On Sun, 14 May 2023, Ulrich Speidel wrote:
On 14/05/2023 10:57 am, David Lang wrote:
On Sat, 13 May 2023, Ulrich Speidel via Starlink wrote:
Here's a bit of a question to you all. See what you make of it.
I've been thinking a bit about the latencies we see in the Starlink
network. This is why this list exist (right, Dave?). So what do we know?
1) We know that RTTs can be in the 100's of ms even in what appear to be
bent-pipe scenarios where the physical one-way path should be well under
3000 km, with physical RTT under 20 ms.
2) We know from plenty of traceroutes that these RTTs accrue in the
Starlink network, not between the Starlink handover point (POP) to the
Internet.
3) We know that they aren't an artifact of the Starlink WiFi router (our
traceroutes were done through their Ethernet adaptor, which bypasses the
router), so they must be delays on the satellites or the teleports.
the ethernet adapter bypasses the wifi, but not the router, you have to cut
the cable and replace the plug to bypass the router
Good point - but you still don't get the WiFi buffering here. Or at least we
don't seem to, looking at the difference between running with and without the
adapter.
wifi is an added layer, with it's own problems, eliminating those problems when
testing the satellite link is the first step, but it would also be a good idea
to take the next step and bypass the router.
I just discovered that someone is manufacturing an adapter so you no longer have
to cut the cable
https://www.amazon.com/YAOSHENG-Rectangular-Adapter-Connect-Injector/dp/B0BYJTHX4P
Put another way: If you have a protocol (TCP) that is designed to reasonably
expect that its current cwnd is OK to use for now is put into a situation
where there are relatively frequent, huge and lasting step changes in
available BDP within subsecond periods, are your underlying assumptions still
valid?
I think that with interference from other APs, WIFI suffers at least as much
unpredictable changes to the available bandwidth.
I suspect they're handing over whole cells, not individual users, at a time.
I would guess the same (remember, in spite of them having launched >4000
satellites, this is still the early days, with the network changing as more are
launching)
We've seen that it seems that there is only one satellite serving any cell at
one time. But remember that the system does know how much usage there is in the
cell before they do the handoff. It's unknown if they do anything with that, or
if they are just relaying based on geography. We also don't know what the
bandwidth to the ground stations is compared to the dishy.
And remember that for every cell that a satellite takes over, it's also giving
away one cell at the same time.
I'm not saying that the problem is trivial, but just that it's not unique
David Lang
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