Multi-Level Hybrid Flying Capacitor (MLHFC) converters are emerging high energy density dc-dc converters. This paper presents an online feedback stability region detection and flying capacitor (FC) balancing technique for MLHFC converters. The feedback region detector monitors the FC voltage and the internal control signal of the FC control loop to detect the feedback region and adapt the controller accordingly. The proposed detector is control type independent and can be embedded e.g. in a digital Sliding Mode Controller (SMC). In this work, the feedback detection mechanism directly acts inside the controller to balance the FC voltage. The analyzed controller offers a wide range of possible applications, resulting in a very versatile controller for MLHFC converters. Simulation results highlight the effectiveness and robustness of the proposed control architecture.

This paper presents a fully monolithic 3-Level Hybrid Flying Capacitor (3LHFC) converter based on a 130 nm technology node. The design targets a 28V-to-3.3V, 2 A, step-down dc-dc converter. An analog phase-shift modulator keeps the flying capacitor under control, and a dedicated startup circuit brings the flying capacitor to its target value in cold-start conditions. Integration of the full power stage on chip operating at 1 MHz switching frequency results in high conversion efficiency and in the reduction of the external passive components. The presented 3LHFC converter has been validated in silicon. Experimental results are shown and compared with the current state of the art.

In this paper, a digital implementation of a unified sliding mode controller for DC-DC converters is presented. Although current information is used as a control variable, a pure voltage-mode implementation has been considered and the inductor current ripple is digitally reconstructed. The proposed universal control algorithm can be applied to different converter topologies and operating modes. In particular, experimental results are shown for a prototyping system of a Buck converter operating in Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM), where only negligible transient effects are present when changing the operation mode. The presented measurements confirm that the proposed universal control algorithm is capable of achieving tight voltage regulation and excellent dynamic performance under different operating conditions. Additionally, a comparison to a state-of-the-art digital Proportional-Integral-Derivative (PID) controller illustrates the performance improvement of the proposed digital control scheme.

The representation of Internet traffic as connection graphs augments anomaly detection systems by providing insight on the structural connection properties, i.e., who-talks-to-whom. However, these graphs are extremely large and one has to decide in advance on which aspect to focus. In the context of malware detection, this is difficult as malware often mimics legitimate traffic. In this paper, we present a statistical approach for extracting the typical traffic destinations for a set of monitored hosts, and derive a reduced graph that contains only connections that are anomalous for that host. This graph can then be analyzed efficiently. Our system is designed to scale to thousands of monitored hosts. We evaluate our approach using a data set from a real network, and show that we can reliably detect injected malware activity.

More and more Internet services are hosted by Content Distribution Networks or Cloud operators. Often, IP addresses are reused for several services, and the mapping between domain names and IPs has become highly agile. This complicates the analysis of monitoring data, as it is not clear anymore which IP address represents which service at which time. We propose a system that continuously monitors this activity using captured DNS packets in a large network. Thereby we are able to (i) understand the allocation strategies inside a hosting provider, and (ii) report significant changes that are not due the normal agility of a particular service. We evaluate our system using a 2-weeks data set from a large network operator, and demonstrate how it can be used to find malicious sites.

In this paper we review state-of-the-art botnet detection algorithms that reveal the control traffic of malicious peer-topeer (P2P) networks by targeting topological properties of their interconnectivity graph. This class of detection methods does not rely on the exchanged content and therefore is also applicable to encrypted control traffic. However, in practice, an ISP monitoring customer traffic over an edge router will usually see only a fraction of the overall botnet, thus restricting the available bot connectivity information and limiting the applicability of general community detection approaches. In this paper we critically review graph based detection methods suitable for edge router monitoring using two types of real network traces. We show experimentally that using meta-graphs of mutual contacts proposed by Coskun et al. 2010 has the highest potential on result quality. We improve this approach by presenting a computationally less complex algorithm with similar result quality. Furthermore we explain ways to alleviate the cost of dealing with false positives in the result set.

Collaboration of defensive network components of multiple operators is a promising approach for increasing anomaly detection accuracy. This concept involves sharing of possibly sensitive data, hence privacy preservation has to be taken into account. In this paper, we argue that common approaches for sharing traffic information often impede proper analysis due to privacy-preserving mangling operations, and ignore the opportunity to exploit additional knowledge of the originating network operator for interpreting the monitored data. We propose COMINDIS, a lightweight framework for sharing notions of suspiciousness among network operators, and show how to exploit different detection systems for deriving a better understanding of Internet hosts' activities. We evaluate the system both by using a network emulator and by experimenting with a real traffic trace.

Abstract In this paper, we discuss the security threats of next‐generation telecommunication core networks induced by the adoption of Internet technology. The 3GPP IP multimedia subsystem (IMS) is based on the Internet protocol (IP) and hence inherits many security problems from the Internet world. We provide a review of the most prominent vulnerabilities, covering both fundamental functions like routing and name resolution as well as message tampering and implementation attacks, and we show their impact on the IMS. Further, we address the topics of denial of service (DoS) attacks and unsolicited communication (UC). Despite the large number of security threats, the IMS standardization foresees no security monitoring and fully relies on standard countermeasures as known from the Internet. This paper provides a survey of these threats and relates them to the available solutions. We motivate the need for a powerful and modular monitoring platform for the IMS and provide an overview of the existing work in this research field. Copyright © 2009 John Wiley & Sons, Ltd.

SPIT is an upcoming threat for receiving unsolicited messages in Voice over IP systems. We assume, that future SPIT will be sent through the same infrastructure as SPAM today, namely through a network of compromised hosts. Therefore spammers will see SPIT as an additional business case. In this paper we show a viable way to increase the hit rate of a SPIT detection system. Our proposal is to query e-mail SPAM blacklists for IP addresses which are sent with SIP/SDP messages. We enabled a well-established e-mail filter application to handle information out of these messages. We also present the performance of such a solution with respect to call setup delays and success rates.

This article gives a brief overview of our Open Source software framework for generating MPEG-2 Transport Streams carrying digital TV programs and related metadata. Due to the framework's modular architecture and its support for a large variety of broadcast standards, it enables the realization of a broad spectrum of prototype implementations and test setups in the context of Multimedia research and development. We describe three different example configurations for the generation of DVB-T and DVB-H streams that also support MHP applications for local interactivity.