Abstract
Wireless Sensor Networks (WSNs) are used in a wide variety of applications including environmental monitoring, electrical grids, and manufacturing plants. WSNs are plagued by the possibility of bugs manifesting only at deployment. However, debugging deployed WSNs is challenging for several reasons—the remote location of deployed nodes, the non-determinism of execution, and the limited hardware resources available. A primary debugging mechanism, record and replay, logs a trace of events while a node is deployed, such that the events can be replayed later for debugging. Existing recording methods for WSNs cannot capture the complete code execution, thus negating the possibility of a faithful replay and causing some bugs to go unnoticed. Existing approaches are not resource efficient enough to capture all sources of non-determinism. We have designed, developed, and verified two novel approaches to solve the problem of practical record and replay for WSNs.
Our first approach, Aveksha, uses additional hardware to trace tasks and other generic events at the function and task level. Aveksha does not need to stop the target processor, making it non-intrusive. Using Aveksha we have discovered a previously unknown bug in a common operating system.
Our second approach, Tardis, uses only software to deterministically record and replay WSN nodes. Tardis is able to record all sources of non-determinism, based on the observation that such information is compressible using a combination of techniques specialized for respective sources. We demonstrate Tardis by diagnosing a newly discovered routing protocol bug.
