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<div dir="auto">I cannot add more than the real experts on the networking / topology side, but on the lasers themselves, a question was raised about multiple links. The only way to do it economically is to use a single optical train per link (includes laser TX and photon detector, mirrors, power control, attenuators, etc.). <br />
<br />
I raised the idea of an FSOC “flashlight” to what could be counted as people in the top 10 worldwide list of experts in the field. Here, a beam would be made wide enough to have multiple “clients”, as for radio sector antennas. The idea was quickly discarded for a number of reasons, the principal being that you are spreading the photons so much that not enough would reach the other side, at least at any meaningful distance.<br />
<br />
Photon detectors that could work are in the scientific instrument category, thus really expensive.<br />
<br />
From photos, we know that each satellite has at least two lasers, so we can assume at least in-plane communications.</div>
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<div class="matchFont">Best,<br />
<br />
Mike</div>
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<div name="messageReplySection">On Oct 28, 2021, 11:01 +0300, Ulrich Speidel <ulrich@cs.auckland.ac.nz>, wrote:<br />
<blockquote type="cite" style="border-left-color: grey; border-left-width: thin; border-left-style: solid; margin: 5px 5px;padding-left: 10px;">On 28/10/2021 7:29 am, Michael Richardson wrote:<br />
<br />
<blockquote type="cite">I guess the real question is: have you written the Hollywood Security<br />
Theatre<br />
script based upon this issues, and can I play the geek that explains<br />
this? :-)<br /></blockquote>
Sure!<br />
<blockquote type="cite"><br />
<blockquote type="cite">- Tell satellites where to send packets (in something along the<br /></blockquote>
lines of a<br />
<blockquote type="cite">long header, as in AX.25 for example). Then a sending ground station<br /></blockquote>
would<br />
<blockquote type="cite">need a complete almanach of the constellation and an idea as to<br /></blockquote>
where the<br />
<blockquote type="cite">receiving ground station is, and which satellite it would use for the<br />
downlink. Pros: The sending ground station can do all the number<br /></blockquote>
crunching on<br />
<blockquote type="cite">ground rather than space power. Cons: Header size costs bandwidth.<br /></blockquote>
<br />
From what I understood, Starlink shipped some kind of comodity SDN capable<br />
chip. So MPLS, or SRv6 ought to be easy, costing only a few bytes<br />
interpreted in hardware, and a path computation element on the ground<br />
should<br />
be able to deal with the calculation.<br />
<br />
It's a challenging situation perhaps because the network effectively gets<br />
rewired every few minutes, but ground based computation should be able to<br />
deal with the problem.<br /></blockquote>
<br />
That presumes that the ground station has complete topology information<br />
for the constellation, though. That includes knowing about defective<br />
satellites and lasers etc., birds deviating from assigned orbit.<br />
<br />
But in principle, I can see how that could work, yes.<br />
<br />
<blockquote type="cite"><br />
<blockquote type="cite">- Get the satellites to work out where stuff needs to be sent. If<br /></blockquote>
they were<br />
<blockquote type="cite">to use something like Bellman-Ford here, that would require an enormous<br />
amount of update traffic. Dijkstra would require complete topology<br />
information, which should in principle be computable from an<br /></blockquote>
almanach on the<br />
<blockquote type="cite">satellites.<br /></blockquote>
<br />
I think, but I might be wrong, that there is a pattern which repeats<br />
over and<br />
over again. Just need to update the mapping of which satellite is in which<br />
position in the precomputed mesh. No need to send the entire mesh.<br /></blockquote>
<br />
Of course. Bellman-Ford & Co. all assume a network without such<br />
regularities. But you need to make use of those patterns in order to<br />
make things possible - whether you do source or hop-to-hop routing. And<br />
while the configuration of the network is indeed predictable at least<br />
for the near future, it's not simply repeating over and over again. The<br />
current constellation (if viewed in isolation) more or less runs in 95<br />
minute cycles. Earth rotates under the constellation, so the teleports<br />
only return to the same position with respect to the constellation when<br />
multiples of the length of a sidereal day coincide with multiples of 95<br />
minutes. Plus you may find that the Starlink constellation isn't<br />
perfectly regular either in its pattern.<br />
<br />
<br />
<br />
--<br />
****************************************************************<br />
Dr. Ulrich Speidel<br />
<br />
School of Computer Science<br />
<br />
Room 303S.594 (City Campus)<br />
Ph: (+64-9)-373-7599 ext. 85282<br />
<br />
The University of Auckland<br />
ulrich@cs.auckland.ac.nz<br />
http://www.cs.auckland.ac.nz/~ulrich/<br />
****************************************************************<br />
<br />
<br />
<br />
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Starlink mailing list<br />
Starlink@lists.bufferbloat.net<br />
https://lists.bufferbloat.net/listinfo/starlink<br /></blockquote>
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