Alexandru Caracas

Mote Runner: A Multi-language Virtual Machine for Small Embedded Devices

This paper introduces a new virtual machine for sensor networks and small embedded devices which has been designed with efficient resource usage and an event-driven programming model in mind. The virtual machine runs on 8, 16, and 32-bit micro-controllers with as little as 4KBof volatile and 32 KB of non-volatile memory. Our virtual machine is not bound to a single high-level programming language, but targets all strictly-typed programming languages.In conjunction with the virtual machine, we also present our development tool chain for Java and C#, and discuss the effects of our virtual machine design on these high-level languages. We also present a compact load-file format which allows applications to be stream-linked in a way that minimizes memory usage and bandwidth. All presented components are part of the IBM Mote Runner, a run-time environment for wireless sensor networks.

A pricing information service for grid computing

This paper addresses two shortcomings that exist in the area of pricing Grid services in an economic Grid environment. The first shortcoming is that there are no standards for pricing schemes, caused by a large difference in the units that are traded (e.g. CPU cycles or virtual clusters) in Grid computing. The second shortcoming is the lack of a model for managing the pricing of informational elements (e.g. software applications) and computational elements (e.g. virtual machines, which comprise resources such as CPU, memory, disk space, network bandwidth). This paper presents a pricing service for Grid computing services, which resolves the shortcomings by introducing a general pricing scheme for informational and computational elements. We describe the functional requirements, architecture, and the interfaces of the pricing service. The pricing service allows expressing the proposed general pricing scheme as an XML document, which can be linked to service level agreements. Contrary to other proposals on pricing, the pricing service is separated from the functionality of metering, accounting, and payment. To validate the concept of a pricing information service, we portray two Utility Computing scenarios.

Mining semantic relations using NetFlow

Knowing the dependencies among computing assets and services provides insights into the computing and business landscape, therefore, facilitating low-risk timely changes in support of a business-driven IT management. In general, the results of a dependency analysis can be used for infrastructure reengineering, show evidence of policy and process compliance, and support assessments of business resilience. Current passive discovery approaches using network monitoring analyze only direct communication between assets and provide just a single- link mesh view. This work introduces a new algorithm based on NetFlow data preprocessed by the Aurora system developed at IBM Research to create a dependency model of the network. The algorithm uses time-based event correlation and the data mining concept of association rules to detect and classify dependencies that span two or more components. The advantages of the algorithm is that no access credentials are required and no packet payload inspection is performed. The suggested algorithm populates and maintains a dependency model of an observed network that describes dependencies among computer systems, software components, and services. The model combines the mined association rules that express relations between flows into dependencies, which are given intuitive semantics. Tests with simulated and authentic data prove the accuracy of the dependency mining algorithm.

On the Expressiveness of BPMN for Modeling Wireless Sensor Networks Applications

Business processes describe the transformations which add economic value to products and services. Wireless sensor networks (WSN) are a pervasive means for business processes to interact in real time with the environment. In this paper, we analyze the business process model and notation (BPMN) standard with respect to its expressiveness for capturing the reactive, communication, and heterogeneous aspects of such WSN applications. Our analysis is based on a representative set of WSN applications for which we found the BPMN language adequate in capturing high-level specifications.

Energy-efficiency through micro-managing communication and optimizing sleep

Energy-efficiency is key to meet lifetime requirements of Wireless Sensor Networks (WSN) applications. Todays run-time platforms and development environments leave it to the application developer to manage power consumption. For best results, the characteristics of the individual hardware platforms must be well understood and minutely directed. An Operating System (OS) with suitable programming abstractions can micro-manage power consumption of resources. We demonstrate with the Mote Runner platform how the inherent overhead of managed application code is compensated for by a platform-independent communication API together with sleep optimizations. The proposed abstractions and optimizations can be applied to other modern sensor network platforms. To quantify the effectiveness of our approach, we measured the energy efficiency of a real-world WSN application using a custom TDMA communication protocol fully implemented on both Mote Runner and TinyOS. Mote Runners power management and sleep phase optimizations outperforms TinyOS in our test application for duty cycles below 10% on the Iris hardware.

From business process models to pervasive applications: Synchronization and optimization

Wireless sensor networks (WSN) have become the eyes and arms of business processes, far beyond production line automation, and have moved into the fabric of everyday life. Business processes describe the steps and interactions required to achieve a desired economic goal. Sensor networks are pervasively included in such processes from an early design phase using graphical models. However, automatically translating graphical descriptions to WSN platforms is a challenge. Graphical descriptions are typically based on a parallel execution model, whereas the norm for WSN is an event-based execution model on resource constrained platforms. We show how the synchronization primitives from a graphical business process modeling language can be mapped directly to efficient event-based code. Moreover, we explore platform-specific optimizations which enable the generated code to compete with hand-coded equivalents in terms of resource usage. For commercially attractive solutions we focus on reducing both the energy consumption as well as memory usage which directly impact the maintenance cost of a WSN.

A heterogeneous RSSI-based localization system for indoor and outdoor sports activities

Localization and tracking of players is crucial for monitoring both indoor and outdoor sports activities. The effects of the environment pose a major challenge for an accurate position estimation. In this paper, we present a novel solution based on the received signal strength indication (RSSI) feature provided by off-the-shelf wireless networks. Trilateration is used for estimating the position of targets with a RSSI to distance mapping function based on the path-loss shadowing propagation model. Key to our system is the real-time collection of RSSI measurements for which we designed and implemented a new, channel-hopping, TDMA-based protocol, which coordinates frame transmissions among nodes. A further innovative aspect of our solution is that the nodes are heterogeneous, using Waspmote and IRIS nodes as well as XBee modules. The latter enables a signicant boost in the transmit power, which in turn improves the resolution of the RSSI to distance estimates. Additionally, we address the challenges of fast deployment and testing by using a semi-automatic calibration mechanism for adjusting the distances estimated from RSSI measurements. Our experiments, conducted both indoors and outdoors, show that sub-meter accuracy can be achieved by combing a high transmit power, multiple channels, together with multiple antennas.

VILLASMART: Wireless sensors for system identification in domestic buildings

In this paper, we describe the design decisions, the implementation caveats, and the challenges faced while deploying a special-purpose wireless sensor network (WSN) at a domestic building that is part of a smart grid test environment. The sensor network is designed to collect high-quality data of the buildings in- and outdoor climate, heating system, and energy consumption. This rich sensor data is analyzed in order to characterize the buildings potential to act as a flexible energy consumer in a smart grid framework. In addition to the functional challenges, a continuous, low-power operation over extended periods as well as a plug&play, non-intrusive installation are required. Moreover, restrictions on the hardware costs and the development-to-deployment time had to be considered. Our simulation-driven application development and our highly modular design proved to be essential in meeting these challenges. This approach and its application to a real-world installation represent the key contributions of this work.