Klaas Thoelen

LooCI: a loosely-coupled component infrastructure for networked embedded systems

Considerable research has been performed in applying run-time reconfigurable component models to the domain of wireless sensor networks. The ability to dynamically deploy and reconfigure software components has clear advantages in sensor network deployments, which are typically large in scale and expected to operate for long periods in the face of node mobility, dynamic environmental conditions and changing application requirements. To date, research on component and binding models for sensor networks has primarily focused on the development of specialized component models that are optimized for use in resource-constrained environments. However, current approaches impose significant overhead upon developers and tend to use inflexible binding models based on remote procedure calls. To address these concerns, we introduce a novel component and binding model for networked embedded systems (LooCI). LooCI components are designed to impose minimal additional overhead on developers. Furthermore, LooCI components use a novel event-based binding model that allows developers to model rich component interactions, while providing support for easy interception, re-wiring and re-use. A prototype implementation of our component and binding model has been realised for the SunSPOT platform. Our preliminary evaluation shows that LooCI has an acceptable memory footprint and imposes minimal overhead on developers.

LooCI: The Loosely-coupled Component Infrastructure

Creating and managing applications for Wireless Sensor Networks (WSNs) is complicated by large scale, resource constraints and network dynamics. Reconfigurable component models minimize these complexities throughout the application lifecycle. However, contemporary component based middleware for WSNs is limited by its poor support for distribution. This paper introduces the Loosely-coupled Component Infrastructure (LooCI), a middleware for building distributed component-based WSN applications. LooCI advances the state-of-the-art by cleanly separating distributed concerns from component implementation, supporting application-level interoperability between heterogeneous WSN platforms and providing compatibility testing of bindings at runtime. Together, these features promote the safe and efficient composition and reconfiguration of distributed WSN applications. We evaluate the performance of LooCI on three classes of sensor nodes and demonstrate that these features can be provided with minimal overhead in terms of computation, memory and message passing.

Building Wireless Sensor Network Applications with LooCI

Considerable research has been performed in applying run-time reconfigurable component models to the domain of wireless sensor networks. The ability to dynamically deploy and reconfigure software components has clear advantages in sensor networks, which are typically large in scale and expected to operate for long periods in the face of node mobility, dynamic environmental conditions, and changing application requirements. LooCI is a component and binding model that is optimized for use in resource-constrained environments such as Wireless Sensor Networks. LooCI components use a novel event-based binding model that allows developers to model rich component interactions, while providing support for run-time reconfiguration, reflection, and policy-based management. This paper reports on the design of LooCI and describes a prototype implementation for the Sun SPOT. This platform is then evaluated in context of a real-world river monitoring and warning scenario in the city of Sao Carlos, Brazil.

Supporting reconfiguration and re-use through self-describing component interfaces

Run-time reconfigurable component models have been highlighted as having particular potential in networked embedded systems. In these models, explicit interface definitions promote the re-use of generic units of functionality between application compositions, while run-time reconfiguration provides a mechanism to manage the dynamism of sensor network environments. Despite these advantages, in current systems, reliably re-using and reconfiguring distributed components is a complex undertaking. It requires a detailed understanding of the services offered by each component. The lack hereof effectively precludes run-time discovery and use of third-party components. This paper proposes the embedding of compact semantic descriptions in component interfaces and associated messages. These descriptions allow for efficient compatibility checking and therefore facilitate the run-time discovery and use of third-party component services. We demonstrate that this scheme is feasible in even the most resource-constrained sensor network environments.

Types in Their Prime: Sub-typing of Data in Resource Constrained Environments

Sub-typing of data improves reuse and allows for reasoning at different levels of abstraction; however, it is seldom applied in resource constrained environments. The key reason behind this is the increase in overhead that is caused by including hierarchical information in data types as compared to a flat list. Where hierarchical data typing is used, it is often represented using verbose textual identifiers or numerical encodings that are suboptimal with regards to space. In this paper, we present an encoding function for hierarchically typed information, based on the properties of prime numbers. It provides a compact representation of types, fast subsumption testing even on resource constrained platforms and support for the evolution of the data type hierarchy. We demonstrate the feasibility of our approach on two representative communication models in constrained environments; a publish/subscribe event bus and a RESTful application protocol. We evaluate the performance of our encoding function and show that it has limited overhead compared to a flat list of data types and that this overhead is outweighed by reduced memory and communication overhead once applied.

A reconfigurable component model with semantic type system for dynamic WSN applications

Runtime reconfigurable component models provide several attractions with regard to the management of wireless sensor network (WSN) applications operating in dynamic environments and under evolving application requirements. One such attraction is the runtime discovery of suitable components for reuse in changing application compositions. Syntactic interface typing, provided by contemporary component models, however only supports exact interface matching. This causes limited reuse of components and complicates management of WSN applications. We argue that more flexibility is required to efficiently manage the complex, large-scale and dynamic WSN deployments of the future. In this paper, we describe the addition of semantic service descriptions to component interfaces to support compatibility and subtype testing. This allows rich discovery and reuse of third-party functionality and reasoning at the level of equivalent service types. We report on the incorporation of these semantic interface definitions in the Loosely Coupled Component Infrastructure (LooCI). Evaluation thereof shows that the scheme imposes minimal computational and memory overhead, while significantly reducing the complexity and cost of reconfiguration.

Component-based Orchestration of Dynamic IaaS Applications

Orchestration tools for Infrastructure-as-a-Service (IaaS) environments facilitate the deployment and management of cloud-based applications by automating the instantiation of virtual resources and configuration of software packages. While contemporary tools support the deployment of predefined applications, they lack internal support for taking care of changes in application designs. Dealing with this application dynamism in a timely manner requires new development and management techniques. This paper proposes a component-based approach that captures the entire design and runtime management cycle of IaaS applications. First, a component model is introduced that represents virtual computational resources as components and externalises control over their application logic. This model is then applied in a component framework that enables the rapid design of verified applications, and features additional support for the pre-provisioning of generic infrastructure and late configuration of application components. To showcase the capabilities of this approach, it is applied to an elastic media distribution use case.

StIgMa: Status information management for evolvable wireless sensor networks

The application of run-time evolvable software stacks promises an increase in the lifetime of wireless sensor network deployments. Besides supporting changing application requirements, said systems allow the underlying platforms to adapt to new environments by replacing system and communication services at runtime. These dynamics across various software layers however complicate the provision of accurate information about the current software and environmental status of a sensor node. This is problematic as sensor network management requires such information to configure efficient systems. As such, a mechanism needs to be in place via which run-time deployable software services can make their status information available to others in a standardized manner. In this paper we introduce StIgMa; a design for a unified node-local status registry on a sensor node. StIgMas interfaces are cross-cutting and provide access to status information on all software layers on a sensor node. This is achieved without duplication of status data and avoiding tight coupling of status information providers and clients. To allow multi-user and flexible operation, StIgMa is supported by an extensible namespace for status parameters and a query language. Evaluation of a proof-of-concept implementation confirms that node-local centralized management of status information can be realized in a light-weight manner.

Tracking and tracing containers through distributed sensor middleware

In a container transport system, wireless sensor networks (WSNs) can be used for monitoring products while they are being transported. To be commercially interesting, these WSNs must be integrated with enterprise systems of various actors in the supply chain. The need for interoperability between networks and partners, the heterogeneity of WSN technologies being used, and the mobility of sensor nodes make this integration far from trivial. This paper presents lessons learned from a research project in collaboration with industry in which we developed a prototype middleware solution for container transport. The prototype triggered valuable feedback which is highly relevant to consider when designing middleware for realistic sensor applications.

Middleware for Adaptive Group Communication in Wireless Sensor Networks

While the size and heterogeneity of wireless sensor networks confirm the need and benefit of group communication, an intelligent approach that exploits the interaction pattern and network context is still missing. This paper introduces sensor middleware to dynamically select the most efficient alternative from a set of group communication mechanisms. The proposed solution leverages on an empirical analysis of the ODMRP multicast protocol and was evaluated by a proof-of-concept prototype running on the SunSPOT platform. Results show that network overhead is considerably reduced when using the sensor middleware for software deployment, reconfiguration and periodic data monitoring.