[Starlink] mems optical switching

Mon Mar 20 14:55:06 EDT 2023

Not so fast! A number of issues here, and one of them is that the 
question itself is unclear. There are several levels of "working":

  * A satellite forwarding uplink traffic to an adjacent peer within the
    same orbital plane for downlink.
      o Dto for cross-plane
  * A satellite forwarding incoming laser link traffic to another
    satellite in the same orbital plane.
      o Dto for cross-plane
  * Routing to select destinations only.
  * Routing to everywhere.
  * Doing so efficiently globally under load.

I'm pretty sure that they are managing somewhere around the first 3-4 
major bullet points by now, with probably some outages (I note that 
Starlink now advertises global maritime coverage, at a price around 10 
times that of a land-based subscription). But the last point is where it 
truly gets hard.

The other thing worth remembering is that distance isn't necessarily a 
good indicator - it depends on where that distance accrues. Southern 
California to southern BC is around 2000 km, and the zone around the 
US-Canada border is where satellite density is highest - and capacity 
attracts in Starlink. Note also that gateways are generally in spots 
where there is little obstruction in terms of elevation, so in the case 
of Vancouver BC can probably serve birds that are just a few degrees 
over the horizon (which also helps keeping the beam out of geostationary 
trouble). Read: a lot stays bent pipe.

On 21/03/2023 12:46 am, Mike Puchol via Starlink wrote:
> I tested them in the middle of nowhere (literally) and it worked, no 
> gateways anywhere even close. Latencies varied between 20-30ms and up 
> to 400ms (to the POP), and there were occasional outages.
>
> What was fascinating was that I could predict when an outage would 
> take place by watching starlink.sx and seeing that the ISL-linked 
> satellites would dissapear from view with no others to take over, and 
> also predicting when I'd have service again by watching the next 
> ISL-linked sat approach the field-of-view.
>
> The other test I did was, while watching the tracker and the azimuth 
> to the satellite, place myself at the right position between the 
> antenna and the satellite, and confirm that the link would drop.
>
> All of the above was possible because a) there weren't that many ISL 
> satellites in orbit at the time, and b) the density of satellites in 
> the region I was testing was low, so only 1-2 satellites could be 
> serving my location at a time, making tests easier.
>
> Best,
>
> Mike
> On Mar 20, 2023 at 12:32 +0100, Dave Taht via Starlink 
> <starlink at lists.bufferbloat.net>, wrote:
>> We haven't heard much about the starlink ISL links lately. Any sign
>> they are working anywhere yet?
>>
>> On Sun, Mar 19, 2023 at 7:33 AM Christian von der Ropp via Starlink
>> <starlink at lists.bufferbloat.net> wrote:
>>>
>>> All-optical switching could greatly reduce complexity and power
>>> consumption on the satellites at the cost of flexibility. Up to 44
>>> satellites in an orbital plane would use individual wavelengths which
>>> would be passed on transparently down the daisy chain and only
>>> satellites in range of gateways would convert the optical signals back
>>> into electrical ones, and send them down to earth while they pass a
>>> gateway. This would result in relatively short duty cycles, hence less
>>> power draw per orbit and less heat dissipation issues.
>>>
>>> Actually I've been suspecting that the SDA targets all-optical switching
>>> for the Transport Layer constellation as I don't seen any other
>>> immediate reason for the requirement of their OISL standard to require
>>> wavelength switching within the ITU channel grid for LCTs (see p. 18 of
>>> the OISL 3.0:
>>> https://www.sda.mil/wp-content/uploads/2022/04/SDA-OCT-Standard-v3.0.pdf) 
>>> <https://www.sda.mil/wp-content/uploads/2022/04/SDA-OCT-Standard-v3.0.pdf)>
>>>
>>> As a matter of fact tuneable wavelenghts were already required in the
>>> draft version of the OISL standard published in April 2020:
>>> https://twitter.com/Megaconstellati/status/1310336728595562499 
>>> <https://twitter.com/Megaconstellati/status/1310336728595562499>
>>>
>>> -Christian
>>>
>>> Am 19.03.2023 um 16:16 schrieb Brandon Butterworth via Starlink:
>>>> On Sat Mar 18, 2023 at 03:19:49PM -0700, Dave Taht via Starlink wrote:
>>>>> Today, this about google's mems switching tech hit,
>>>> They've been talking about it since last year, seems to have got
>>>> a hype bump recently.
>>>>
>>>> Who expected circuit switching to make a comeback?
>>>>
>>>>> I keep wondering where else it could be applied.
>>>> They've been used for a long time, eg almost 20 years ago -
>>>> https://archive.nanog.org/meetings/nanog32/presentations/zwart.pdf 
>>>> <https://archive.nanog.org/meetings/nanog32/presentations/zwart.pdf>
>>>>
>>>> There is a goal of optical packet switching, until then you're
>>>> limited to where there are limited flows of long enough duration
>>>> to make the change from packet to circuit switching viable. So mostly
>>>> automated testing.
>>>>
>>>> I've dabbled with the idea in an archive use case where very few of
>>>> a large set of storage nodes need to connect to a moderate number
>>>> of servers. For some cases we could have zero switches. The goal was
>>>> a mostly dark infrastructure and many 1000s of storage nodes,
>>>> removing the switches saves a lot of power.
>>>>
>>>> Commercial optical switches are expensive so I was looking at
>>>> making an optical strowger as I wanted a high fan out not
>>>> large n^2.
>>>>
>>>> In the mobile world they are looking at doing flexible bandwidth
>>>> per node with coherent optics over gpon fibre plant, allocating
>>>> variable amounts of spectrum to each, which could be adapted to a
>>>> similar circuit model. It'd be no use to google as they want the
>>>> full bandwidth between each node but as dwdm coherent optic costs
>>>> come down you could imagine doing the same with a full channel
>>>> between each pair, so like a conventional WSS but cheaper. If it
>>>> wasn't for the optics cost I suspect they'd have done that reducing
>>>> switching time to a channel change.
>>>>
>>>> brandon
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>>>
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>>
>>
>>
>> --
>> Come Heckle Mar 6-9 at: https://www.understandinglatency.com/ 
>> <https://www.understandinglatency.com/>
>> Dave Täht CEO, TekLibre, LLC
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>
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-- 
****************************************************************
Dr. Ulrich Speidel

School of Computer Science

Room 303S.594 (City Campus)

The University of Auckland
u.speidel at auckland.ac.nz  
http://www.cs.auckland.ac.nz/~ulrich/
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