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<div class="moz-cite-prefix">On 17/04/2023 5:54 am, David Fernández
via Starlink wrote:<br>
</div>
<blockquote type="cite" cite="mid:CAC=tZ0qrB4Eqj-7nwXirB-2x0oya0Kmgfi1_8QptmOP904D=nQ@mail.gmail.com">
In case you put a DNS server in the satellite, so that it replies<br>
instead of a DNS server on ground, the RTT is reduced by half.<br>
<br>
The idea would be that the satellite inspects IP packets and when
it<br>
detects a DNS query, instead of forwarding the packet to ground<br>
station, it just answers back to the sender of the query.<br>
</blockquote>
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.<br>
<blockquote type="cite" cite="mid:CAC=tZ0qrB4Eqj-7nwXirB-2x0oya0Kmgfi1_8QptmOP904D=nQ@mail.gmail.com"><br>
Nowadays, satellites (starlink included) are still transparent and
are<br>
signal repeaters, not routers processing IP packets, so doing this
is<br>
not immediate at all, but it could bring some benefits.<br>
</blockquote>
<p>Yes, but the benefits are quite small.</p>
<blockquote type="cite" cite="mid:CAC=tZ0qrB4Eqj-7nwXirB-2x0oya0Kmgfi1_8QptmOP904D=nQ@mail.gmail.com"><br>
CDNs or even datacenters (Cloud) in GEO or LEO is even more
complex.<br>
</blockquote>
<p>Indeed. In so many ways.</p>
<p>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.<br>
</p>
<blockquote type="cite" cite="mid:CAC=tZ0qrB4Eqj-7nwXirB-2x0oya0Kmgfi1_8QptmOP904D=nQ@mail.gmail.com"><br>
Regards,<br>
<br>
David<br>
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</blockquote>
<pre class="moz-signature" cols="72">--
****************************************************************
Dr. Ulrich Speidel
School of Computer Science
Room 303S.594 (City Campus)
The University of Auckland
<a class="moz-txt-link-abbreviated" href="mailto:u.speidel@auckland.ac.nz">u.speidel@auckland.ac.nz</a>
<a class="moz-txt-link-freetext" href="http://www.cs.auckland.ac.nz/~ulrich/">http://www.cs.auckland.ac.nz/~ulrich/</a>
****************************************************************
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