Implementation of the EXI Schema on Wireless Sensor Nodes Using Contiki

The current trend in Wireless Sensor Networks (WSN) is to use the Internet Protocol (IP) and open standards to achieve native connectivity between smart objects and the Internet, contributing to consolidate the Internet of Things (IoT). Emerging standards such as 6LoWPAN/IPv6 and CoRE/CoAP will play a very important role in a Restful Web of Things, where each node has its own IPv6 address and is able to provide information and control about itself. Data exchanging in Machine To Machine (M2M) applications and communication with Web services require the use of structured data. XML is a possible solution, but its verbosity is not suitable for a WSN (e.g. based on IEEE 802.15.4) characterized by limited packet size. This paper investigates the benefits of Efficient XML Interchange (EXI) in a real scenario, considering sensor nodes running on the Contiki RTOS. For this purpose, the authors have implemented an extremely lightweight version of EXI for Contiki running on application boards with just 8 Kbyte RAM memory.