[Starlink] fiber IXPs in space
Ulrich Speidel
u.speidel at auckland.ac.nz
Sun Apr 16 22:08:44 EDT 2023
On 17/04/2023 1:04 pm, David Lang wrote:
> I think it is going to be fairly common, but the beauty of the idea is
> that you don't have to risk much to try it. Long lived DNS answers
> (and especially root servers and TLD servers) can trivially be
> mirrored to the satellites, and you can experiment with caching to see
> what sort of hit rate you get. Even if you don't cache a lot of the
> CDN type traffic, it should still be a win to have the longer term
> stuff there.
Yes - but root servers and TLD servers also get cached a long time at
the clients. If each of your clients needs a root server and a few TLD
lookups a day, it's not a huge gain in terms of performance.
It is however a significant step up in terms of complexity. E.g., your
satellite-based DNS would have to point you at the TLD server that is
topologically closest to your Starlink gateway, or risk a potentially
much longer RTT for the lookup. So you'd need to maintain a list of TLD
instances on your satellite-based DNS and return the one that
corresponds to what your gateway-based DNS would get. Sure possible but
more complex than a bog standard DNS server in a fixed network.
>
>> Practically speaking, we know from various sources that each Starlink
>> satellite provides - ballpark - a couple of dozen Gb/s in capacity,
>> and that active users on a "busy" satellite see a couple of dozen
>> Mb/s of that. "Busy" means most active users, and so we can conclude
>> that the number of users per satellite who use any site is at most
>> around 1000. The subset of users navigating to new sites among them
>> is probably in the low 100's at best. If we're excluding new sites
>> that aren't dynamic, we're probably down to a couple of dozen new
>> static sites being queried per satellite pass. How many of these
>> queries will be duplicates? Not a lot. If we're including sites that
>> are dynamic, we're still not getting a huge probability of cache
>> entry re-use.
>
> I think that each user is typically going to use a lot less than the
> 'couple dozen MB' that is the limits that we see, so the number of
> users in a cell would be much higher.
Yes, but these users aren't "active" in the sense that they will be
firing off DNS queries during the pass...
>
>>> DNS data is not that large, getting enough storage into the
>>> satellites to serve 90% of the non-dynamic data should not be a big
>>> deal. The dynamic data expires fast enough (and can be detected as
>>> being dynamic and expired faster in the satellite) that I'm not
>>> worried about serving data from one side of the world to the other.
>> Yes, but the only advantage we'd get here is faster resolution for a
>> very small subset of DNS queries.
>
> and while that's not as big a win as faster resolution of a larger
> set, it's still a win.
Yes, but are we chasing diminishing margins here when there are much
bigger fish to fry?
>
> There are various things that could be done if there is enough
> interest in starlink users to improve the CDN traffic, and it's not
> clear that misdirecting starlink users in some (or even many) cases
> would be that horrible. Geolocation is very imprecise at best and
> routinely misidentifies locations.
See my comments on geolocation in my response to David Reed's post - I
shouldn't have used that term.
--
****************************************************************
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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