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<div class="moz-cite-prefix">On 1/22/23 16:05, Matthew Petach wrote:<br>
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cite="mid:CAEmG1=q_N-2UfZLZCUQG3=SaBJMpykC3iUJeDzPFR6=1+s8GMQ@mail.gmail.com">
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<div dir="ltr" class="gmail_attr">On Sun, Jan 22, 2023 at 2:45
PM Michael Thomas <<a href="mailto:mike@mtcc.com"
moz-do-not-send="true" class="moz-txt-link-freetext">mike@mtcc.com</a>>
wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">I read in the Economist
that the gen of starlink satellites will have <br>
the ability to route messages between each satellite. Would
conventional <br>
routing protocols be up to such a challenge? Or would it
have to be <br>
custom made for that problem? And since a lot of companies
and countries <br>
are getting on that action, it seems like fertile ground for
(bad) wheel <br>
reinvention?</blockquote>
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<div>Unlike most terrestrial links, the distances between
satellites are not fixed, </div>
<div>and thus the latency between nodes is variable, making
the concept of <br>
"Shortest Path First" calculation a much more dynamic and
challenging </div>
<div>one to keep current, as the latency along a path may be
constantly changing </div>
<div>as the satellite nodes move relative to each other,
without any link state actually</div>
<div>changing to trigger a new SPF calculation.</div>
<div><br>
</div>
<div>I suspect a form of OLSR might be more advantageous in a
dynamic partial </div>
<div>mesh between satellites, but I haven't given it as much
deep thought as would </div>
<div>be necessary to form an informed opinion.</div>
<div><br>
</div>
<div>So, yes--it's likely the routing protocol used will not
be entirely "off-the-shelf" </div>
<div>but will instead incorporate continuous latency
information in the LSDB, </div>
<div>and path selection will be time-bound based on the rate
of increase in latency </div>
<div>along currently-selected edges in the graph.</div>
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</blockquote>
<br>
Satellites move constantly relative to each other and to ground
stations.<br>
<br>
There is a database available which contains the parameters for
calculating a satellite's location at any instant in time.<br>
<br>
To maintain minimal link disruption, the idea is to calculate these
relative relationships, and using some graph and network flow
algorithms, you pre-calculate the links and then insert/remove those
links and routes into the routing information base at the
appropriate times. <br>
<br>
Then based upon latency, signal quality, and link availability,
routing information is inserted/deleted into the forwarding
information base.<br>
<br>
There are other contributors such as link saturation and overall
end-to-end delays which could be applied based upon ground station
state management.<br>
<br>
It becomes a multi-parameter link selection algorithm in a dynamic
environment.<br>
<br>
Pretty much an interesting 'sdn' like scenario.<br>
<br>
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