In this episode of PING, APNIC’s Chief Scientist Geoff Huston discusses Starlink, examining how modern TCP flow control algorithms manage the considerable variability in loss and delay evident across the satellite network. His recent investigations involve conducting measurements with Starlink terminals in both Australia and the USA, at various times of the day, to understand the system’s behaviour more comprehensively.
Starlink has broken new ground in Low Earth Orbit (LEO) Internet services. Unlike Geostationary Earth Orbit (GEO) satellite services, which have a long delay but constant visibility of the satellite in stationary orbit above, Starlink requires the consumer’s equipment to continuously reselect a new satellite as they move overhead in orbit. In fact, Starlink LEOs require a new satellite to be picked every 15 seconds. This means there’s a high degree of variability in the behaviour of the link, both between signal quality to each satellite, and in the brief interval of loss occurring at each satellite reselection window.
It’s a miracle TCP can survive, and even excel with protocols like BBR, under the right conditions. This is largely due to the transition from the traditional slow start, fast backoff model found in Cubic and Reno protocols to a more assertive approach in bandwidth estimation. With BBR, TCP continuously explores available bandwidth, pushing its throughput to remarkable levels when conditions allow.
Read more about satellites, TCP, and flow control algorithms on the APNIC Blog and the IETF website.
- An explainer on coherent optical transceivers
- Low Earth Orbit and the congestion control problem
- APNIC Labs measurements of Starlink
- Comparing TCP and QUIC
- Testing LEO and GEO Satellite Services in Australia
- Transport Protocols and the Network
- Congestion Control at IETF 110
Subscribe and share your story
You can stream and subscribe to PING via the following channels:
If you’re interested in sharing your insights or research, please get in touch — we’re always looking for great stories from the community. And please do let us know what you think of the podcast as well as the APNIC Blog so we can keep improving.
The views expressed by the authors of this blog are their own and do not necessarily reflect the views of APNIC. Please note a Code of Conduct applies to this blog.