Volume 36, Issue 1

Abstract: This paper is a summary of the main contributions of the PhD thesis published in [1]. The main research contributions of the thesis are driven by the research question how to design simple, yet efficient and robust run-time adaptive resource allocation schemes within the communication stack of Wireless Sensor Network (WSN) nodes. The thesis addresses several problem domains with contributions on different layers of the WSN communication stack. The main contributions can be summarized as follows: First, a a novel run-time adaptive MAC protocol is introduced, which stepwise allocates the power-hungry radio interface in an on-demand manner when the encountered traffic load requires it. Second, the thesis outlines a methodology for robust, reliable and accurate software-based energy-estimation, which is calculated at network runtime on the sensor node itself. Third, the thesis evaluates several Forward Error Correction (FEC) strategies to adaptively allocate the correctional power of Error Correcting Codes (ECCs) to cope with timely and spatially variable bit error rates. Fourth, in the context of TCP-based communications in WSNs, the thesis evaluates distributed caching and local retransmission strategies to overcome the performance degrading effects of packet corruption and transmission failures when transmitting data over multiple hops. The performance of all developed protocols are evaluated on a self-developed real-world WSN testbed and achieve superior performance over selected existing approaches, especially where traffic load and channel conditions are suspect to rapid variations over time.

Abstract: Kooperative Netze beruhen auf dem Prinzip der Zusammenarbeit von Benutzern auf Netzwerkebene. Sie ermöglichen dabei Kommunikation, wo andere Netzformen an wirtschaftliche oder technische Grenzen stoßen. Beispiele für kooperative Netzwerke sind dezentrale drahtlose Mesh-Netzwerke, Wi-Fi-Communities oder hybride Formen dieser Netzwerk-Typen. In kooperativen Netzen übernehmen Benutzergeräte Kernfunktionen des Netzes, wie z. B. die Weiterleitung von Paketen. Diese Kooperation bedingt eine opportunistische Offenheit, welche zu neuen Sicherheitsrisiken führt. Besonders die fehlende Möglichkeit zur Authentifizierung von Datenverkehr durch die weiterleitenden Geräte macht sie anfällig für Angriffe. Diese Arbeit schafft die Grundlagen für eine hocheffiziente Authentifizierung von Netzwerkverkehr durch die Knoten im Netzwerk. Dies erlaubt es, die Identität eines Senders und die Integrität seiner Nachrichten effizient zu überprüfen, bevor die Nachrichten weitergeleitet werden. So können unauthentifizierte Datenströme und Angriffe effizient unterbunden werden.

Zusammenfassung: Die aktuelle Beliebtheit von sozialen Netzwerken im Internet deutet auf das allgemeine Interesse an sozial-bewussten, nutzerorientierten Kommunikationsapplikationen hin. Gleichzeitig werden mobile Nutzergeräte sowohl mächtiger als auch weiter verbreitet. User-Centric Networking (UCN) ist eine Implikation dieser Tendenzen – die Realisierung von nutzerorientierten Kommunikationsapplikationen und -diensten direkt durch Nutzergeräte, also unabhängig von einer Server-basierten Infrastruktur. In diesem Beitrag wird ein neuartiges, vollständig dezentrales Overlay vorgestellt, das die Entwicklung von komplexen UCN-Applikationen ermöglicht. Im Gegenzug zu klassischen Overlay-Entwürfen nutzt der vorgestellte Ansatz den sozialen Kontext zwischen Nutzern, um eine bessere Vermaschung zwischen Geräten von befreundeten Nutzern zu erreichen. Das Overlay realisiert eine hohe Lokalität des Datenverkehrs zwischen Nutzern und unterstützt die zeitversetzte Zustellung von Nachrichten an Geräte, die zum Zeitpunkt des Sendens nicht verfügbar waren. Simulationen zeigen, dass der vorgestellte Ansatz nahezu optimale Latenzen erreicht und gut mit wachsenden Netzwerkgrößen skaliert.

Abstract: Today, lightweight IP stacks enable highly constrained devices like smart objects to exchange information with each other as well as with backend services over the Internet. To protect the confidentiality and integrity of data that is gathered by smart objects, e.g., in industrial monitoring or e-health systems, the communicating peers need to authenticate each other and encrypt the transmitted data. Security protocols thereby must handle the constrained resources of smart objects that only offer a few KB of RAM and ROM, are equipped with CPUs of a few MHz and often are battery-powered. In this article, we provide a brief overview and analysis of the IP security protocols DTLS, Minimal IKE, and HIP DEX that are currently in focus of standardization efforts. We then present our optimization for the HIP DEX DoS protection mechanism and hint at further improvements that are discussed in the work this article is based on. Finally, we provide a detailed overhead evaluation of the HIP DEX protocol based on our own implementation for smart objects.

Abstract: One- and two-dimensional barcodes have become very popular in past years and are widely used to identify products as well as services. Recently, 2D barcodes, likeQRcodes, are also used to optically transfer a dedicated hyperlink. All 2D barcodes share one major limitation: the storage capacity. To overcome that, time can be introduced as a third dimension. Instead of one, a sequence of barcodes is used to transfer a larger amount of data. The main goal of the present work was to design, implement, and especially evaluate the entire workflow for such a QR codebased, three-dimensional (3D) transmission system on the receiver side, such as a SmartPhone, being able to “read” from a sender, represented by a screen. The steps comprise the capturing of the 3D barcode, the recognition and reading of the sequence of 2D barcodes, and the final retrieval of the original content. Furthermore, adversarial conditions had to be identified, tested, and documented in detail. The prototype achieves a theoretical throughput of 12,288 Byte for 30 seconds transmission intervals, which results in approximately 3,280 bit/s. Future work may focus on increasing the throughput of the system as well as the transmission reliability by applying error detection and correction techniques.

Abstract: Following the Everything-as-a-Service paradigm, digital and physical assets such as software, data and hardware resources can be offered and delivered as services by their respective owners. The rise of service-oriented personal cloud computing requires new techniques for users to perform asset discovery, exchange and management. These techniques must be easy to use and yet powerful enough to result in largescale distributed systems over federated personal clouds. With CloudRemix, an interactive cockpit to manage personal clouds and their federations, we achieve a reduced reliance on central infrastructures and a raised balance of service provisioning and consumption. Attached to a novel local device discovery tool named FlexiSource, to a service registry and to a social network, the CloudRemix prototype demonstrates its utility to manage personal clouds in both social and market-driven environments.

Abstract: Pervasive Social Computing (PSC) is an ongoing research trend of merging the two worlds of pervasive computing and social computing. While there are already lots of promising PSC applications, building such systems is still very sophisticated and error-prone. The Mobilis framework provides developer support for mobile pervasive apps (native Android and HTML5), a service environment for dynamic deployment of services, authentication and robust communication over unreliable networks as well asanemulation environment to be able to mimick user behavior and to test applications in a lab environment before field tests. The system is available as open source software on Github.

Abstract: Traffic Classification is a hot topic in many different contexts, such as management of enterprise networks, and scientific research on the Internet and on aspects related to network neutrality and censorship. Despite the large quantity of works published in the past few years on traffic classification, aside from port-based classifiers and those based on payload inspection (having well-known issues related to privacy of users and computational cost), there are few implementations made available to the community – for experimenting – and to Telecom Operators – for controlling their networks – that target alternative and novel approaches for traffic classification. In order to experiment with new algorithms and approaches and to correctly operate real networks, there is a strong need for open platforms.

Abstract: Approaches and systems for network workload generation are useful and effective only when they produce network traffic that is realistic and representative as much as possible of the real workload of the network scenario under study. Distributed Internet Traffic Generator (D-ITG) [1] is a platform capable to produce IPv4 and IPv6 traffic by accurately replicating the workload of current Internet applications. Two main alternative approaches exist in literature for the generation of such workload: (a) trace-based generation (TCPReplay, TCPivo, TCPopera, etc.), in which flows exactly replicate the content and the timings of traffic traces previously collected in real scenarios; (b) analytical model-based generation (TG, MGEN, RUDE/CRUDE, D-ITG, etc.), in which flow and packet generation processes are based on statistical models. With D-ITG, the generation can follow (i) simple stochastic models for packet size (PS) and inter departure time (IDT), (ii) more complex analytical models that mimic application-level protocol behavior, (iii) real traffic patterns captured in traffic traces.

Abstract: The increasing popularity of Cloud Computing is leading to the emergence of large virtualized data centers hosting increasingly complex and dynamic IT systems and services. Over the past decade, the efficient sharing of computational resources through virtualization has been subject to intensive research, while network management in cloud data centers has received less attention. A variety of network-intensive applications require QoS (Quality-of-Service) provisioning, performance isolation and support for flexible and efficient migration of virtual machines. In this paper, we survey existing network virtualization approaches and evaluate the extent to which they can be used as a basis for realizing the mentioned requirements in a cloud data center. More specifically, we identify generic network virtualization techniques, characterize them according to their features related to QoS management and performance isolation, and show how they can be composed together and used as building blocks for complex network virtualization solutions. We then present an overview of selected representative cloud platforms and show how they leverage the generic techniques as a basis for network resource management. Finally, we outline open issues and research challenges in the area of performance modeling and proactive resource management of virtualized data center infrastructures.

Abstract: Die Deutsche Forschungsgemeinschaft (DFG) hat der Technischen Universität Darmstadt einen weiteren Sonderforschungsbereich (SFB) bewilligt. „MAKI – Multi- Mechanismen-Adaption für das künftige Internet“ ist das Thema des neu eingerichteten SFB 1053, der ab Januar 2013 startet und für zunächst vier Jahre mit insgesamt etwa 8 Millionen Euro gefördert wird. Darüber hinaus sind die RWTH Aachen und die University of Illinois at Urbana- Champain an dem SFB beteiligt.

Abstract: Das Institut für BWL und Wirtschaftsinformatik unter der Leitung von Univ. Prof. Dr. Sarah Spiekermann möchte durch Einsatz eines breiten Methodenspektrums eine „nachhaltige“ Techniklandschaft mitgestalten. Der inhaltliche Schwerpunkt liegt dabei auf Fragen zum Erhalt von Privatsphäre und Kontrolle in allgegenwärtigen elektronischen und insbesondere kontextadaptiven Umgebungen.