Guido Moritz

Beyond 6LoWPAN: Web Services in Wireless Sensor Networks

To date, Wireless Sensor Networks (WSN) require their own specific methodologies, tools, and technologies. With the rise of 6LoWPAN protocols (i.e., IPv6 over Low Power Wireless Personal Area Networks), WSNs can use IP to share a common network layer with other networks and the Internet for highly interoperable device communication. But additional efforts are necessary to develop new or adapt existing application layer protocols for IP-enabled WSNs. Hence, this paper investigates W3C SOAP Web Services (WS) in the context of WSNs. In particular, it is shown that the Devices Profile for Web Services (DPWS) can be used as an application layer protocol in WSNs.

Encoding and Compression for the Devices Profile for Web Services

Most solutions for Wireless Sensor Networks (WSN) come equipped with their own architectural concepts which raise the problem of possible incompatibility of computer networks and the WSN. Often gateway concepts are used to overcome this problem. But this is not the best solution on the long term. Other research fields and industrial domains are heading for universal cross domain architecture concepts based on internet technologies that are more mature and better understood. The IETF 6LoWPAN working group provides the groundings for standardized communication using existing network protocols like IPv6 also in low power radio networks. A big challenge when deploying further application layer network protocols on top of 6LoWPAN is the message size of existing mostly XML based protocols which does not meet the resource requirements of deeply embedded devices without further research efforts. This paper presents different data compression techniques for the Devices Profile of Web Services (DPWS) to be applied in 6LoWPAN networks. Therefore, we analyze a realistic scenario. We determined 18 message types in the scenario and compressed and encoded all messages by using existing schemes and tools. For the first time, we also investigate on the Efficient XML Interchange (EXI) format for DPWS.

WS4D: Toolkits for Networked Embedded Systems Based on the Devices Profile for Web Services

As the application of the Internet Protocol (IP) is not longer restricted to the internet and computer networks, future IP-based application scenarios require an enormous diversity of heterogeneous platforms and systems. Thereby emerging communication architectures, concepts, technologies and protocols must be capable of handling thousands of devices and communication endpoints on the one hand and be flexible and extensible enough on the other hand, to provide cross domain interoperability independent of platform specific constraints. The Devices Profile for Web Services (DPWS) is such a cross domain technology. This paper provides an overview of DPWS and existing DPWS implementations and toolkits with special focus on the Web Service for Devices (WS4D) initiative. Therefore, features and capabilities of DPWS are described in detail by referring to the open source WS4D implementations. The target platforms are ranging from resource rich server platforms down to highly resource constrained embedded devices.

Web services on deeply embedded devices with real-time processing

Service-oriented architectures become more and more important in connecting devices with each other. The main advantages of service-oriented architectures are higher abstraction level and interoperability of devices. In this field Web services become the most important standard for communication between devices. But this upcoming technology is only available on powerful devices. Embedded hardware is often excluded from the deployment of Web services because of the lack of resources like computing power and memory. In this area also real-time capabilities for process control are required. This paper presents a new approach to handle Web services communication on deeply embedded hardware with the devices profile for Web services specification.

Devices Profile for Web Services in Wireless Sensor Networks: Adaptations and enhancements

For Service-oriented Architectures, Web Services are claimed as state of the art to connect business execution layers as well as networking devices. Additionally, the deployment of Wireless Sensor Networks became applicable over the last years. The usage of application layer gateways and proxy concepts allow the integration of these sensor networks into real world scenarios and existing networks that make use of Web Services. This paper presents a new approach to adapt and enhance the Devices Profile for Web Services to be applied in Wireless Sensor Networks directly. Thus, seamless connectivity between business layers, device level networks, and Wireless Sensor Networks are possible.

Implementing powerful Web Services for highly resource-constrained devices

Web Service technologies are state of the art in current enterprise distributed applications. To integrate highly resource-constrained devices, such as sensor nodes, into enterprise applications via Web Services, gateways are commonly used. Our aim was to investigate the intermediate, homogeneous communication between enterprise applications and highly resource-constrained devices. We therefore present the prototype implementation of an embedded enterprise compatible W3C Web Service solution. Furthermore, we give an evaluation of memory requirements and a timing analysis for a representative platform with 48 KiB of ROM, 10 KiB of RAM and IEEE 802.15.4 radio. As the prototype implementation requires only 8:5 KiB of ROM and 3 KiB of RAM, our results claim that enterprise Web Services, despite of prevailing assumptions, are feasible in this context.

A Lightweight SOAP over CoAP Transport Binding for Resource Constraint Networks

A huge momentum towards IP enabled Wireless Sensor Networks (WSN) appeared through the emerging 6LoWPAN protocols (i.e. IPv6 over Low power Wireless Personal Area Networks). By using existing cross domain open standards in contrast of proprietary solutions, technologies and deployments are not tailored too tight for specific applications. Nevertheless, 6LoWPAN is only the first step. Still efforts on higher layers on top of 6LoWPAN are an urgent need to provide the seamless connectivity and interaction of highly resource constrained devices with higher valued applications and services. This paper describes a new approach to bind SOAP to the emerging Constrained Application Protocol (CoAP) protocol. Thereby, CoAP provides a lightweight but reliable transport binding for SOAP. Compared to the widespread TCP based HTTP binding, round trip times can be reduced by 43% in an exemplary scenario because of the omitted expensive bidirectional TCP handshake mechanisms. Combined with dedicated XML compressors like EXI, SOAP based protocols become also applicable in WSNs.

Web Services to improve interoperability of home healthcare devices

Home healthcare can be divided into monitoring and assistance scenarios. In both scenarios, miscellaneous devices are applied for dedicated sensor or actuator functionalities. The requirements and assumptions for the different nodes split the devices in three different classes with particular characteristics concerning energy consumption, power supply, memory, computing power, and bandwidth. Nevertheless, the number of nodes and complexity of setups require new concepts like Service-oriented Architectures to solve arising problems. In this paper, the Devices Profile for Web Services is suggested as comprehensive middleware for all three device classes. Hence, Web services technologies, which are already applied in the internet and in automation industry, can avoid interoperability problems of sensors and actors in the domain of home healthcare also.

Devices Profile for Web Services and the REST

For future application scenarios of resource constrained and low cost smart cooperating objects, miscellaneous technologies for wireless connectivity are existing or upcoming in the near future. But further cross domain middleware and dedicated communication protocols to provide syntactic and semantic interoperability and not only technical interoperability are still missing. Thus, this paper investigates on two major candidates for IP based low power communication, based on known and matured technologies and protocols. Therefore, analyses and pitfalls of RESTful architectures based on HTTP and the Devices Profile for Web Services are presented. Furthermore, the paper discusses differences of DPWS and RESTful design and furthermore proposes an approach for a generic mapping of emerging Bluetooth Low Energy technology with RESTful device architectures for seamless and transparent connectivity.

Towards Robust Data Storage in Wireless Sensor Networks

Abstract Wireless sensor networks are used for sensing data if wired communication is not suitable. Connection losses and depletion of nodes, however, result in reduced data availability of such networks. This is problematic in upcoming scenarios like health care or home automation where data availability is highly important. In this paper, we present an approach to provide robust data storage for wireless sensor networks. We achieve this goal by providing FAME-DBMS, a customizable database management system which can be tailored according to the varying requirements of a sensor network. FAME-DBMS provides reliable data storage using security and integrity features, transaction management and recovery and a customizable query engine. Since data reliability in wireless sensor networks also suffers from node failures, we propose a new S - RAID storage layer inspired from the RAID approach of server systems. This S-RAID is integrated in FAME-DBMS to store data redundantly and distributed in a wireless sensor network and thus provides access to data even when nodes fail.