Re: [Starlink] fiber IXPs in space

[Ulrich Speidel <u.speidel@auckland.ac.nz>]

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On 17/04/2023 5:54 am, David Fernández via Starlink wrote:
> In case you put a DNS server in the satellite, so that it replies
> instead of a DNS server on ground, the RTT is reduced by half.
>
> The idea would be that the satellite inspects IP packets and when it
> detects a DNS query, instead of forwarding the packet to ground
> station, it just answers back to the sender of the query.
Understood - it's just that the gain you have from this is quite small. 
DNS queries only happen the first time a host needs to resolve a name, 
and then again after cache expiry much later, so they account for only a 
tiny fraction of the traffic, and also for only a small amount of the 
total delay in page loads. RTT isn't really the big issue in Starlink - 
yes it's larger than it perhaps needs to be, and bufferbloat seems to be 
present, but compared to GEO, it's now in the range seen for terrestrial 
Internet.
>
> Nowadays, satellites (starlink included) are still transparent and are
> signal repeaters, not routers processing IP packets, so doing this is
> not immediate at all, but it could bring some benefits.

Yes, but the benefits are quite small.

>
> CDNs or even datacenters (Cloud) in GEO or LEO is even more complex.

Indeed. In so many ways.

Mind though that CDNs are generally tied in with DNS nowadays, and 
there's another snag: Take two users, Alice in the UK and Bob in New 
Zealand - pretty much antipodean, using Starlink in bent-pipe 
configuration, i.e., their traffic goes through, say, the London gateway 
in the UK and the Clevedon gateway in NZ. Now imagine both trying to 
resolve the same CDN hostname some time apart, but via the same 
satellite DNS as the satellite has moved from the UK to NZ in the 
interim. Say Alice resolves first and gets the IP address of a CDN 
server in the UK. If the satellite DNS now caches this, and Bob queries 
the same hostname, he gets directed to a server in the UK literally a 
world away instead of the Auckland one closest to him. So unless each 
satellite carries a geolocated copy of the world's DNS entries with it 
and makes a decision based on user location, you have a problem.

>
> Regards,
>
> David
> _______________________________________________
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> Starlink@lists.bufferbloat.net
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> <https://lists.bufferbloat.net/listinfo/starlink>

-- 
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Dr. Ulrich Speidel

School of Computer Science

Room 303S.594 (City Campus)

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