Understanding the Challenges of Internet Congestion Control in LEO Satellite Networks

Satellite mega-constellations, such as those developed by Starlink and OneWeb, are transforming the landscape of global internet connectivity by extending access to the remotest parts of the world. Leveraging Low Earth Orbit (LEO) satellite networks, these systems operate at altitudes of 550-2,000km, relaying user data through ground stations and Points of Presence (PoP) to the broader internet. Additionally, some satellites are equipped with Inter-Satellite Laser Links (ISLs), enabling coverage for areas far removed from ground stations, including aircraft and maritime users. However, despite their revolutionary capabilities, the dynamic and ever-changing nature of LEO networks poses unique challenges to traditional congestion control mechanisms designed for terrestrial internet infrastructures.

How LEO Dynamics Impact Congestion Control

In LEO satellite networks, the forwarding path between user terminals and ground stations changes frequently due to the rapid movement of satellites orbiting Earth. These constant path changes result in fluctuating bottleneck capacities, delays, and packet loss rates. Unfortunately, conventional end-to-end congestion avoidance algorithms often misinterpret these fluctuations as signs of actual congestion when, in reality, they stem from the natural dynamics of LEO networks. These misinterpretations cause significant throughput inefficiencies and hinder the ability to effectively manage network resources.

Real-world performance data collected from tests with widely used congestion control algorithms (CCAs) such as Cubic, Vegas, and BBR further highlight the inadequacy of traditional methods in LEO environments. For instance, loss-based algorithms like Cubic suffer significant drops in throughput due to path changes misread as congestion signals. Model-based mechanisms such as BBRv1 and even improved versions like BBRv3 struggle to adapt to the highly variable bandwidth and loss rates of LEO networks, often leading to high delays and performance bottlenecks. On the other hand, machine learning-driven approaches, despite their promise, are often unable to converge effectively in dynamic LEO conditions, resulting in inefficient data transmission and sustained queuing delays.

Introducing LeoCC: A Tailored Solution for LEO Networks

To address the complexities of LEO dynamics, researchers from Tsinghua University have developed LeoCC, a congestion control algorithm specifically designed for satellite networks in LEO. Unlike traditional CCAs, LeoCC integrates a novel reconfiguration awareness mechanism that accounts for the dynamic nature of LEO network paths. By analyzing patterns in ACK (Acknowledgment) intervals, LeoCC dynamically adjusts to reconfiguration events, discarding outdated network data that could otherwise distort congestion control decisions. This approach ensures that the algorithm bases its decisions on current network states, thereby significantly reducing inefficiencies caused by outdated or misleading measurements.

Experimental data comparing LeoCC with other CCAs under various simulated LEO network conditions show a remarkable improvement in balancing throughput and delay. By incorporating a dynamic bottleneck model, LeoCC adapts quickly to the challenges posed by satellite reconfigurations, offering a robust and efficient solution for next-generation satellite internet services. Such advancements not only enhance end-user experiences but also provide valuable insights for network operators and engineers working to unlock the true potential of LEO networks.

The Future of Internet Connectivity in LEO

The rapid evolution of LEO satellite networks represents a pivotal moment for global connectivity, enabling internet access in regions previously considered unreachable. However, as these networks become more widespread, addressing the unique challenges they present, such as the limitations of existing congestion control methods, has become increasingly important. Innovations like LeoCC pave the way for more resilient and high-performing satellite internet systems, fostering further research and development in this burgeoning field.

As the research community continues to refine solutions for LEO-specific challenges, the open-source nature of tools like LeoCC provides a collaborative framework for progress. By addressing the core bottlenecks of current technologies, these advancements will play a crucial role in shaping the future of satellite internet and global connectivity.