From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from tuna.sandelman.ca (tuna.sandelman.ca [209.87.249.19]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id C245E3CB41 for ; Wed, 27 Oct 2021 14:29:29 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by tuna.sandelman.ca (Postfix) with ESMTP id C4FB91801E; Wed, 27 Oct 2021 14:30:35 -0400 (EDT) Received: from tuna.sandelman.ca ([127.0.0.1]) by localhost (localhost [127.0.0.1]) (amavisd-new, port 10024) with LMTP id 85g1T9NP-P4O; Wed, 27 Oct 2021 14:30:33 -0400 (EDT) Received: from sandelman.ca (obiwan.sandelman.ca [IPv6:2607:f0b0:f:2::247]) by tuna.sandelman.ca (Postfix) with ESMTP id A1D311801B; Wed, 27 Oct 2021 14:30:33 -0400 (EDT) Received: from localhost (localhost [IPv6:::1]) by sandelman.ca (Postfix) with ESMTP id 7C8F2585; Wed, 27 Oct 2021 14:29:26 -0400 (EDT) From: Michael Richardson To: Ulrich Speidel cc: starlink@lists.bufferbloat.net In-Reply-To: References: <28034.1635270711@localhost> X-Mailer: MH-E 8.6+git; nmh 1.7+dev; GNU Emacs 26.1 X-Face: $\n1pF)h^`}$H>Hk{L"x@)JS7<%Az}5RyS@k9X%29-lHB$Ti.V>2bi.~ehC0; <'$9xN5Ub# z!G,p`nR&p7Fz@^UXIn156S8.~^@MJ*mMsD7=QFeq%AL4m 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: Wed, 27 Oct 2021 18:29:29 -0000 --=-=-= Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Ulrich Speidel wrote: > Lasers vs. RF (microwave): The problem with RF is that it's comparati= vely > difficult to produce a sharp beam as you can do with lasers - mostly = due to > the fact that the wavelength involved is so much larger (centimeter > scale vs Yeah, I knew that, but I was thinking that the shaper beam is a negative due to effort pointing it so precisely. Maybe some layer/RF hybrid. > Both lasers and RF suffer from one common problem, though: If the tra= nsmitter > is in front of the sun from the receiver's perspective, then sun's wi= deband > signal is all the receiver will see. I guess the real question is: have you written the Hollywood Security Theat= re script based upon this issues, and can I play the geek that explains this? = :-) > - 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 constellation and an idea as to where= the > receiving ground station is, and which satellite it would use for the > downlink. Pros: The sending ground station can do all the number crun= ching on > ground rather than space power. Cons:=C2=A0 Header size costs bandwid= th. From=20what 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 able to deal with the problem. > - Get the satellites to work out where stuff needs to be sent. If the= y were > to use something like Bellman-Ford here, that would require an enormo= us > 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 a= nd 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. One might be able to use RPL(RFC6550) for this, which avoids sending update= traffic if there is no real traffic. =2D- ] Never tell me the odds! | ipv6 mesh network= s [ ] Michael Richardson, Sandelman Software Works | IoT architect = [ ] mcr@sandelman.ca http://www.sandelman.ca/ | ruby on rails = [ --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCgAdFiEEbsyLEzg/qUTA43uogItw+93Q3WUFAmF5moYACgkQgItw+93Q 3WVE/Af/SjSHzOPry6Yt6PNtRVU4hjUGDWLHvuzCA0IdARa+goxkwUVhtxIqzfxX yixAaLSMyIYH5zMFASX9VXhadYzjv7LXiNR89gXxvw9Zo4QydaMLI1eOmPy6esA/ qmFaKky2Upr5eiOprNRF/yoGYnES2C0Y3Cpacn5Mi+4CJkDXENWAoRLb/sfH0Iyl Rbg35nGe5s1k5X17UGSy4VatB9CxBpcAnPezZrF4m/cbAAwBdittbHRCHfKXrEKf CwN/B3zkAizFsrTeulM9NNdUvqTiqfZD4n2BXFScK7/vYU3QcicbHLUlWHz9mO55 M1/ZSEnHgIddWJvH/4qTbWE/Dg0fow== =NzPs -----END PGP SIGNATURE----- --=-=-=--