Active Monitoring with RTLola: A Specification-Guided Scheduling Approach

TL;DR

This paper introduces an active monitoring approach using RTLola, where the monitor dynamically schedules sensor queries based on specification annotations, leading to more efficient and timely violation detection in resource-constrained systems.

Contribution

It presents a novel specification-guided scheduling method for active monitoring with RTLola, improving efficiency and responsiveness over passive, fixed-frequency monitoring.

Findings

Active scheduling reduces bandwidth usage while maintaining detection speed.

The approach detects violations significantly sooner than fixed-frequency sampling.

Performance demonstrated on aerospace domain specifications.

Abstract

Stream-based monitoring is a well-established runtime verification approach which relates input streams, representing sensor readings from the monitored system, with output streams that capture filtered or aggregated results. In such approaches, the monitor is a passive external component that continuously receives sensor data from the system under observation. This setup assumes that the system dictates what data is sent and when, regardless of the monitor's current needs. However, in many applications -- particularly in resource-constrained environments like autonomous aircraft, where energy, size, or weight are limited -- this can lead to inefficient use of communication resources. We propose making the monitor an active component that decides, based on its current internal state, which sensors to query and how often. This behavior is driven by scheduling annotations in the specification, which guide the dynamic allocation of bandwidth towards the most relevant data, thereby improving monitoring efficiency. We demonstrate our approach using the stream-based specification language RTLola and assess the performance by monitoring a specification from the aerospace domain. With equal bandwidth usage, our approach detects specification violations significantly sooner than monitors sampling all inputs at a fixed frequency.