If Starlink satellites are processing IP packets, shouldn't them be shown in traceroutes? They are not shown now, AFAIK.
A transparent geographical based routing could be possible, with signal-pass-through approach to the next satellite on a path connecting to a GW, via ISL, if the satellite receiving traffic from a dishy does not have any GW at direct sight. > Date: Thu, 1 Sep 2022 09:46:20 +1200 > From: Ulrich Speidel <[email protected]> > To: [email protected] > Subject: Re: [Starlink] Starlink "beam spread" > Message-ID: <[email protected]> > Content-Type: text/plain; charset="utf-8"; Format="flowed" > > I work on the assumption that Starlink satellites are, or at least will > eventually be, processing IP packets. For inter-satellite routing it's > more or less a must-have unless you have some other packet switching > protocol layered in between. > > On 1/09/2022 2:51 am, David Fernández via Starlink wrote: >> "DNS on Starlink satellites: Good idea, lightweight, and I'd suspect >> maybe already in operation?" >> >> Are the satellites processing IP packets? Are the ISLs even in >> operation? I have been told Starlink satellites are transparent. >> >> >> > Date: Thu, 1 Sep 2022 01:41:07 +1200 >> > From: Ulrich Speidel <[email protected]> >> > To: David Lang <[email protected]> >> > Cc: Sebastian Moeller <[email protected]>, Ulrich Speidel via Starlink >> > <[email protected]> >> > Subject: Re: [Starlink] Starlink "beam spread" >> > Message-ID: <[email protected]> >> > Content-Type: text/plain; charset=UTF-8; format=flowed >> > >> > Um, yes, but I think we're mixing a few things up here (trying to bundle >> > responses here, so that's not just to you, David). >> > >> > In lieu of a reliable Starlink link budget, I'm going by this one: >> > >> > >> https://www.linkedin.com/pulse/quick-analysis-starlink-link-budget-potential-emf-david-witkowski/ >> >> <https://www.linkedin.com/pulse/quick-analysis-starlink-link-budget-potential-emf-david-witkowski> >> > >> > Parameters here are a little outdated but the critical one is the EIRP >> > at the transmitter of up to ~97 dBm. Say we're looking at a 30 GHz Ka >> > band signal over a 600 km path, which is more reflective of the current >> > constellation. Then Friis propagation gives us a path loss of about 178 >> > dB, and if we pretend for a moment that Dishy is actually a 60 cm >> > diameter parabolic dish, we're looking at around 45 dBi receive antenna >> > gain. Probably a little less as Dishy isn't actually a dish. >> > >> > Then that gives us 97 dBm - 178 dB + 45 dB = -36 dBm at the ground >> > receiver. Now I'm assuming here that this is for ALL user downlink beams >> > from the satellite combined. What we don't really know is how many >> > parallel signals a satellite multiplexes into these, but assuming at the >> > moment a receive frontend bandwidth of about 100 MHz, noise power at the >> > receiver should be around 38 pW or -74 dBm. That leaves Starlink around >> > 38 dB of SNR to play with. Shannon lets us send up to just over 1.25 >> > Gb/s in that kind of channel, but then again that's just the Shannon >> > limit, and in practice, we'll be looking a a wee bit less. >> > >> > That SNR also gives us an indication as to the signal separation Dishy >> > needs to achieve from the beams from another satellite in order for that >> > other satellite to re-use the same frequency. Note that this is >> > significantly more than just the 3 dB that the 3 dB width of a beam >> > gives us. The 3 dB width is what is commonly quoted as "beam width", and >> > that's where you get those nice narrow angles. But that's just the width >> > at which the beam drops to half its EIRP, not the width at which it can >> > no longer interfere. For that, you need the 38 dB width - or thereabouts >> > - if you can get it, and this will be significantly more than the 1.2 >> > degrees or so of 3dB beam width. >> > >> > But even if you worked with 1.2 degrees at a distance of 600 km and you >> > assumed that sort of beam width at the satellite, it still gives you an >> > >12 km radius on the ground within which you cannot reuse the downlink >> > frequency from the same satellite. That's orders of magnitude more than >> > the re-use spatial separation you can achieve in ground-based cellular >> > networks. Note that the 0.1 deg beam "precision" is irrelevant here - >> > that just tells me the increments in which they can point the beam, but >> > not how wide it is and how intensity falls off with angle, or how bad >> > the side lobes are. >> > >> > Whether you can re-use the same frequency from another satellite to the >> > same ground area is a good question. We really don't know the beam >> > patterns that we get from the birds and from the Dishys, and without >> > these it's difficult to say how much angular separation a ground station >> > needs between two satellites using the same frequency in order to >> > receive one but not be interfered with by the other. Basically, there >> > are just too many variables in this for me to be overly optimistic that >> > re-use by two different sources within a Starlink cell is possible. And >> > I haven't even looked at the numbers for Ku band here. >> > >> > CDNs & Co - are NOT just dumb economic optimisations to lower bit miles. >> > They actually improve performance, and significantly so. A lower RTT >> > between you and a server that you grab data from via TCP allows a much >> > faster opening of the congestion window. With initial TCP cwnd's being >> > typically 10 packets or around 15 kB of data, having a server within 10 >> > ms of your client means that you've transferred 15 kB after 5 ms, 45 kB >> > after 10 ms, 105 kB after 15 ms, 225 kB after 20 ms, and 465 kB after 25 >> > ms. Make your RTT 100 ms, and it takes half a second to get to your 465 >> > kB. Having a CDN server in close topological proximity also generally >> > reduces the number of queues between you and the server at which packets >> > can die an untimely early death, and generally, by taking load off such >> > links, reduces the probability of this happening at a lot of queues. >> > Bottom line: Having a CDN keeps your users happier. Also, live streaming >> > and video conferencing aside, most video is not multicast or broadcast, >> > but unicast. >> > >> > DNS on Starlink satellites: Good idea, lightweight, and I'd suspect >> > maybe already in operation? It's low hanging fruit. CDNs on satellites: >> > In the day and age of SSDs, having capacity on the satellite shouldn't >> > really be an issue, although robustness may be. But heat in this sort of >> > storage gets generated mostly when data is written, so it's a function >> > of what percentage of your data that reaches the bird is going to end up >> > in cache. Generally, on a LEO satellite that'll have to cache baseball >> > videos while over the US, videos in a dozen different languages while >> > over Europe, Bollywood clips while over India, cooking shows while over >> > Australia and always the same old ads while over New Zealand, all the >> > while not getting a lot of cache hits for stuff it put into cache 15 >> > minutes ago, would probably have to write a lot. Moreover, as you'd be >> > reliant on the content you want being on the satellite that you are >> > currently talking to, pretty much all satellites in the constellation >> > would need to cache all content. In other words: If I watch a cat video >> > now and thereby put it into the cache of the bird overhead, and then >> > send you an e-mail and you're in my neighbourhood and you watch it half >> > an hour later, my satellite would be on the other side of the world, and >> > you'd have to have it re-uploaded to the CDN on the bird that's flying >> > overhead our neighbourhood then. Not as efficient as a ground-based CDN >> > on our ground-based network that's fed via a satellite link. >> > >> > As long as Starlink is going to have in the order of hundreds of >> > thousands of direct users, that problem won't go away. >> > >> > On 31/08/2022 7:33 pm, David Lang wrote: >> > >> >> On Wed, 31 Aug 2022, Ulrich Speidel via Starlink wrote: >> >> >> >>> This combines with the uncomfortable truth that an RF "beam" from a >> >>> satellite isn't as selective as a laser beam, so the options for >> >>> frequency re-use from orbit aren't anywhere near as good as from a >> >>> mobile base station across the road: Any beam pointed at you can be >> >>> heard for many miles around and therefore no other user can re-use >> >>> that frequency (with the same burst slot etc.). >> >> >> >> not quite, you are forgetting that the antennas on the ground are also >> >> steerable arrays and so they can focus their 'receiving beam' at >> >> different satellites. This is less efficient than a transmitting beam >> >> as the satellites you aren't 'pointed' at will increase your noise >> >> floor, but it does allow the same frequency to be used for multiple >> >> satellites into the same area at the same time. >> >> >> >> David Lang >> >> >> > -- >> > **************************************************************** >> > 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/ >> <http://www.cs.auckland.ac.nz/~ulrich> >> > **************************************************************** >> > >> _______________________________________________ >> Starlink mailing list >> [email protected] >> https://lists.bufferbloat.net/listinfo/starlink >> <https://lists.bufferbloat.net/listinfo/starlink> _______________________________________________ Starlink mailing list [email protected] https://lists.bufferbloat.net/listinfo/starlink
