On 1/22/23 16:05, Matthew Petach wrote:

On Sun, Jan 22, 2023 at 2:45 PM Michael Thomas <mike@mtcc.com> 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.