A wireless sensor network protocol for the OMG Data Distribution Service

Wireless Sensor Network technologies are maturing into industrial applicability, but the availability of broadly supported architectures and integration of existing standards is still lagging behind. As a proposal to ameliorate this situation, we consider the OMG Data Distribution Service (DDS), a middleware standard for interoperable data-centric publish/subscribe architectures with real-time capabilities, a candidate for standards-based realisations of equally data-centric WSN scenarios. DDS is rooted in larger-scale architectures. Consequently, the RTPS network protocol defined as a sibling standard to DDS assumes Ethernet-sized network frames and substantial communication resources, which are potential obstacles to applying DDS to WSNs. We therefore propose SNPS as an alternative transport protocol for DDS communication. SNPS has been designed as part of sDDS, a model-driven DDS realization architecture supporting highly resource-constrained embedded sensor node platforms. Still, SNPS is generally independent of sDDS; it was demonstrated to be usable even with minimalist solutions lacking a proper DDS run-time system. For SNPS, a modular layered architecture focussing on minimum footprint and scalability was defined. SNPS packets are assembled from an extensible set of submessages that are chosen and filled according to a well-defined, unambiguous protocol state engine. Keeping a stack of context information for a stream of SNPS submessages minimizes explicit state representation in the resulting packet structure. Other aspects of the protocol design are the support for bundling of data to minimize the total number of link layer frames exchanged and the leveraging of multi- and broadcast properties of wireless sensor networks. Most of the features are beneficial for wired sensor networks as well. SNPS has been implemented for several wireless and wired network protocols (ZigBee, 6LoWPAN, and Ethernet/UDP/IP) on diverse embedded sensor node and PC platforms. It has been embedded in the sDDS architecture and integrated into minimalist standalone implementations. It will be the main DDS transport protocol used at sensor integration levels of current projects of the authors' laboratory research group targeting home and industrial automation scenarios.