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. This paper presents an improved DPWS architecture that takes into account the requirements of WSNs. For instance, in order to reduce overhead, messages are scaled down by an optimized data encoding based on the emerging W3C Efficient XML Interchange (EXI) format. Moreover, a novel SOAP-binding on top of the IETF Constrained Application Protocol (CoAP) is introduced for an efficient transport of SOAP messages. The paper evaluates the proposed approaches by dedicated implementations of DPWS, EXI, and the SOAP-over-COAP binding. The results claim that the proposed approaches satisfy the requirements of mote class devices with only tens of KB RAM and ROM.