[Podcast] Low Earth Orbit and the TCP congestion control problem

By on 23 Nov 2023

Category: Tech matters

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Traffic Jam on Coronation Drive, 1954
Adapted from the original at the State Library of Queensland.

In this episode of PING, APNIC’s Chief Scientist Geoff Huston discusses the rise of Low Earth Orbit (LEO) satellite-based Internet and the consequences for end-to-end congestion control in TCP and related protocols.

Modern TCP has mostly been tuned for constant delay low loss paths and performs very well at balancing bandwidth among the cooperating users of such a link, achieving maximum use of the resource.

However, a consequence of the new LEO Internet is a high degree of variability in delay, loss and, consequently, an unstable bandwidth, which means TCP congestion control methods aren’t working quite as well in this kind of Internet. With the emergence of TCP bandwidth estimation models such as Bottleneck Bandwidth and Round-trip propagation time (BBR) and the rise of new transports like QUIC (that continue to use the classic TCP model for congestion control), we have a fundamental mismatch in how competing flows try to share the link.

Geoff has been testing these issues with Starlink home routers and models of satellite visibility. The APNIC Labs Starlink page visualizes Starlink system behaviour and satellites in orbit.

Read more about TCP, QUIC, LEO and Geoff’s measurements on the APNIC Blog and APNIC Labs:

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