Towards a Service Oriented Architecture for Wireless Sensor Networks in Industrial Applications? Rudolf Sollacher, Christoph Niedermeier, Norbert Vicari ** Maxim Osipov *** (e-mail: firstname.lastname@siemens.com) ** Siemens AG, Corporate Technology, Munich, Germany *** OOO Siemens Corporate Technology, Moscow, Russia Abstract: We discuss the introduction of service oriented architectures to wireless sensor networks (WSN) in industrial applications. We give an example for a WSN architecture as applied in the EU project SOCRADES in order to explain constraints preventing a full-fledged service oriented approach. Such an approach appears to be beneficial for applications like diagnostics or monitoring where service composition can provide new functionalities. However, the limited resources in WSN must be taken into account. For control applications additional constraints like determinism or latency bound severly limit a loose coupling of services. As a consequence we propose a support by appropriate design and engineering tools. 1. INTRODUCTION Important trends like urbanization and demographic change will lead to an increasing scarcity of natural re- sources like energy and water, a growing need for envi- ronmental protection, increasing mobility, regional shift of economic gravity, individualization and shorter product life cycles. The corresponding challenges for manufactur- ing can be mastered with the concept of an “intelligent factory” with its seamless product and production life cycles linking the real and the digital world (Schott [2007]); product requirements, product use and service, plant op- timization, maintenance and operation are tightly linked to product and production design, simulation and virtual commissioning. The life cycle of an intelligent factory is characterized by four main steps: (i) Design and modern- ization is based on a holistic modeling, (ii) engineering takes advantage of autonomous components like working cells, (iii) commissioning is simplified by self-configuration of these interconnected autonomous components and (iv) operation benefits from self-optimization and self-healing functionality. As a consequence, each of these technological components carries with it an evolving “digital shadow” including knowledge of its state and current environment. This paper discusses wireless sensor networks (WSN) as one part of these autonomous technological components and their service-orientated integration in industrial au- tomation environments as planned in the European re- search project SOCRADES 1 . A major goal of this project is to create new methodologies, technologies and tools for the modeling, design, implementation and operation of networked hardware/software systems embedded in smart physical objects. Typically, each entity is constituted of hardware, sensing/actuating resources, control software and embedded intelligence. These entities are capable of working in a pro-active manner, initiating collaborative 1 http://www.socrades.eu actions and dynamically interacting with each other in order to achieve both local and global objectives, down from the physical machine control level up to the higher levels of the business process management system. One special - and due to its wireless communication infrastructure technologically very outstanding - instance for such embedded networked hardware/software systems on the sensor level of the automation pyramid are WSN. 2. WIRELESS SENSOR NETWORKS 2.1 Sensor node hardware The SOCRADES WSN architecture bases upon the as- sumption that the WSN will be connected to a wired network, utilizing a Gateway. While an Ethernet based wired control network allows for high bandwidth, a WSN is much more resource constrained. Sensor nodes used in SOCRADES are based on low power hardware compo- nents widely used for wireless sensor platforms. The mi- croprocessor (MSP430F1611) runs at 8 MHz and provides 10 kByte RAM and 48 kByte plus 256 Byte flash memory. The transceiver chip (CC2420) supports the IEEE 802.15.4 standard with maximum transmit power of 0dBm and maximum bandwidth of 250 kbit/s. Fig. 1. Hardware architecture of a typical sensor node.