Re: [Starlink] Starlink hidden buffers

[Ulrich Speidel <u.speidel@auckland.ac.nz>]

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On 14/05/2023 6:55 pm, David Lang wrote:
>
> 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 
> <https://www.amazon.com/YAOSHENG-Rectangular-Adapter-Connect-Injector/dp/B0BYJTHX4P>
>
I'll see whether I can get hold of one of these. Cutting a cable on a 
university IT asset as an academic is not allowed here, except if it 
doesn't meet electrical safety standards.

Alternatively, has anyone tried the standard Starlink Ethernet adapter 
with a PoE injector instead of the WiFi box? The adapter above seems to 
be like the Starlink one (which also inserts into the cable between 
Dishy and router).

> > 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.
Really? I'm thinking stuff like the sudden addition of packets from 
potentially dozens of TCP flows with large cwnd's?
>
> > 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 the reverse is almost certainly not true: Each satellite must serve 
multiple cells.
> 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.
Well, we do know for NZ, sort of, based on the licences Starlink has here.
>
> And remember that for every cell that a satellite takes over, it's 
> also giving
> away one cell at the same time.
Yes, except that some cells may have no users in them and some of them 
have a lot (think of a satellite flying into range of California from 
the Pacific, dropping over-the-water cells and acquiring land-based ones).
>
> I'm not saying that the problem is trivial, but just that it's not unique
What makes me suspicious here that it's not the usual bufferbloat 
problem is this: With conventional bufferbloat and FIFOs, you'd expect 
standing queues, right? With Starlink, we see the queues emptying 
relatively occasionally with RTTs in the low 20 ms, and in some cases 
under 20 ms even. With large ping packets (1500 bytes).
>
> David Lang

-- 
****************************************************************
Dr. Ulrich Speidel

School of Computer Science

Room 303S.594 (City Campus)

The University of Auckland
u.speidel@auckland.ac.nz  
http://www.cs.auckland.ac.nz/~ulrich/
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