Re: Starlink routing

[Raymond Burkholder <ray () oneunified net>]

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.