Traffic microstructures and network anomaly detection

Much hope has been put in the modelling of network traffic with machine learning methods to detect previously unseen attacks. Many methods rely on features on a microscopic level such as packet sizes or interarrival times to identify reoccurring patterns and detect deviations from them. However, the success of these methods depends both on the quality of corresponding training and evaluation data as well as the understanding of the structures that methods learn. Currently, the academic community is lacking both, with widely used synthetic datasets facing serious problems and the disconnect between methods and data being named the "semantic gap". This thesis provides extensive examinations of the necessary requirements on traffic generation and microscopic traffic structures to enable the effective training and improvement of anomaly detection models. We first present and examine DetGen, a container-based traffic generation paradigm that enables precise control and ground truth information over factors that shape traffic microstructures. The goal of DetGen is to provide researchers with extensive ground truth information and enable the generation of customisable datasets that provide realistic structural diversity. DetGen was designed according to four specific traffic requirements that dataset generation needs to fulfil to enable machine-learning models to learn accurate and generalisable traffic representations. Current network intrusion datasets fail to meet these requirements, which we believe is one of the reasons for the lacking success of anomaly-based detection methods. We demonstrate the significance of these requirements experimentally by examining how model performance decreases when these requirements are not met. We then focus on the control and information over traffic microstructures that DetGen provides, and the corresponding benefits when examining and improving model failures for overall model development. We use three metrics to demonstrate that DetGen is able to provide more control and isolation over the generated traffic. The ground truth information DetGen provides enables us to probe two state-of-the-art traffic classifiers for failures on certain traffic structures, and the corresponding fixes in the model design almost halve the number of misclassifications . Drawing on these results, we propose CBAM, an anomaly detection model that detects network access attacks through deviations from reoccurring flow sequence patterns. CBAM is inspired by the design of self-supervised language models, and improves the AUC of current state-of-the-art by up to 140%. By understanding why several flow sequence structures present difficulties to our model, we make targeted design decisions that improve on these difficulties and ultimately boost the performance of our model. Lastly, we examine how the control and adversarial perturbation of traffic microstructures can be used by an attacker to evade detection. We show that in a stepping-stone attack, an attacker can evade every current detection model by mimicking the patterns observed in streaming services

Low-frequency gravitational-wave science with eLISA/NGO

We review the expected science performance of the New Gravitational-Wave Observatory (NGO, a.k.a. eLISA), a mission under study by the European Space Agency for launch in the early 2020s. eLISA will survey the low-frequency gravitational-wave sky (from 0.1 mHz to 1 Hz), detecting and characterizing a broad variety of systems and events throughout the Universe, including the coalescences of massive black holes brought together by galaxy mergers; the inspirals of stellar-mass black holes and compact stars into central galactic black holes; several millions of ultracompact binaries, both detached and mass transferring, in the Galaxy; and possibly unforeseen sources such as the relic gravitational-wave radiation from the early Universe. eLISA's high signal-to-noise measurements will provide new insight into the structure and history of the Universe, and they will test general relativity in its strong-field dynamical regime.Comment: 20 pages, 8 figures, proceedings of the 9th Amaldi Conference on Gravitational Waves. Final journal version. For a longer exposition of the eLISA science case, see http://arxiv.org/abs/1201.362

Functional Autonomy Techniques for Manipulation in Uncertain Environments

As robotic platforms are put to work in an ever more diverse array of environments, their ability to deploy visuomotor capabilities without supervision is complicated by the potential for unforeseen operating conditions. This is a particular challenge within the domain of manipulation, where significant geometric, semantic, and kinetic understanding across the space of possible manipulands is necessary to allow effective interaction. To facilitate adoption of robotic platforms in such environments, this work investigates the application of functional, or behavior level, autonomy to the task of manipulation in uncertain environments. Three functional autonomy techniques are presented to address subproblems within the domain. The task of reactive selection between a set of actions that incur a probabilistic cost to advance the same goal metric in the presence of an operator action preference is formulated as the Obedient Multi-Armed Bandit (OMAB) problem, under the purview of Reinforcement Learning. A policy for the problem is presented and evaluated against a novel performance metric, disappointment (analogous to prototypical MAB's regret), in comparison to adaptations of existing MAB policies. This is posed for both stationary and non-stationary cost distributions, within the context of two example planetary exploration applications of multi-modal mobility, and surface excavation. Second, a computational model that derives semantic meaning from the outcome of manipulation tasks is developed, which leverages physics simulation and clustering to learn symbolic failure modes. A deep network extracts visual signatures for each mode that may then guide failure recovery. The model is demonstrated through application to the archetypal manipulation task of placing objects into a container, as well as stacking of cuboids, and evaluated against both synthetic verification sets and real depth images. Third, an approach is presented for visual estimation of the minimum magnitude grasping wrench necessary to extract massive objects from an unstructured pile, subject to a given end effector's grasping limits, that is formulated for each object as a "wrench space stiction manifold". Properties are estimated from segmented RGBD point clouds, and a geometric adjacency graph used to infer incident wrenches upon each object, allowing candidate extraction object/force-vector pairs to be selected from the pile that are likely to be within the system's capability.</p

Applications of nonlinear approximation for problems in learning theory and applied mathematics

A major pillar of approximation theory in establishing the ability of one class of functions to be represented by another. Establishing such a relationship often leads to efficient numerical approximation methods. In this work, several expressibility theorems are established and several novel numerical approximation techniques are also presented. Not only are these novel methods supported by the presented theory, but also, provided numerical experiments show that these novel methods may be applied to a wide range of applications from image compression to the solutions of high-dimensional PDE