Making Sense of Constellations: Methodologies for Understanding Starlink's Scheduling Algorithms

TL;DR

This paper investigates Starlink's hierarchical scheduling system using high-fidelity measurements, revealing the global and on-satellite controllers, and develops a predictive model for satellite allocation with high accuracy.

Contribution

It introduces a novel measurement-based approach to understand Starlink's scheduling algorithms and creates a model that accurately predicts satellite allocations.

Findings

Identified hierarchical traffic controllers in Starlink.

Developed a method to determine satellite-to-terminal allocations.

Built a model predicting satellite assignments with high accuracy.

Abstract

Starlink constellations are currently the largest LEO WAN and have seen considerable interest from the research community. In this paper, we use high-frequency and high-fidelity measurements to uncover evidence of hierarchical traffic controllers in Starlink -- a global controller which allocates satellites to terminals and an on-satellite controller that schedules transmission of user flows. We then devise a novel approach for identifying how satellites are allocated to user terminals. Using data gathered with this approach, we measure the characteristics of the global controller and identify the factors that influence the allocation of satellites to terminals. Finally, we use this data to build a model which approximates Starlink's global scheduler. Our model is able to predict the characteristics of the satellite allocated to a terminal at a specific location and time with reasonably high accuracy and at a rate significantly higher than baseline.