Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Pattern Recognition and Machine Learning

Wireless sensor network applications, similarly to other distributed systems, often require a scalable time synchronization service enabling data consistency and coordination. This paper describes the Flooding Time Synchronization Protocol (FTSP), especially tailored for applications requiring stringent precision on resource limited wireless platforms. The proposed time synchronization protocol uses low communication bandwidth and it is robust against node and link failures. The FTSP achieves its robustness by utilizing periodic flooding of synchronization messages, and implicit dynamic topology update. The unique high precision performance is reached by utilizing MAC-layer time-stamping and comprehensive error compensation including clock skew estimation. The sources of delays and uncertainties in message transmission are analyzed in detail and techniques are presented to mitigate their effects. The FTSP was implemented on the Berkeley Mica2 platform and evaluated in a 60-node, multi-hop setup. The average per-hop synchronization error was in the one microsecond range, which is markedly better than that of the existing RBS and TPSN algorithms.

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The flooding time synchronization protocol

As more software modules and external interfaces are getting added on vehicles, new attacks and vulnerabilities are emerging. Researchers have demonstrated how to compromise in-vehicle Electronic Control Units (ECUs) and control the vehicle maneuver. To counter these vulnerabilities, various types of defense mechanisms have been proposed, but they have not been able to meet the need of strong protection for safety-critical ECUs against in-vehicle network attacks. To mitigate this deficiency, we propose an anomaly-based intrusion detection system (IDS), called Clock-based IDS (CIDS). It measures and then exploits the intervals of periodic in-vehicle messages for fingerprinting ECUs. The thus-derived fingerprints are then used for constructing a baseline of ECUs' clock behaviors with the Recursive Least Squares (RLS) algorithm. Based on this baseline, CIDS uses Cumulative Sum (CUSUM) to detect any abnormal shifts in the identification errors - a clear sign of intrusion. This allows quick identification of in-vehicle network intrusions with a low false-positive rate of 0.055%. Unlike state-of-the-art IDSs, if an attack is detected, CIDS's fingerprinting of ECUs also facilitates a rootcause analysis; identifying which ECU mounted the attack. Our experiments on a CAN bus prototype and on real vehicles have shown CIDS to be able to detect a wide range of in-vehicle network attacks.

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Fingerprinting electronic control units for vehicle intrusion detection

Distributed time synchronization is an important part of a sensor network where sensing and actuation must be coordinated across multiple nodes. Several time synchronization protocol that maximize accuracy and energy conservation have been developed, including FTSP, TPSN, and RBS. All of these assume nearly instantaneous wireless communication between sensor nodes; each of them work well in today's RF-based sensor networks. We are just beginning to explore underwater sensor networks where communication is primarily via acoustic telemetry. With acoustic communication, where the propagation speed is nearly five orders of magnitude slower than RF, assumptions about rapid communication are incorrect and new approaches to time synchronization are required. We present Time Synchronization for High Latency (TSHL), designed as- suming such high latency propagation. We show through analysis and simulation that it achieves precise time synchronization with minimal energy cost. Although at very short distances existing protocols are adequate, TSHL shows twice the accuracy at 500m, demonstrating the need to model both clock skew and propagation latency.

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Time Synchronization for High Latency Acoustic Networks

Distributed architectures for industrial applications are a new opportunity to realize cost-effective, flexible, scalable and reliable systems. Direct interfacing of sensors and actuators to the industrial communication network improves the system performance, because process data and diagnostics can be simultaneously available to many systems and also shared on the Web. However, sensors, especially low-cost ones, cannot use standard communication protocols suitable for computers and PLCs. In fact, sensors typically require a cyclic, isochronous and hard real-time exchange of few data, whereas PCs and PLCs exchange a large amount of data with soft real-time constrains. Looking at the industrial communication systems, this separation is clearly visible: several fieldbuses have been designed for specific sensor application areas, whereas high-level industrial equipments use wired/wireless Ethernet and Internet technologies. Recently, traditional fieldbuses were replaced by Real-Time Ethernet protocols, which are ''extended'' versions of Ethernet that meet real-time operation requirements. Besides, real-time wireless sensor networking seems promising, as demonstrated by the growing research activities. In this paper, an overview of the state-of-art of real-time sensor networks for industrial applications is presented. Particular attention has been paid to the description of methods and instrumentation for performance measurement in this kind of architectures.

Wired and wireless sensor networks for industrial applications

The introduction of computer-controlled intelligent safety and comfort features has turned cars into complex distributed computing systems. In such a system the proper operation of the communication backbone as well as the proper interaction of components from different vendors must be ensured for all configurations and operating conditions. This system-level test goes far beyond the (isolated) test of single components and represents a substantial problem, that seems to be still largely unsolved, although its solution is crucial for maintaining the consumers' trust in modern automotive electronics. In this paper we concentrate on the test of distributed systems based on FlexRay, the protocol that is envisioned as the communication backbone for future automotive systems. The cornerstones of our approach are a decomposition of the system into layers and mechanisms, and a versatile strategy for monitoring and stimulation under various conditions. Our concept can be adapted to diverse needs ranging from an early debugging with full access to the system, over non-intrusive online testing during interoperability tests, to maintenance testing that is restricted to a remote access only. We give detailed discussions of the requirements and present our solutions for the various issues involved. Selected use cases demonstrate the usefulness of the taken approach.

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Towards a Systematic Test for Embedded Automotive Communication Systems

High-accuracy external clock synchronization can only be achieved with adequate hardware support. We analyze the requirements and present the specification and implementation of an ASIC running under the acronym UTCSU dedicated to that purpose. It is built around an elaborated local clock, which is based on an adder driven by a fixed-frequency oscillator. This novel clock design allows a fine grained rate adjustability apt for maintaining both local time with linear continuous amortization and accuracy information as needed in interval-based clock synchronization. Additional features incorporated in our UTCSU are facilities to timestamp clock synchronization data packets, interfaces to couple GPS receivers, some application support as well as sophisticated self-test machinery. Apart from addressing design and engineering issues of the chip, we also provide a basic programming model.

Specification and Implementation of the Universal TimeCoordinated Synchronization Unit (UTCSU)

This article presents an overview and some evaluation results of our PSynUTC 1 prototype system for GPS time distribution and time synchronization in Ethernetbased LANs. PSynUTC does not need dedicated GPS receivers at every computing node but uses ordinary data packets for disseminating time information. High accuracy is achieved by combining (1) hardware packet timestamping at the network interface of nodes and switches, (2) high-resolution, high-frequency adder-based clocks with superior adjustment capabilities, and (3) clock rate synchronization algorithms compensating typical TCXO drifts. Our technology can be employed with any network controller chipset that supports the media-independent interface (MII) standard. Moreover, standard device drivers and protocol stacks can be used without any change. Our evaluation results show that PSynUTC will achieve a worst case synchronization accuracy in the 100 ns range, which is an improvement of at least 4 orders of magnitude over conventional software-based approaches like NTP.

PSynUTC - Evaluation of a High Precision Time Synchronization Prototype System for Ethernet LANs

: This paper shows how to distribute GPS-time with micro-accuracy and below even in Ethernet-based distributed systems. Our SynUTC-approach is based upon a simple network controller-level hardware for timestamping data packets as they leave and arrive at a node, which comes in two flavors: The memory-based times-tamping method exploited by our Network Time Interface (NTI) M-Module timestamps data packets as the network controller accesses them in memory. This technique can be used for virtually any type of network and network controllers. For 10 Mb/s Ethernet, for example, our experimental evaluation revealed a time distribution accuracy down to the pus-range.

How to Distribute GPS-Time Over COTS-Based LANs

This paper provides a description of our Network Time Interface M-Module (NTI) supporting high-accuracy external clock synchronization by hardware. The NTI is built around our custom Universal Time Coordinated Synchronization Unit VLSI chip (UTCSU-ASIC), which contains most of the hardware support required for interval-based clock synchronization: A state and rate adjustable clock device with a high resolution, automatically maintained accuracy intervals, interfaces to GPS receivers, and various timestamping features. Designed for maximum network controller and CPU independence, our NTI provides a turn-key solution for adding synchronized clocks to distributed real-tune systems built upon hardware with M-Module interfaces.

Martin Horauer

Papers

Towards a Systematic Test for Embedded Automotive Communication Systems

Specification and Implementation of the Universal TimeCoordinated Synchronization Unit (UTCSU)

PSynUTC - Evaluation of a High Precision Time Synchronization Prototype System for Ethernet LANs

How to Distribute GPS-Time Over COTS-Based LANs

NTI: A Network Time Interface M-module for high-accuracy clock synchronization