Thorsten Strufe

Technical University Darmstadt, Darmstadt, Hesse, Germany

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Publications (72)11 Total impact

  • Hani Salah, Thorsten Strufe
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    ABSTRACT: The autonomous cache management in Content-Centric Networking (CCN) results in suboptimal caching decisions and implies cache-ignorant routing. Cache coordination and similar improvements hence have been the subject of several recent studies. The proposed solutions, however, are either impractical due to their massive coordination overhead, or of limited benefit since they cannot realize perfect coordination. We present CoMon, an architecture for network-wide coordinated caching. CoMon realizes an affordable, yet highly effective, coordination by assigning monitoring and cache-aware (re)routing tasks to only a few nodes, through which the majority of traffic is expected or enforced to pass. CoMon, by design, can maximize the diversity of cached contents and minimize cache replacements. In addition, our simulation study using ISP topologies, shows that CoMon under a pressuring scenario, when coordinates as few as 5% of the nodes, reduces the server hit ratio of both CCN and notable related work by up to 45%. Index Terms: Information-Centric Networking; Coordinated Caching; Cache-Aware Routing
    IEEE CCNC, Las Vegas, USA; 01/2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: Information-centric networks are a new paradigm for addressing and accessing content on the Internet, with Content-Centric Networking (CCN) being one of the more popular candidate solutions. CCN de-couples content from the location it is hosted and allows for mobility of the node requesting the content. However, CCN's ability to handle the mobility of the content source are limited and so far little research has focused on how both endpoints would be able to be mobile. We focus on mobility of the content source, using network embeddings as a tool. Network embeddings have already been proposed for content addressing and mobility management in prior work. In this paper, we first show that previously designed embeddings lead to a highly unbalanced storage and traffic load: More than 90% of all stored references are mapped to one node, which is involved in more than 95% of all queries. We propose a modified embedding, Prefix-S embedding, and a topology-aware key assignment, which enable a uniform distribution of the storage load. The maximum traffic per node is also considerably reduced from more than 95% to 35%.
    09/2014;
  • Giang Nguyen, Mathias Fischer, Thorsten Strufe
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    ABSTRACT: The robustness of pull-based streaming systems to node failure and churn has been extensively analyzed. Their resistance to sabotage, however, is not well understood, so far. Recent measurement studies on a large deployed pull-based system have discovered stable source-to-peer paths and the convergence of the content dissemination to rather static topologies over time. Thus, an attack on central nodes within these static topologies, which causes serious service disruptions, is feasible. This paper demonstrates attacks that significantly reduce the system’s performance. As a countermeasure, we introduce a novel striping scheme, which decreases the dependencies between peers and thus the impact of attacks. A thorough simulation study indicates that our scheme achieves a high resistance against sabotage attacks at negligible overhead and performance penalties.
    International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS), Paderborn, Germany; 09/2014
  • Hani Salah, Stefanie Roos, Thorsten Strufe
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    ABSTRACT: Discovery of nodes and content in large-scale distributed systems is generally based on Kademlia, today. Understanding Kademlia-type systems to improve their performance is essential for maintaining a high service quality for an increased number of participants, particularly when those systems are adopted by latency-sensitive applications. This paper contributes to the understanding of Kademlia by studying the impact of \emph{diversifying} neighbours' identifiers within each routing table bucket on the lookup performance. We propose a new, yet backward-compatible, neighbour selection scheme that attempts to maximize the aforementioned diversity. The scheme does not cause additional overhead except negligible computations for comparing the diversity of identifiers. We present a theoretical model for the actual impact of the new scheme on the lookup's hop count and validate it against simulations of three exemplary Kademlia-type systems. We also measure the performance gain enabled by a partial deployment for the scheme in the real KAD system. The results confirm the superiority of the systems that incorporate our scheme.
    07/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Freenet, a fully decentralized publication system designed for censorship-resistant communication, exhibits long delays and low success rates for finding and retrieving content. In order to improve its perfor- mance, an in-depth understanding of the deployed system is required. Therefore, we performed an extensive measurement study accompanied by a code analysis to identify bottlenecks of the existing algorithms and obtained a realistic user model for the improvement and evaluation of new algorithms. Our results show that 1) the current topology control mechanisms are suboptimal for routing and 2) Freenet is used by several tens of thousands of users who exhibit uncharacteristically long online times in comparison to other P2P systems.
    PETs 2014; 07/2014
  • Benjamin Schiller, Giang Nguyen, Thorsten Strufe
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    ABSTRACT: Using Peer-to-Peer technology to deliver live video streams to mobile devices is a promising approach. It allows service providers to scale their video distribution without increasing their cost. As the resources are replicated at the edge of the network, mobile devices can take advantage of close-by peers in order to get the required data faster. This, however, is challenging due to the highly dynamic nature of the participating mobile devices. Hence, the video distribution overlay needs to adapt quickly to changes in the available bandwidth as well as the location of peers. Also, it should be resilient to arbitrary disconnects as well as targeted attacks. In this paper, we introduce a multi-tree-push streaming system which takes the upload capacities of mobile devices into account and arranges the overlay connections based on their position in the network topology. Our demonstrations show that our system is resilient to churn and attacks while running on desktop machines and mobile devices.
    2014 IEEE International Conference on Pervasive Computing and Communication Workshops (PERCOM WORKSHOPS); 03/2014
  • Source
    Stefanie Roos, Thorsten Strufe
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    ABSTRACT: Social Overlays suffer from high message delivery delays due to insufficient routing strategies. Limiting connections to device pairs that are owned by individuals with a mutual trust relationship in real life, they form topologies restricted to a subgraph of the social network of their users. While centralized, highly successful social networking services entail a complete privacy loss of their users, Social Overlays at higher performance represent an ideal private and censorship-resistant communication substrate for the same purpose. Routing in such restricted topologies is facilitated by embedding the social graph into a metric space. Decentralized routing algorithms have up to date mainly been analyzed under the assumption of a perfect lattice structure. However, currently deployed embedding algorithms for privacy-preserving Social Overlays cannot achieve a sufficiently accurate embedding and hence conventional routing algorithms fail. Developing Social Overlays with acceptable performance hence requires better models and enhanced algorithms, which guarantee convergence in the presence of local optima with regard to the distance to the target. We suggest a model for Social Overlays that includes inaccurate embeddings and arbitrary degree distributions. We further propose NextBestOnce, a routing algorithm that can achieve polylog routing length despite local optima. We provide analytical bounds on the performance of NextBestOnce assuming a scale-free degree distribution, and furthermore show that its performance can be improved by more than a constant factor when including Neighbor-of-Neighbor information in the routing decisions.
    01/2014;
  • Hani Salah, Stefanie Roos, Thorsten Strufe
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    ABSTRACT: Discovery of nodes and content in large-scale distributed systems is generally based on Kademlia, today. Understanding Kademlia-type systems to improve their performance is essential for maintaining a high service quality for an increased number of participants, particularly when those systems are adopted by latency-sensitive applications. This paper contributes to the understanding of Kademlia by studying the impact of diversifying neighbours’ identifiers within each routing table bucket on the lookup performance. We propose a new, yet backward-compatible, neighbour selection scheme that attempts to maximize the aforementioned diversity. The scheme does not cause additional overhead except negligible computations for comparing the diversity of identifiers. We present a theoretical model for the actual impact of the new scheme on the lookup’s hop count and validate it against simulations of three exemplary Kademlia-type systems. We also measure the performance gain enabled by a partial deployment for the scheme in the real KAD system. The results confirm the superiority of the systems that incorporate our scheme.
    IEEE P2P, London; 01/2014
  • Hani Salah, Stefanie Ross, Thorsten STrufe
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    ABSTRACT: The widely used distributed hash table (DHT) in KAD is commonly analyzed and optimized based on partial measurements and simulation results, which are limited in scope and subject to simplification. An accurate characterization, however, is vital for a thorough understanding and effective enhancement. Analyzing and comparing complete real graphs collected from a large-scale measurement campaign as well as synthetic graphs generated by a novel simulation model, we study their degree distributions as well as resilience in face of random departure and targeted attacks. Our results show that the online KAD graph, although scale-free, is highly robust not only to random departure, but also to targeted attacks, making it suitable for distributed applications requiring a high resilience. Resilience to random departure and shape of degree distribution are well modelled by the simulations. However, due to a greatly increased ratio of stale routing information, the complete graph in the real system is much more vulnerable to targeted attacks compared to estimations based on simulative results.
    IEEE ISCC, Madeira, Portugal; 01/2014
  • Hani Salah, Benjamin Schiller, Thorsten Strufe
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    ABSTRACT: Content-Centric Networking (CCN) promises to yield large efficiency gains for Internet content distribution. Its autonomous cache management, however, raises doubts about achieving the intended goals optimally. A coordinated cache management, based on timely usage information, will help to fully leverage the cache efficiency. In this poster we introduce CoMon, a system architecture that implements Coordinated caching based on Monitoring of content usage and its stability. CoMon aims at improving CCN caching with low monitoring and communication overheads.
    IEEE INFOCOM, Toronto, Canada; 01/2014
  • Source
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    ABSTRACT: The design of secure and usable access schemes to personal data represent a major challenge of online social networks (OSNs). State of the art requires prior interaction to grant access. Sharing with users who are not subscribed or previously have not been accepted as contacts in any case is only possible via public posts, which can easily be abused by automatic harvesting for user profiling, targeted spear-phishing, or spamming. Moreover, users are restricted to the access rules defined by the provider, which may be overly restrictive, cumbersome to define, or insufficiently fine-grained. We suggest a complementary approach that can be easily deployed in addition to existing access control schemes, does not require any interaction, and includes even public, unsubscribed users. It exploits the fact that different social circles of a user share different experiences and hence encrypts arbitrary posts. Hence arbitrary posts are encrypted, such that only users with sufficient knowledge about the owner can decrypt. Assembling only well-established cryptographic primitives, we prove that the security of our scheme is determined by the entropy of the required knowledge. We consequently analyze the efficiency of an informed dictionary attack and assess the entropy to be on par with common passwords. A fully functional implementation is used for performance evaluations, and available for download on the Web.
    09/2013;
  • Source
    Stefanie Roos, Hani Salah, Thorsten Strufe
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    ABSTRACT: The family of Kademlia-type systems represents the most efficient and most widely deployed class of internet-scale distributed systems. Its success has caused plenty of large scale measurements and simulation studies, and several improvements have been introduced. Its character of parallel and non-deterministic lookups, however, so far has prevented any concise formal analysis. This paper introduces the first comprehensive formal model of the routing of the entire family of systems that is validated against previous measurements. It sheds light on the overall hop distribution and lookup delays of the different variations of the original protocol. It additionally shows that several of the recent improvements to the protocol in fact have been counter-productive and identifies preferable designs with regard to routing overhead and resilience.
    07/2013;
  • Benjamin Schiller, Thorsten Strufe
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    ABSTRACT: With the rise of online social networks and other highly dynamic system, the need for the analysis of their structural properties has grown in the last years. While the re-computation of graph-theoretic metrics is feasible for investigating a small set of static system snapshots, this approach is unfit for the application in highly dynamic systems where we aim at frequent property updates. Based on the concept of data streams, new algorithms have been developed that update the computed properties based on changes instead of recomputing them regularly. While there exists a plethora of frameworks and libraries for the analysis of static networks, there is currently no framework for the graph-theoretic analysis and development of new algorithms for dynamic networks. In this paper, we discuss a set of requirements a framework must meet to implement the general workflow for analyzing dynamic networks. We then introduce the architecture of a first prototype for such a framework, the Dynamic Network Analyzer (DNA).
    Proceedings of the 2013 Summer Computer Simulation Conference; 07/2013
  • Benjamin Schiller, Thorsten Strufe
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    ABSTRACT: Routing in complex networks is increasingly optimized towards situation and properties of the underlying network. Quick hypothesis testing with respect to the performance of different strategies, however, is posing to be an unnecessarily complicated task. To this end we propose GTNA-2, the enhanced second version of Graph-Theoretic Network Analyzer. Based on the broadly used GTNA, it allows both for the efficient and simple analysis of a large set of graph metrics, but additionally has been extended with support for rapid prototyping and quick evaluation of arbitrary routing algorithms. In this paper, we discuss the implementation and evaluation of routing algorithms in GTNA-2. As a proof of concept, we demonstrate the framework's ease of use by comparing the routing performance of Named data Networking with basic IP-based routing.
    Proceedings of the 2013 Summer Computer Simulation Conference; 07/2013
  • Giang Nguyen, Mathias Fischer, Thorsten Strufe
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    ABSTRACT: Overlay streaming systems have recently been favored by the academic community as a viable approach for IPTV. Over the last years, a multitude of different overlay streaming approaches have been proposed. Most of them, however, have been evaluated individually. The lack of a common simulation framework makes it difficult to compare the properties of the different systems with each other. To bridge this gap, we introduce OSSim, a general-purpose simulation framework that allows the instantiation of different overlay streaming protocols. For this purpose, it provides a generic and modular structure, and several membership management and overlay streaming protocols as well. Our simulation results indicate that the framework is accurate and flexible to simulate different overlay streaming systems.
    In Proceedings of Summer Simulation Multi-Conference (SummerSim). 07/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Our main contribution in this work is a deployable multitree-push system for P2P-based live streaming. It runs on both desktop PCs and Android-based mobile devices. Additionally, it provides controlling, monitoring, and measurement functionalities which help with debugging in the development phase, visualize the topology during a demonstration, and support the deployment of test scenarios in a distributed setting. Besides, the generic architecture of the system also allows for the extension to other classes of streaming systems.
    Peer-to-Peer Computing (P2P), 2013 IEEE Thirteenth International Conference on; 01/2013
  • Conference Paper: Summary and conclusion
    Wolfgang Effelsberg, Thorsten Strufe
    Benchmarking Peer-to-Peer Systems; 01/2013
  • S. Roos, T. Strufe
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    ABSTRACT: Routing in Darknets, membership concealing overlays for pseudonymous communication, like for instance Freenet, is insufficiently analyzed, barely understood, and highly inefficient. These systems at higher performance are promising privacy preserving solutions for social applications. This paper contributes a realistic analytical model and a novel routing algorithm with provable polylog expected routing length. Using the model, we additionally prove that this can not be achieved by Freenet's routing. Simulations support that our proposed algorithm achieves a better performance than Freenet for realistic network sizes.
    INFOCOM, 2013 Proceedings IEEE; 01/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: Motivated by the popularity of content distribution and file sharing applications that nowadays dominate Internet traffic, we focus on the incentive mechanism of a very popular, yet not very well studied, peer-to-peer application, eMule. In our work, we recognize that the incentive scheme of eMule is more sophisticated than current alternatives (e.g., BitTorrent) as it uses a general, priority-based, time-dependent queuing discipline to differentiate service among cooperative users and free-riders. In this paper, we describe a general model of such an incentive mechanism and analyze its properties in terms of application performance. We validate our model using both numerical simulations (when analytical techniques become prohibitive) and with a measurement campaign of the live eMule system. Our results, in addition to validating our model, indicate that the incentive scheme of eMule suffers from starvation. Therefore, we present an alternative scheme that mitigates this problem, and validate it through numerical simulations and a second measurement campaign.
    IEEE Journal on Selected Areas in Communications 01/2013; 31(9):94-104. · 3.12 Impact Factor
  • H. Salah, T. Strufe
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    ABSTRACT: Measuring accurate graph snapshots of peer-to-peer (P2P) overlay networks is essential to understand these systems. Furthermore, the captured graph snapshots can be used, among other important purposes, as traces for simulation studies, to validate existing simulation models, to design and implement targeted attacks, or to detect anomalies. Motivated by the importance of the purposes above as well as the popularity of several Kademlia-like networks, we present a new crawler aiming to capture snapshots of the connectivity graph of the entire KAD network. The crawler's design is generic and adaptable for Kademlia-like and other structured P2P networks. The results show that the crawler is fast and captures high accurate graph snapshots. Furthermore, its design enables it to outperform prior KAD crawlers significantly in terms of the time and the number of crawling messages that are required to download nodes' routing tables. The crawls that we conducted at different times between April 2012 and February 2013 show that KAD is still widely-used in terms of total observed users. However, when compared to the results of prior studies, we report a significant drop in the number of its simultaneous online users.
    Distributed Computing Systems Workshops (ICDCSW), 2013 IEEE 33rd International Conference on; 01/2013

Publication Stats

365 Citations
11.00 Total Impact Points

Institutions

  • 2010–2013
    • Technical University Darmstadt
      • • Telecooperation Lab (TK)
      • • Multimedia Communications Lab (KOM)
      Darmstadt, Hesse, Germany
  • 2012
    • Northeastern University
      Boston, Massachusetts, United States
  • 2010–2011
    • Universität Mannheim
      Mannheim, Baden-Württemberg, Germany
  • 2009
    • University of Nice-Sophia Antipolis
      Nice, Provence-Alpes-Côte d'Azur, France
    • Institut de France
      Lutetia Parisorum, Île-de-France, France
  • 2003–2007
    • Technische Universität Ilmenau
      Stadt Ilmenau, Thuringia, Germany