From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from vsmx002.dclux.xion.oxcs.net (vsmx002.dclux.xion.oxcs.net [185.74.65.108]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 289383B2A4 for ; Thu, 28 Oct 2021 06:53:07 -0400 (EDT) Received: from proxy-2.proxy.oxio.ns.xion.oxcs.net (proxy-2.proxy.oxio.ns.xion.oxcs.net [41.90.113.162]) by mx-out.dclux.xion.oxcs.net (Postfix) with SMTP id B37978C02D9; Thu, 28 Oct 2021 10:53:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=dclux.xion.oxcs.net; s=mail1; t=1635418386; bh=0qTBwg9YAgIJiy8xCjIZ1uktdY+J4aJKt8X8bEn60rk=; h=Date:From:To:Cc:In-Reply-To:References:Subject:From; b=mkZ7a3RDK1zzsBiVt1QtPvzgG1whz2xppxLm+qlkErQym/h92Ey8Q/004/oQFlXDn 1X4XcTqGuqStWPHzH7rgkyK2kVy4DkkjGEGt80SbrR7VH3hzugRqCQZKklFKjCOj37 zh6Gu4RHOB+66Cx/v+jNFwwRMvnaethlRnWCUQm0L9ySzrULICf6aMzk7tfnHX9TV+ NUeZ/bNWTxB9TE2HWP3zAleMNvxpW5eNNwHVhLLM8IqE9NbwUXGN5JJW3RrqlZKXWJ Td1/T3BabvAInNrHLfwbT/nZ9u3XV//AfK0MbwfINfdgjxAz9vOGKywpWU63kRzfn4 HWyien336gjxA== Date: Thu, 28 Oct 2021 13:52:51 +0300 From: Mike Puchol To: Michael Richardson , Ulrich Speidel Cc: starlink@lists.bufferbloat.net Message-ID: In-Reply-To: References: <28034.1635270711@localhost> <8007.1635359366@localhost> X-Readdle-Message-ID: da668f87-99f4-44cd-a5ee-750c7b84d48a@Spark MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="617a8109_5fb8011c_28c9" X-VadeSecure-Status: LEGIT X-VADE-STATUS: LEGIT Subject: Re: [Starlink] thinking about the laser links again X-BeenThere: starlink@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Starlink has bufferbloat. Bad." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 28 Oct 2021 10:53:07 -0000 --617a8109_5fb8011c_28c9 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline I cannot add more than the real experts on the networking / topology side= , but on the lasers themselves, a question was raised about multiple link= s. The only way to do it economically is to use a single optical train pe= r link (includes laser TX and photon detector, mirrors, power control, at= tenuators, etc.). I raised the idea of an =46SOC =E2=80=9Cflashlight=E2=80=9D to what could= be counted as people in the top 10 worldwide list of experts in the fiel= d. Here, a beam would be made wide enough to have multiple =E2=80=9Cclien= ts=E2=80=9D, as for radio sector antennas. The idea was quickly discarded= for a number of reasons, the principal being that you are spreading the = photons so much that not enough would reach the other side, at least at a= ny meaningful distance. Photon detectors that could work are in the scientific instrument categor= y, thus really expensive. =46rom photos, we know that each satellite has at least two lasers, so we= can assume at least in-plane communications. Best, Mike On Oct 28, 2021, 11:01 +0300, Ulrich Speidel = , wrote: > On 28/10/2021 7:29 am, Michael Richardson wrote: > > > I guess the real question is: have you written the Hollywood Security= > > Theatre > > script based upon this issues, and can I play the geek that explains > > this=3F :-) > Sure=21 > > > > > - Tell satellites where to send packets (in something along the > > lines of a > > > long header, as in AX.25 for example). Then a sending ground statio= n > > would > > > need a complete almanach of the constellation and an idea as to > > where the > > > receiving ground station is, and which satellite it would use for t= he > > > downlink. Pros: The sending ground station can do all the number > > crunching on > > > ground rather than space power. Cons:=C2=A0 Header size costs bandw= idth. > > > > =46rom what I understood, Starlink shipped some kind of comodity SDN = capable > > chip. So MPLS, or SRv6 ought to be easy, costing only a few bytes > > interpreted in hardware, and a path computation element on the ground= > > should > > be able to deal with the calculation. > > > > It's a challenging situation perhaps because the network effectively = gets > > rewired every few minutes, but ground based computation should be abl= e to > > deal with the problem. > > That presumes that the ground station has complete topology information= > for the constellation, though. That includes knowing about defective > satellites and lasers etc., birds deviating from assigned orbit. > > But in principle, I can see how that could work, yes. > > > > > > - Get the satellites to work out where stuff needs to be sent. If > > they were > > > to use something like Bellman-=46ord here, that would require an en= ormous > > > amount of update traffic. Dijkstra would require complete topology > > > information, which should in principle be computable from an > > almanach on the > > > satellites. > > > > I think, but I might be wrong, that there is a pattern which repeats > > over and > > over again. Just need to update the mapping of which satellite is in = which > > position in the precomputed mesh. No need to send the entire mesh. > > Of course. Bellman-=46ord & Co. all assume a network without such > regularities. But you need to make use of those patterns in order to > make things possible - whether you do source or hop-to-hop routing. And= > while the configuration of the network is indeed predictable at least > for the near future, it's not simply repeating over and over again. The= > current constellation (if viewed in isolation) more or less runs in 95 > minute cycles. Earth rotates under the constellation, so the teleports > only return to the same position with respect to the constellation when= > multiples of the length of a sidereal day coincide with multiples of 95= > minutes. Plus you may find that the Starlink constellation isn't > perfectly regular either in its pattern. > > > > -- > **************************************************************** > Dr. Ulrich Speidel > > School of Computer Science > > Room 303S.594 (City Campus) > Ph: (+64-9)-373-7599 ext. 85282 > > The University of Auckland > ulrich=40cs.auckland.ac.nz > http://www.cs.auckland.ac.nz/=7Eulrich/ > **************************************************************** > > > > =5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F= =5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F=5F > Starlink mailing list > Starlink=40lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/starlink --617a8109_5fb8011c_28c9 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline
I cannot add more than the real experts on the netw= orking / topology side, but on the lasers themselves, a question was rais= ed about multiple links. The only way to do it economically is to use a s= ingle optical train per link (includes laser TX and photon detector, mirr= ors, power control, attenuators, etc.).&=23160;

I raised the idea of an =46SOC =E2=80=9Cflashlight=E2=80=9D to what could= be counted as people in the top 10 worldwide list of experts in the fiel= d. Here, a beam would be made wide enough to have multiple =E2=80=9Cclien= ts=E2=80=9D, as for radio sector antennas. The idea was quickly discarded= for a number of reasons, the principal being that you are spreading the = photons so much that not enough would reach the other side, at least at a= ny meaningful distance.

Photon detectors that could work are in the scientific instrument categor= y, thus really expensive.

=46rom photos, we know that each satellite has at least two lasers, so we= can assume at least in-plane communications.

Best,

Mike
On Oct 28, 2021, 11:01 +0300, Ulric= h Speidel <ulrich=40cs.auckland.ac.nz>, wrote:
On 28/10/2021 7:29 am, Michael Richardson wrote:

I guess the real question is: have you writ= ten the Hollywood Security
Theatre
script based upon this issues, and can I play the geek that explains
this=3F :-)
Sure=21

- Tell satellites where to send packets (in= something along the
lines of a
long header, as in AX.25 for example). Then= a sending ground station
would
need a complete almanach of the constellati= on and an idea as to
where the
receiving ground station is, and which sate= llite it would use for the
downlink. Pros: The sending ground station can do all the number
crunching on
ground rather than space power. Cons:&=2316= 0; Header size costs bandwidth.

=46rom what I understood, Starlink shipped some kind of comodity SDN capa= ble
chip. So MPLS, or SRv6 ought to be easy, costing only a few bytes
interpreted in hardware, and a path computation element on the ground
should
be able to deal with the calculation.

It's a challenging situation perhaps because the network effectively gets=
rewired every few minutes, but ground based computation should be able to=
deal with the problem.

That presumes that the ground station has complete topology information for the constellation, though. That includes knowing about defective
satellites and lasers etc., birds deviating from assigned orbit.

But in principle, I can see how that could work, yes.


- Get the satellites to work out where stuf= f needs to be sent. If
they were
to use something like Bellman-=46ord here, = that would require an enormous
amount of update traffic. Dijkstra would require complete topology
information, which should in principle be computable from an
almanach on the
satellites.

I think, but I might be wrong, that there is a pattern which repeats
over and
over again. Just need to update the mapping of which satellite is in whic= h
position in the precomputed mesh. No need to send the entire mesh.
<= /blockquote>
Of course. Bellman-=46ord & Co. all assume a network without such
regularities. But you need to make use of those patterns in order to
make things possible - whether you do source or hop-to-hop routing. And while the configuration of the network is indeed predictable at least
for the near future, it's not simply repeating over and over again. The current constellation (if viewed in isolation) more or less runs in 95 minute cycles. Earth rotates under the constellation, so the teleports only return to the same position with respect to the constellation when multiples of the length of a sidereal day coincide with multiples of 95 minutes. Plus you may find that the Starlink constellation isn't
perfectly regular either in its pattern.



--
****************************************************************
Dr. Ulrich Speidel

School of Computer Science

Room 303S.594 (City Campus)
Ph: (+64-9)-373-7599 ext. 85282

The University of Auckland
ulrich=40cs.auckland.ac.nz
http://www.cs.auckland.ac.nz/=7Eulrich/
****************************************************************



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