Zephyr: Efficient Incremental Reprogramming of Sensor Nodes using Function Call Indirections and Difference Computation

Wireless reprogramming of sensor nodes is an essential requirement for long-lived networks since the software functionality changes over time. The amount of information that needs to be wirelessly transmitted during reprogramming should be minimized since reprogramming time and energy depend chiefly on the amount of radio transmissions. In this paper, we present a multihop incremental reprogramming protocol called Zephyr that transfers the delta between the old and the new software and lets the sensor nodes rebuild the new software using the received delta and the old software. It reduces the delta size by using application-level modifications to mitigate the effects of function shifts. Then it compares the binary images at the byte-level with a novel method to create small delta, that is then sent over the wireless network to all the nodes. For a wide range of software change cases that we experimented with, we find that Zephyr transfers 1.83 to 1987 times less traffic through the network than Deluge, the standard reprogramming protocol for TinyOS, and 1.14 to 49 times less than an existing incremental reprogramming protocol by Jeong and Culler.