I think the thing they're calling revolutionary is the idea of those links being directional lasers.

It makes some sense...  if you can basically emit the same signal you'd shoot down a strand of single mode but aim it through the mostly vacuum of space in the exact direction of your neighbor then you've got something...  Essentially the equivalent of a fiber optic network in space. 

For fun  I tried plugging in some frequencies of light into a doppler calculator.  Unfortunately that's where my "would the relative speed that mere mortals could attain make enough of a difference to affect a typical optical receiver" investigation ended as I'm mobile right now and can't do the rest of the work very easily.   I'd be curious if the relative speed would be enough to cause enough shift to move it out of the pass band if a typical dwdm channel.

And, I agree that little of what musk takes credit for is revolutionary.  But what I do think he deserves credit for is being insane enough to try things everyone says is unworkable and failed in the past and somehow making at least some of them work.  Having more money than God helps too. 



On Sun, Jan 22, 2023, 8:55 PM Tom Beecher <beecher@beecher.cc> wrote:
Yes re: Iridium. Contrary to what the Chief Huckster may say, inter-sat comms are not some revolutionary thing that he invented. 

It’s also not likely to function anything like they show in marketing promos, with data magically zipping around the constellation between nodes in different inclinations. Unless they have managed to solve for the Doppler effect in a way nobody has thought of yet. 
 

On Sun, Jan 22, 2023 at 18:25 Crist Clark <cjc+nanog@pumpky.net> wrote:
I suspect, although I have no references, that satellite to ground connectivity is probably more “circuit-based” than per-packet or frame.

Iridium has done inter satellite communication for decades. I wonder if it wouldn’t be something very similar. Although it would be totally on-brand for them to do it some “revolutionary” new way whether it actually makes any sense or not.


On Sun, Jan 22, 2023 at 3:06 PM Matthew Petach <mpetach@netflight.com> 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?

Mike



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.

An interesting problem to dive into, certainly.   :)

Thanks!

Matt