillance Visualization Framework pt. 1

Bachelor Thesis, Master Thesis, Diploma Thesis, Student Research Project

finished


You should design and develop a P2P botnet visualisation framework with the following tasks

 

  • Implement your framework with the help of the OGRE 3D Graphics Engine
  • Link your framework with the SNAP dynamic network analysis tool
  • Usage of known graph layout algorithms, e.g. ForceAtlas and Random Layout
  • Apply your tool using real P2P botnet monitoring data

BSVF: Botnet Surveillance Visualization Framework

Bachelor Thesis, Master Thesis, Diploma Thesis, Student Research Project

finished


You should design and develop a P2P bonnet visualisation framework with the following tasks

 

  • Implement your framework with the help of the OGRE 3D Graphics Engine
  • Link your framework with the SNAP dynamic network analysis tool
  • Usage of known graph layout algorithms, e.g. ForceAtlas and Random Layout
  • Apply your tool using real P2P botnet monitoring data

Die Stadt Darmstadt stellt im Rahmen des da_sense Projekts die Daten der Inktionsschleifen von allen Kreuzungen in und um Darmstadt bereit. Diese Daten beinhalten Anzahl der gemessenen Autos und die Belegzeit der Induktionsschleifen.

Wir wollen diese Daten zu einem dynamischen Graphen kombinieren und mit graph-theroretischen Metriken versuchen Verkehrsstörungen wie Stau und Unfälle zu erkennen.

  • Verknüpfe die Kreuzungen und Sensoren um einen Graphen der Kreuzungen & Straßen zu erhalten.
  • Erstelle ein Modell des Straßennetzwerks der Stadt Darmstadt
  • Analysiere die Verkehrsdaten mit graph-theoretischen Metriken

Improving Topology Control for Wireless Sensor Networks

Master Thesis, Bachelor Thesis

finished


By reducing the communication range of nodes in wireless sensor networks, we can achieve significant savings in energy consumption. However, changing the network structure typically increases the shortest path length between communication partners. Traditional approaches do not consider this for decision-making.

A Smart Space Environment enables the user to use smart devices and services in an advanced manner. We need to define interfaces and protocols in order to allow the seamless usage and easy development.

A major difficulty is the heterogenous environment, the participating devices and services are likely to be developed using different programming languages (e.g. Android and iOS, Windows and Unix). The interface and protocol description should be capable to support these different platforms. 

 

The following tasks should be processed:  

  • Survey of possible description techniques
  • Define necessary interfaces and protocols
  • Implement interfaces and protocols 

This thesis is co-supervised by Florian Müller (TK).

 

 

Connecting multiple Smart Spaces

Master Thesis

finished


A Smart Space Environment enables the user to use smart devices and services in an advanced manner. A single Smart Space is restricted to a „small“ network environment. We need to connect multiple smart spaces in order to allow the user to use smart services in a remote smart space.

This interconnection of multiple smart spaces reveals some challenges. How to establish this connection? How to secure a connection between multiple smart spaces? How to establish the used publish-subscribe paradigm in a „global“ network? 

 

The following tasks should be processed: 

  • Analyse the problem of global pub/sub and common solutions
  • Develop global pub/sub connection for uMundo
  • Define a basic security model 

Wireless Video Streaming

Bachelor Thesis

finished


Suppose you want to stream high quality media data within your wireless environment at home. Which codecs are performing best? Which codecs are avoiding to congest your network? 

This thesis aims on the analysis of various video codecs to analyze the quality of transferred video data, the latency and the necessary bandwidth. We have a basic application to stream data using uMundo, based on this application we want you to add and evaluate different video codecs.

Detecting Darknet Bridges

Bachelor Thesis

finished


Freenet is a P2P system that aims to provide anonymity and censorship-resilience. In addition, Darknet participants achieve membership-concealment by only connecting to trusted peers. Opennet participants, on the other hand, connect to both trusted and arbitrary peers. Opennet and Darknet are hence interconnected. Detecting Opennet participants with Darknet neighbors (called Bridges) would allow an attacker to disconnect both networks by compromising said participants. Preliminary measurements Bridges exhibit a different behavior from other Opennet peers. In the thesis, the task is to analyze if this beahvior is distinct enough to detect such Bridges. Changes should be suggested in order to hide Bridges.

Goal of this thesis it the development of a browser plugin that allow the user to easily generate simple web crawl directives and parsers for web pages.

Analyzing Dynamic Sampled Graphs

Bachelor Thesis

finished


Die Motivation hinter dieser Bachelorarbeit ist es, eine Office-Integration für die private Cloud zu entwickeln, die nicht auf externe Server zum Speichern zugreift. Somit ist es für den Endnutzer möglich zu Hause auf seinem eigenen Speicher Dateien ohne Sicherheitsbedenken so wie bei öffentlichen Anbietern wie Dropbox zu archivieren (Wo sind meine Daten? Wer hat darauf Zugriff? Wozu werden meine Daten genutzt? …). Zudem ist es nicht mehr nötig, auf jedem Gerät, das auf die Cloud zugreift, eine Office-Anwendung installiert zu haben, um seine Dokumente anschauen und bearbeiten zu können. Mit der App-Erweiterung der privaten Cloud um eine Office-Integration ist es möglich, bequem auch unterwegs mit dem Smartphone oder Tablet, von zu Hause mit dem Laptop oder auch auf der Arbeit mit dem Desktop-Rechner auf seine Daten sicher zuzugreifen und diese kurzerhand zu öffnen und zu bearbeiten.

Peer-to-peer video streaming systems that are deployed in real life situations are faced with extremely heterogeneous environments. These are environments in which peers can fail and join or leave the system at any time. Also peers can have very different and changing bandwidth capacities. Peer-to-peer video streaming systems should ideally cope with these requirements while still offering a fast and reliable service.

In this thesis, a multi-tree push system will be implemented in the OMNeT++ framework. Next, we will perform a parameter study to see how the system behaves in heterogeneous environments. Furthermore, we will investigate how local knowledge about the bandwidth capacity of peers can be used to get more accurate cost/gain functions to construct more efficient topologies.

The analysis of Online Social Networks and similar services requires the acquisition of large data sets. Commonly, distributed web crawlers are used to collect this kind of information. The distribution is required to circumvent rate limiting employed by the service provider and avoid bottlenecks with network communication.

Web crawlers are simple programs that fetch data as specified by an input such as downloading a file from a given URL. Depending of the task at hand, the data can be post-processed and potentially imply the download of further data. Commonly, a central entity provides commands or tasks to a set of workers that perform the tasks and return the results. This central server then aggregates the results and creates further tasks based on failed tasks, the returned results, and recurring requirements.

In previous work, we designed and implemented such a framework for the distribution of tasks from a central entity to a set of workers (Task Distribution Framework). While it supports all actions required for the execution of the aforementioned workflow, it does not include a simple way to record and output statistics. Also, the deployment of multiple parallel crawls has to be done by changing configuration files by hand.

The goal of this thesis is the extension of the Task Distribution Framework by logging and statistics capabilities. Furthermore, a web front-end should be created to display the generated statistics and the system status. Finally, a basic administration interface for managing different projects inside the framework should be created and deployed on our infrastructure, currently consisting of 15 dedicated crawling machines.

The tasks of this thesis will be to:

  • Understand the concepts of the Task Distribution Framework
  • Design and implement logging and statistic components
  • Design and implement an administration front-end
  • Deploy and test the framework on our infrastructure

 

 

 

Peer-to-Peer (P2P) networks currently make up for a major share of the overall traffic on the Internet. They act as a medium for the exchange of a wide variety of content, ranging from comparibly small pictures or music files to voluminous content like complete software packages, linux distributions, or movies or similar types of multimedia content.

Generally, P2P networks do not account for the location of different peers, which may lead to a rather inefficient usage of networking resources. This has an affect both on the achievable performance, seen at the participating devices, and on the management and resource disposition of the Internet Service Providers (ISP). The latter may suffer serious disadvantages with respect to their peering cost or may experience bandwidth limitations for competing services and content. In consequence, ISPs have started to introduce shaping of P2P traffic, or even to attempt blocking P2P traffic completely, which has lead to an arms race between developers, who have started to conceal P2P traffic, and the ISPs that are trying to again identify it.

Keeping P2P traffic local in their network may lead to a partial relief for the ISPs. However, ISPs are not in the position to cause significant changes to the protocols and applications used for P2P networking. Replicating and serving the requests from local resources, much alike the content distribution approach implemented for web caching, may be a possible solution. With the volume of the distributed content being on orders of magnitude higher than for conventional web pages, and knowing of the drastically differing popularity of the content, a sensible selection of replicated data has to be identified. As the popularity can change very quickly, it preferably has to be identified very fast, or if possible, even before the rush of requests has taken place on the local network.

 To achieve this estimation of a set of the most popular content in the existing P2P networks, an efficient and non-intrusive distributed monitoring infrastructure is needed.

05.12.2011

Angriffsanalyse von P2P Overlay Netzwerken

Master Thesis

finished


Structured Peer-to-Peer (P2P) overlays like Chord, CAN, Pastry, and Kademlia provide means to build self-organized system for diverse application like P2P-based massively multiplayer online games (MmoG), distributed online social networks (DOSN), streaming applications (e.g., PPLive, PPStream, etc.), and file-sharing applications (eMule, Bittorent, etc.).  mechanism to support distributed applications. In order to locate any object, these structured overlays maintain routing tables with small number of entries. They are scalable and resilient to faults, dynamics and loads.
    In open environment it is highly probable that the benignity of these overlays is thwarted by adversarial behavior, not only from insiders peers but also from outsider adversary. To insure the self-organization of peer nodes and validity of the systems, these overlays must be able to respond adversaries. For instance, adversaries may mis-route, corrupt, manipulate, drop messages or data and routing information. They may acquire more Ids to disrupt, manipulate, or control system functions. They may collude with other peers to orchestrate denial of service attack on the P2P-based applications and system.
    In this thesis we analyze structured P2P overlays for security threats. We will focus on those design decisions or/and deficiencies which could lead attacks on the system. We will try to answer that:

  • What is(are) the most efficient attack(s) to disrupt performance of these overlays?
  • What is/are the countermeasure(s) to handle these attacks on P2P overlay?

Live streaming systems either centralized or P2P-based ones are challenged by the ash crowd phenomenon. It is reported that during the rst few minutes of a live streaming session, there are hundreds of thousands of users 1 trying to join the session. Based on simulations, this study investigated the ability of DONet, a representative pull-based P2P live streaming system to mitigate ash crowds with respect to di erent sizes of the initial population in the system. To better deal with the phenomenon three modi cations to the system's protocol were also proposed and evaluated.

As the popularity of video live streaming through the Internet continuously rises, lots of efforts have been made to reduce the delays and increase user experience. In this thesis, we focus on delay reduction and load balancing of peers in multi-tree based live video streaming overlays. Multi-tree overlays are designed to reduce delays, but do not guarantee the best possible results without optimization strategies, as peers with high bandwidth can be leafs, whereas low bandwidth can be interior nodes.

Missing load balancing can lead to situation, where peers have to serve more children than their upload capacity can handle. This can dramatically reduce the quality of user experience, resulting in video stalls. If such a situation occurs near the root of a tree, huge part of the overlays can suffer from that, as peers have to forward the received video segments.

We implement two different optimization strategies, handling insufficient bandwidth situations and trying to improve the topology in free bandwidth situations. One strategy focusses on the bandwidth situation of neighbored peers, called bandwidth aware strategy. The main focus of that strategy is to reduce delays by reducing average tree heights and balance load by reflecting current bandwidth situations. The second strategy is designed to reduce neighbor delays by connecting peers with locally close other peers. This strategy is called location aware optimization strategy.

In order to show that our strategies reduce delays or balance load, we evaluate them by using 49 distributed physical machines, grouped in German Lab. An measurement system is implemented, collecting data about the topology is used to clarify the benefits of our strategies, compared to the random approach. Our results show that bandwidth awareness in most of the cases reduces average delays and upload utilizations by moving high bandwidth peers towards the root, which increases the tree height. With the location aware strategy we show that delays to directly connected neighbors are reduced, which also leads to a reduction of average delays in the tree topology.

31.12.2013

Sampling-based network analysis

Master Thesis

finished


30.09.2013

Cloud Storage System

Bachelor Thesis

finished


Anonymous Peer-to-peer systems, also called Darknets, have been a topic of interest both in research and society during the last few years. Routing on such networks is particularly challenging, since it has to rely on nothing but local information and the number of links is typically small in comparison with other social networks. Moti- vated by an undirected small world model, we introduce a Lookahead routing strategy using IDs that are chosen with regard to local struc- tures. Simulations show that our algorithm has more than twice the success rate than the one used in the current version of Freenet - to our knowledge the only system satisfying the requirements of a Darknet - at the price of a slightly higher cost per step.

14.09.2012

Measuring Freenet

Master Thesis

finished


Darknets experience growing popularity. Their users object to the in- creasing restriction of freedom of speech and invasion of privacy by govern- mental institutions and companies. Therefore, they participate in darknets to anonymously share information with others. One of the most popular darknets is Freenet. It provides distributed le storage and uses indirect routing in order to protect the identities of content consumers and providers. In addition to its Opennet mode where nodes connect to strangers, it also o ers a Darknet mode in which a node can only connect to peers it trusts. Freenet is the only popular system providing a sucient level of anonymity 8 and privacy for its members. However, since its release in 2000, only a few studies have been made to examine the behavior of Freenet nodes and the network as a whole.
In this master thesis, we conduct measurements in Freenet in order to test several hypotheses about its functioning. In particular, we give an estimation of the size of Freenets Opennet network and its structure. Therefore, we re- construct and analyze the topology in the Opennet. Moreover, we monitor user behavior and estimate churn rates and online times of single nodes. In addition, we look at the routing of le requests and their content. Complementing these Opennet measurements, we conduct a small Darknet measurement as well. We observe in particular the behavior of bridge nodes connecting the Darknet with the Opennet.

09.02.2012

Graph Drawings as Embeddings for Routing

Bachelor Thesis

finished


Routing in distributed networks, where the network structure with nodes and links between them is not to be modi ed, requires an identi er space such that each vertex has a coordinate, in contrast to other networks where routing tables help to choose the next hop to forward a message to. Graph drawing algorithms can handle the regular computation and assignment of coordinates. Although primary designed after visual aesthetics, we will simulate and analyze their eld of application for routing purposes on graph models and existing real world networks.

Zur Zeit erfreuen sich Live-Streaming-Systeme einer immer hoheren Beliebtheit. Da aber die klassische Client-Server-Architektur durch die steigende Anzahl von Nutzern nicht gut skaliert, wird oft auf eine Peer-to-Peer basierte Losung zuruckgegri en. Daher wurde auch an der TU Darmstadt ein solches System entwickelt. Allerdings ist dieses, wie auch andere auf Peer-to-Peer basierten Systeme, wegen seiner Komplexitat nicht leicht zu analysieren. Deswegen wurde im Rahmen dieser Arbeit ein Monitoring Server fur dieses existierende Peer-to-Peer-Streaming-System entwickelt. Dieser Monitoring Server stellt das Netzwerk gra sch da und kann in dieses auch aktiv eingreifen. Dadurch kann das Netzwerk besser analysiert und getestet werden.

15.05.2012

Communities and Roles in Wireless Networks

Bachelor Thesis

finished


Communities and roles are useful properties to analyze the structure of networks and can be used to improve routing algorithms, but so far the calculation of these properties needs global information. Good algorithms for wireless networks have to rely solely on locally available information, because the aggregation of global information generates a high message overhead. In this thesis we evaluate how roles and communities can be detected in wireless networks with minimal global information. We modify an existing community detection algorithm to run without global information and evaluate a universal role de nition on wireless networks. We also proof that the number of communities in the neighborhood of each node is bound from above and introduce a new role de nition for wireless networks. We evaluate the algorithm and role de nition on a realistic generation model for wireless networks, as well as on a random generation model for wireless networks.

01.06.2012

Knowledge-based Data Access in Facebook

Bachelor Thesis

finished


The Internet and especially social networks connect people in this world. In the simplest way information, pictures and news can be shared with friends, acquain- tances or relatives. Using pro les, fan groups and other functions, humans are transparent persons to their friends. But it does not matter if the friend is a close friend, a college romance or maybe ones super- visor. This thesis deals with this problem and tries to exclude persons from 5 information based on the degree of friendship. In the same way, it should be possible that people can share information without a direct Facebook friendship. This would make it possible that old school friends who have a certain degree of knowledge about this person, acquires new information. The aim of this thesis is to develop a program that meets these requirements. No existing program is able to cover these functions.
A Firefox extension which uses the Facebook API was written and includes several encryption procedures. These components are discussed further in Chapter 2. To get an overview of the program, Chapter 3 describes and explains the various parts of the development process. Possible further developments of this work are mentioned in Chapter 4. The Firefox extension is called KDAF and is tested under the operating system Microsoft Windows 7 and Linux Ubuntu.

31.07.2012

Development of a Task Distribution Framework

Bachelor Thesis

finished


When working on scienti c or commercial projects, problems can occur that can not be solved by a single machine, e.g., due to the amount of required computational power or bandwidth limitations. However, it is often possible to divide the problem into smaller sub-problems, which can be solved independently by many di erent machines. The results of these sub-problems are then combined to solve the overall problem. Developing applications supporting distributed problem solving can be a tedious task. Therefore it is reasonable to abstract the implementation of the actual problem solving from the functionality to distribute sub-problems and accumulate their results. Depending on the requirements of the problem, systems and libraries that provide such abstraction require di erent features. In this thesis, the requirements include the focus on simplicity and the independence from the actual implementation of the problem-solving application. According to these points, a complying framework is designed and implemented. Two example applications using distributed problem solving are created to show the applicability of the implementation according to the previously described requirements. In addition to this, di erent approaches regarding this topic are presented, and the designed framework is compared to appropriate related work.

01.08.2012

Graph theoretic approach to network resilience

Bachelor Thesis

finished


A graph theoretic approach to network resilience is presented in this thesis. Finding an ideal delete cover for a graph belongs to the NP-Complete class of problems. Heuristic derived from the Fiedler vector of a graph is derived and tested on simulations.

As the Internet becomes increasingly important to all aspects of society, its disruption has many bad consequences. Hence it is necessary to increase the resilience of the Internet. We de ne resilience as the ability to work well, although a set of nodes of the network are removed. But it was not well
analyzed how the Internet behaves against the node removals. The purpose of this thesis is to create many attack scenarios based on various types of node removals and resilience metric. Then we use the results to analyze the resilience of the Internet.


In this thesis we analyze the networks behavior against node removals using two types of metric. The rst is based on the partition, such as the giant component, and the second on the path lengths of the networks, such as the average shortest path length. There are also two types of node removals, using a random attack and intentional attack. In the intentional attack scenario, we have di erent ways to choose the deleted nodes, one is based on the network global properties and the other is based on the local properties of each node on the network.


The result shows that we must combine these two types of metrics to have a best view on the networks. The partition based metrics give us the information when the network is fragmented, we call this point as the critical point, and the shortest paths based metrics show us more information about
the network behaviors from the beginning to this critical point. The result also indicates that the degree and betweenness centrality removals are the most ecient methods. They can nd the most vital nodes in the network. The random node removal nearly has no impact on the network. Such an analysis is not analyzed. In this thesis, all of the metrics, the attack scenarios and the network generators are taken together to get a better knowledge about them.

Der Clustering-Koezient ist eine Metrik, die bei der Analyse von Graphen benutzt wird. Durch diese Metrik wird ausgedrückt, wie viele der Nachbarn eines Knotens untereinander verbunden sind. Speziell bei Graphen 2 aus sozialen Netzwerken wird diese Metrik sehr häuggiu g eingesetzt, da hierbei der Clustering-Koezient Aussagen über die Beziehungen der Benutzer untereinander ermöglicht.
Die Berechnung des Clustering-Koezienten unter Verwendung bekannter Verfahren, ist allerdings sehr speicher- und rechenintensiv und kann dementsprechend nur auf Maschinen mit viel Speicher berechnet werden. Das Ziel dieser Arbeit ist es, ein möglichst speicherezientes Verfahren zu fi nden, mit welchem die Berechnung des Clustering-Koezienten auch auf Maschinen mit wenig Speicher möglich ist.
Da es auf den Maschinen mit wenig Arbeitsspeicher nicht möglich ist den gesamten Graphen im Speicher zu halten, benutzen wir für unseren Ansatz einen Cache. Dieser besitzt allerdings eine beschränkte Kapazität und somit können nur eine begrenzte Anzahl an Einträgen zwischengespeichert werden. Deswegen ist es wichtig, diesen möglichst effizient zu organisieren. Für diese Organisation verwenden wir verschiedene Caching-Strategien. Die Berechnung erfolgt dabei auf Graphen aus sozialen Netzwerken. Graphen aus sozialen Netzwerken besitzen die Eigenschaft, dass Nachbarn eines Knotens strker miteinander verbunden sind als bei Graphen aus anderen Netzwerken. Demnach besitzen Knoten untereinander viele gemeinsame Nachbarn. Durch verschiedene Abarbeitungsreihenfolgen wird deshalb die Reihenfolge, wie die Knoten bearbeitet werden, so verndert, dass die nacheinander berechneten Knoten eine mglichst groe und gemeinsame Nachbarschaft besitzen. Dadurch kann die begrenzte Kapazität des Caches besser ausgenutzt werden.
Insgesamt haben wir 5 Abarbeitungsreihenfolgen und 5 Caching-Strategien auf Graphen aus sozialen Netzwerken getestet. Durch die Kombination dieser verschiedenen Strategien und einer Erweiterung für 3 Abarbeitungsreihenfolgen, haben wir entsprechend 40 verschiedene Kombinationen aus Abarbeitungsreihenfolge und Caching-Strategie getestet. Dabei konnte eindeutig nachgewiesen werden, dass die Abarbeitungsreihenfolge einen deutlichen Einfluss auf die Eff ektivität des Caches und die Laufzeit der Berechnung hat.

The global clustering coecient (gcc) is an important metric to analyse graphs. For large graphs, absolute approaches are not feasible, since all current absolute approaches have a high computing complexity and mostly a large memory footprint due to matrix-based calculations. In this thesis,
we provide an algorithm to get a fast approximation of the gcc even for big graphs.


In our algorithm, the graph is divided in partitions. For each partition, the absolute gcc is calculated. Each partition gcc is corrected concerning the ratio of existing edges to the maximal possible edges of the partition in relation to the ratio of the complete graph. This relation is the main contribution of this thesis, since it seems not to be previously published. The so corrected partition gccs are averaged, weighted by the node count of each partition.


We compare our algorithm to another previously published approximative algorithm on a broad set of graphs. We show that for most evaluated graphs, we can provide a signi cant faster sucient approximation than the previous work. Since the time-consuming task in our approach, the calculation of the gcc for each partition, is independent for each partition, our approach can be computed easily in distributed systems, what makes it scalable for large graphs.

Securing GnuNet

Master Thesis, Bachelor Thesis

finished


Censorship-resilience and anonymity is not possible in a centralized system, unless one, unrealistically, assumes that the central authority is unconditionally reliable and trusted. GNUnet is a newly developed P2P system, modifying and enhancing the Kademlia DHT to provide anonymity and optionally membership-concealment. Being a hardly tested system, some components are still in need of a thorough security and performance evaluation. The use of a DHT is bound to enable some extent of censorship, as well as complicating responder anonymity. The high number of replicas introduces a high load on the system, which can probably be minimized with at the cost of only slightly reduced availability. In your thesis, you should evaluate one (BSc) or several (MSc) components of GNUnet, as well as suggest and implement improvements.

Measuring Churn in Freenet

Bachelor Thesis

finished


A measurement-based early analysis of the anonymous le-sharing system Freenet has revealed a di erent churn behavior to common P2P le-sharing systems. However, our current data does not suce to develop a in-depth churn model. The task of this thesis is to make detailed and churn measurements considering diurnal patterns. From this data, a churn model for such networks should be constructed and compared with previously found behavior in P2P networks.

30.12.2013

A Darknet Simulation Model

Bachelor Thesis

finished


Darknets, membership-concealing P2P systems designed to achieve censorshipresilience even under extreme adversarial conditions, have been used in the wild for about a decade. However, no event-based simulations have been made, as are needed for the scienti c analysis of such systems. The goal of this thesis is to build a simulation model in OMNET++, which provides the generic functionalities of Darknets. Furthermore, the performance of two early Darknet routing approaches should be compared  within the developed framework.

30.12.2013

Analyzing Freenet Embeddings in a Testbed

Bachelor Thesis

finished


It has been shown that the embedding algorithm of Freenet is vulnerable to various attacks. A more secure alternative has been suggested and analyzed theoretically as well as by simulation. The goal of this thesis is to modify the real Freenet code by integrating the newly developed embedding algorithm and set up a full testbed for evaluating its performance under real-world conditions.

30.04.2013

Detecting of Unplanned Mass Gatherings in Twitter

Master Thesis

finished


Recent examples like the Love Parade show that mass crowd gatherings imply high conflict potential. Especially in emergency situations with no rescue squads on site, identifying these crowds in time is a challenging task. This is even more difficult for spontaneous gatherings. Providing information about such events could help us to understand the situation at hand and finally to increase the situational awareness of decision makers in crisis management.

Complex networks are omnipresent in our daily life. Network structures like Peer-to-Peer (P2P) systems which leverage on distributed resources create highly complex networks and are already established in several application domains. Well-known applications for VoIP, distributed file systems and file sharing like Skype, Freenet and Gnutella are built on top of P2P systems. Skype for example provides its service to over 440 million users as of the first quarter of 2009. Currently, P2P applications are estimated to account for over 60% of the whole Internet traffic with an upward trend. The scientific community has seen a variety of different approaches like CAN, Chord, Kademlia, or Pastry that have inspired many new architectures and systems. The analysis of current approaches and architectures is essential to improve existing approaches and create new topologies for specific purposes.

The simulation of network models is the research tool of choice for a variety of network related research challenges. Nevertheless, with rising popularity of simulations, the credibility of the results has decreased. A survey of MANET simulation studies by Kurkowski et al. found significant unresolved challenges. One key finding is, that a comparison of simulation studies is hardly possible. Only 15% of the simulation studies of the published ad hoc papers between 2000 and 2005 were repeatable. One reason for these drawbacks is that most network simulations focus on dynamic properties like message delay and package loss. Slight differences in the used network simulators or their configuration lead to drastically different results that hardly reflect the differences between network topologies.

While simulations often focus on these dynamic properties, they usually do not consider the structural analysis of the underlying network topology. The graph-theoretic analysis of network snapshot provides a viable contribution to our understanding of complex network structures. It characterizes local and global graph-theoretic properties which determine large parts of a network’s behavior. Well-known metrics like the degree distribution, clustering coefficient and shortest path length distribution can help us to determine the applicability of specific network designs to given problems and identify their flaws and drawbacks in specific scenarios. Since graph-theoretic metrics are precise measures of the considered properties, they allow for a fair comparison of arbitrary network topologies. The main contribution of this thesis is the graph-theoretic analysis of complex networks using the Graph-Theoretic Network Analyzer (GTNA), a framework we created especially for this purpose. We define a set of graph-theoretic metrics and apply them to four structured P2P systems, namely CAN, Chord, PathFinder and Sym- phony. By analyzing the results of these measurements we exhibit strengths and weaknesses of the examined P2P networks. We propose configurations and new methods to enhance the systems and avoid the negative properties we found during our analysis. These findings are applicable to other P2P systems and arbitrary complex network since they are derived from common structural properties that many complex networks share.

15.10.2010

Cryptographic Treatment of Private User Profiles

Bachelor Thesis

finished


Graphs are used to model networks, relations and complex problems, they have therefore gotten a lot of attention in the last years. However, the limits of the insights that can be gained by traditional graph metrics have become apparent. The community structure of a graph promises to give 7 additional insight, the problem of detecting this community structure got a lot of attention in the last couple of years. Various algorithms have been suggested to nd the community structure of a graph. This bachelor thesis takes a closer look at those algorithms, in particular one local and one global algorithm. The algorithms di er in the data that they use to determine the community partition. An algorithms is called local if a node exchanges information only with its neighbor while an algorithm is global if all data is gathered at a central instance. We implement the two algorithms in JAVA and analyze their performance as well as the quality of the community structures they detect. The rst algorithm named LPAExtended [1] is a local algorithm that is based on forwarding information about the community of a node to its neighbours. The second algorithm named deltaQ [2], is a global algorithm that tries to maximize the modularity of the community structure in each iteration. The community structures that each of the algorithms is able to detect are not only compared to each other but also to the best possible community structure for the graph. In order to know the best possible community structure, we use a special graph. This graph has a prede ned community structure that can be changed as needed. We show, that the local algorithm is a lot faster than the global algorithm while still being able to detect a meaningful community structure for reasonable graph con gurations.

26.01.2012

Subsampling of Complex Networks

Master Thesis

finished


This thesis concerns itself with the problem of subsampling of complex networks. The questions we attempt to answer are: Which properties of the original network are preserved? To which extend are they preserved? How does this depend on the algorithm used, including its general properties and speci c parameters? How does this depend on the nature of the original network?
We group known subsampling algorithms together, attempt a classi cation, and sketch new ones where gaps in the classi cation appear. We choose a two-dimensional classi cation based on neighbor selection and dimensional strategy. We end up with 22 viable algorithmic variants. The network met- rics we use are network size, degree distribution, diameter, characteristic path length, and clustering coecient. The networks we subsample are ErdosRenyi, BarabasiAlbert, complete network, and three real-world networks. We carry out the evaluation using and extending a framework for which we newly implement all evaluated subsampling algorithms.
We are able to successfully link certain properties of subsampled networks to categories of subsampling algorithms (as opposed to only individual ones). Such category results include: Network size is primarily determined by neighbor selection and secondarily by dimensional strategy. Diameter and characteristic path length are best preserved overall by three variants of 9 the Depth-First Search algorithm. Cluster- ing coecient is well preserved by subsampling algorithms choosing a nite but nonzero number of neighbors in every step. Algorithms choosing no or all neighbors produce extreme results.

15.05.2012

Communities and Roles in Wireless Networks

Bachelor Thesis

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