On 1/22/23 16:05, Matthew Petach wrote:
On Sun, Jan 22, 2023 at 2:45 PM Michael Thomas <[email protected]> wrote:
I read in the Economist that the gen of starlink satellites will have
the ability to route messages between each satellite. Would
conventional
routing protocols be up to such a challenge? Or would it have to be
custom made for that problem? And since a lot of companies and
countries
are getting on that action, it seems like fertile ground for (bad)
wheel
reinvention?
Unlike most terrestrial links, the distances between satellites are
not fixed,
and thus the latency between nodes is variable, making the concept of
"Shortest Path First" calculation a much more dynamic and challenging
one to keep current, as the latency along a path may be constantly
changing
as the satellite nodes move relative to each other, without any link
state actually
changing to trigger a new SPF calculation.
I suspect a form of OLSR might be more advantageous in a dynamic partial
mesh between satellites, but I haven't given it as much deep thought
as would
be necessary to form an informed opinion.
So, yes--it's likely the routing protocol used will not be entirely
"off-the-shelf"
but will instead incorporate continuous latency information in the LSDB,
and path selection will be time-bound based on the rate of increase in
latency
along currently-selected edges in the graph.
Satellites move constantly relative to each other and to ground stations.
There is a database available which contains the parameters for
calculating a satellite's location at any instant in time.
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.
Then based upon latency, signal quality, and link availability, routing
information is inserted/deleted into the forwarding information base.
There are other contributors such as link saturation and overall
end-to-end delays which could be applied based upon ground station state
management.
It becomes a multi-parameter link selection algorithm in a dynamic
environment.
Pretty much an interesting 'sdn' like scenario.
