On the Safety Implications of Misordered Events and Commands in IoT Systems

TL;DR

This paper investigates how network delays in IoT systems cause misordered events and commands, leading to potential safety issues, and evaluates the prevalence of this problem across major platforms and real-world deployments.

Contribution

It identifies root causes of event and command misordering in IoT systems and provides a formal analysis and empirical evaluation of the problem's extent.

Findings

Major IoT platforms lack strong event ordering guarantees.

High incidence of misordered events and commands in simulated smart home.

Root causes of misordering are formally analyzed and characterized.

Abstract

IoT devices, equipped with embedded actuators and sensors, provide custom automation in the form of IoT apps. IoT apps subscribe to events and upon receipt, transmit actuation commands which trigger a set of actuators. Events and actuation commands follow paths in the IoT ecosystem such as sensor-to-edge, edge-to-cloud, and cloud-to-actuator, with different network and processing delays between these connections. Significant delays may occur especially when an IoT system cloud interacts with other clouds. Due to this variation in delays, the cloud may receive events in an incorrect order, and in turn, devices may receive and actuate misordered commands. In this paper, we first study eight major IoT platforms and show that they do not make strong guarantees on event orderings to address these issues. We then analyze the end-to-end interactions among IoT components, from the creation of an event to the invocation of a command. From this, we identify and formalize the root causes of misorderings in events and commands leading to undesired states. We deploy 23 apps in a simulated smart home containing 35 IoT devices to evaluate the misordering problem. Our experiments demonstrate a high number of misordered events and commands that occur through different interaction paths. Through this effort, we reveal the root and extent of the misordering problem and guide future work to ensure correct ordering in IoT systems.