Comment by ggreer
1 year ago
Optical fiber has an index of refraction of around 1.6, so signals travel at around 0.6c. For a perfectly straight cross-continental link (5,000km) with no delays from amplification/retransmission, that's about 26 milliseconds. Assuming the satellites are directly overhead, Starlink adds another 500km up and down, making the minimum possible latency around 20 milliseconds. The real number might be slightly higher or lower depending on the location of the satellites.
My guess is the real latency depends mostly on the latency of relay nodes (either satellites or routers on earth), not the medium through which signals travel.
Number of hops definitely matters more usually. For example I'm about 150 miles from Azure East US 2 (richmond, va), and at the speed of light that should be sub 2ms round trip, but actual latency to it is ~30ms. But I'm sure I'm going through dozens of switches/routers to get there. What Starlink buys you is that you get to go straight to a satellite, then a laser in a vacuum to other satellite(s) and then a ground station that's likely already at an IXP or very close to one.
Could also be shit routing.
Some big ISPs here refused to locally peer with some cheaper providers, so some packets to a local data centre (5 miles away) in Toronto would round trip through Chicago and back.
If they wanted a direct connection; they wanted them to pay for transit.