Some interesting insight yesterday: One of my PhD student Wayne Reiher's
contacts on Tarawa atoll in Kiribati (pronounced "Kiri-bus"), Karotu
Tannang, operates a Starlink kit there, around 4,200 km north of
Auckland, New Zealand. Wayne asked him to run a few traceroutes and five
minute pings with large packets to get us an initial idea as to how well
it worked and how the signal got back to the rest of the world.
Tarawa is well out of bent-pipe range of any known Starlink gateways, so
would have to rely on laser ISLs.
All traces (to NZ, Chile, the US, Germany and Japan) exited the SpaceX
address space in New Zealand to a variety of upstream providers. IP
addresses on the Starlink side of the trace beyond Dishy are, in order
of appearance in the traces: 100.64.0.1, 172.16.249.6, followed by
149.19.109.30 if exiting to Hurricane Electric as upstream or
149.19.109.34 if exiting to Kinect. All those addresses have RTT
indicating that they are in NZ.
Lowest RTT seen to the first NZ hop was 65 ms, with values between 100
and 200 ms being the most common.
RTTs to the US were mostly in the high 200 ms.
Packet loss was atrocious: about 5% to NZ, 8% to Japan and Chile, 9% to
the US. Hard to say whether this was just due to variation on the leg to
NZ or whether anything got dropped further down the road.
First thoughts:
1) There is no 53 / 53.2 deg orbital plane for Starlink that is
simultaneously visible from both Tarawa and NZ. Unless the traceroutes
all happened to be piggybacking on one of the few polar orbit passing
overhead, this implies at least some degree of cross-plane forwarding.
We'll ask Karotu to run a few more tests for us at different times.
2) The fact that we don't see more than the "usual" number of Starlink
IP addresses in the tracreroutes indicates that whatever IP routing may
be happening on satellites that handle the traffic via ISLs happens at a
tunnel layer further down the stack.
3) The fact that the traffic emerges in New Zealand regardless of global
destination also indicates that the Starlink network uses a tunnel based
on Dishy location and a nearby gateway but does not attempt to route to
final destination at this point in time.
The 65 ms RTT also tells us a few things. For one, at 4,200 km great
circle distance on the ground, the dishy-to-gateway physical path would
be at least 5,000 km even if all lined up with a polar orbital plane
involved. That makes 10,000 km of RTT path, which translates into about
33 ms of propagation RTT. If cross-plane routing were involved here,
we'd get a zig-zag path - so roughly 1 1/2 times longer. Makes about 50
ms. In-plane only routing would involve a gateway in Australia (similar
length physical path dishy to gateway) along with a 2,000 km
trans-Tasman cable leg. The 2000 km cable leg would be equivalent to
about 20 ms of additional RTT over the 10,000 km space RTT path, so that
could in principle also work. Quite why everything would emerge in
Auckland though in this case would be a mystery to me.
--
****************************************************************
Dr. Ulrich Speidel
School of Computer Science
Room 303S.594 (City Campus)
The University of Auckland
[email protected]
http://www.cs.auckland.ac.nz/~ulrich/
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